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Spatial correlation of interdecadal variation in global surface temperatures
Geophysical Research Letters
Abstract
We have analyzed spatial correlation patterns of interdecadal global surface temperature variability from an empirical perspective. Using multitaper coherence estimates from 140-yr records, we find that correlations between hemispheres are significant at about 95 percent confidence for nonrandomness for most of the frequency band in the 0.06-0.24 cyc/yr range. Coherence estimates of pairs of 100-yr grid-point temperature data series near 5-yr period reveal teleconnection patterns consistent with known patterns of ENSO variability. Significant correlated variability is observed near 15 year period, with the dominant teleconnection pattern largely confined to the Northern Hemisphere. Peak-to-peak Delta-T is at about 0.5 deg, with simultaneous warming and cooling of discrete patches on the earth's surface. A global average of this pattern would largely cancel.
... As we describe in sections 1 and 3, this ROSI method uses GMSAT as the predictor in the regression calculations. Therefore, we also use a spectral coherence method (e.g., Mann & Park, 1993) to find local regions that have a significant relationship with GMSAT and lead GMSAT variability at interdecadal timescales. ...
... Although the regression-based ROSI method has been previously used to study regions driving GMSAT variability, this method uses GMSAT as the predictor in the regression calculations. Therefore, we compare results derived from the Brown et al. (2015) method with a multitaper spectral coherence approach (Mann & Park, 1993;Thomson, 1982). We use the coherence and phase of local SAT time series and GMSAT in timefrequency space to test where local variability shows a significant lead-lag relationship with global variability in CMIP5 and LMR data. ...
... Traditionally, instrumental, paleoclimate, and climate model data have been used to study internal and externally forced climate variability (e.g., Delworth et al., 1993;Jones, 1989;Manabe & Stouffer, 1996;Mann et al., 1995;Mann & Park, 1994;Stouffer et al., 1994). Instrumental, climate model, and paleoclimate data indicate that physically driven, coupled modes of internal variability may play a role in some degree of regional and global temperature variations (e.g., Kushnir, 1994;Mann & Park, 1993, 1994Mann et al., 1995;Manabe & Stouffer, 1996). However, each of these data sources has its own spatial and temporal limitations, and climate models often disagree on the regions that influence GMSAT (e.g., Brown et al., 2015). ...
Despite the importance of interdecadal climate variability, we have a limited understanding of which geographic regions are associated with global temperature variability at these timescales. The instrumental record tends to be too short to develop sample statistics to study interdecadal climate variability, and Coupled Model Intercomparison Project, Phase 5 (CMIP5) climate models tend to disagree about which locations most strongly influence global mean interdecadal temperature variability. Here we use a new paleoclimate data assimilation product, the Last Millennium Reanalysis (LMR), to examine where local variability is associated with global mean temperature variability at interdecadal timescales. The LMR framework uses an ensemble Kalman filter data assimilation approach to combine the latest paleoclimate data and state‐of‐the‐art model data to generate annually resolved field reconstructions of surface temperature, which allow us to explore the timing and dynamics of preinstrumental climate variability in new ways. The LMR consistently shows that the middle‐ to high‐latitude north Pacific and the high‐latitude North Atlantic tend to lead global temperature variability on interdecadal timescales. These findings have important implications for understanding the dynamics of low‐frequency climate variability in the preindustrial era.
... We investigate the geographic regions associated with GMST variability (e.g., Brown et al., 2016;Manabe & Stouffer, 1996;Mann & Park, 1993;Stouffer et al., 2000) using a multitaper spectral coherence approach (Mann & Park, 1993;Parsons & Hakim, 2019;Thomson, 1982) in CMIP3, CMIP5, and CMIP6 piControl simulations and CMIP6 historical simulations (1915-2014 CE; Table S1), and gridded instrumental-based surface temperature data (GISTEMP, BE, 20CRv3 1915. In the instrumental-based data and the CMIP6 historical simulations, we do not remove the linear trends from local TS prior to conducting coherence calculations in order to examine the differences in the patterns of coherence between forced and unforced variability. ...
... We investigate the geographic regions associated with GMST variability (e.g., Brown et al., 2016;Manabe & Stouffer, 1996;Mann & Park, 1993;Stouffer et al., 2000) using a multitaper spectral coherence approach (Mann & Park, 1993;Parsons & Hakim, 2019;Thomson, 1982) in CMIP3, CMIP5, and CMIP6 piControl simulations and CMIP6 historical simulations (1915-2014 CE; Table S1), and gridded instrumental-based surface temperature data (GISTEMP, BE, 20CRv3 1915. In the instrumental-based data and the CMIP6 historical simulations, we do not remove the linear trends from local TS prior to conducting coherence calculations in order to examine the differences in the patterns of coherence between forced and unforced variability. ...
Plain Language Summary
Ongoing and future global and regional warming will progress as a combination of internal climate variability and forced climate change. Understanding the magnitude and spatial patterns associated with internal climate variability is an important aspect of being able to predict when, where, and how climate change will be felt around the globe. Here, we show that the latest climate model simulations, which will be used in the Intergovernmental Panel on Climate Change (IPCC) Assessment Report 6 (AR6), simulate a large range in magnitudes of internal global mean temperature variability. Although there are large unforced global temperature trends in some models, we find that even the most variable models never generate unforced global temperature trends equal to the recently observed global warming trends forced by greenhouse gas emissions. We examine the regions associated with internal climate variability and forced climate change in climate model simulations and find that only forced simulations show a pattern of warming consistent with instrumental data.
... The case p ϭ 1 and K ϭ 1 is simply the single-tapered discrete Fourier transform (DFT) of Blackman and Tukey [1958]. For instrumental climate records, with a typical length of a few hundred points, the choice p ϭ 2 and K ϭ 3 offers a good compromise between the required frequency resolution for resolving distinct climate signals (e.g., ENSO and decadal-scale variability) and the benefit of multiple spectral degrees of freedom, i.e., of reduced variance [e.g., Mann and Park, 1993]. Longer data sets permit the use of a greater number K of tapers while maintaining a desired frequency resolution. ...
... [133] Because of the improvements in its spectral estimation properties over the classical methods of section 3.2, the MTM method has been widely applied to problems in geophysical signal analysis, including analyses of instrumental data on the atmosphere and oceans [Kuo et al., 1990;Ghil and Vautard, 1991;Mann and Park, 1993, 1996a, 1996bLall and Mann, 1995;Mann et al., 1995b;Thomson, 1995], paleoclimate proxy data [Chappellaz et al., 1990;Thomson, 1990aThomson, , 1990bBerger et al., 1991;Mann et al., 1995a;Mann and Lees, 1996;Mommersteeg et al., 1995;Park and Maasch, 1993;Yiou et al., 1991Yiou et al., , 1994Yiou et al., , 1995Yiou et al., , 1997, geochemical tracer data [Koch and Mann, 1996], and seismological data [Park et al., 1987;Lees, 1995]. Time-frequency "evolutive" analyses based on moving-window adaptations of MTM have also been applied to paleoclimatic records and model simulations [Yiou et al., 1991;Birchfield and Ghil, 1993;Mann et al., 1995a;Mann and Park, 1996b]. ...
... In the absence of other information, the e-folding length scale (that is, the separation at which the correlation falls to e −1 ) of annual mean surface temperature anomalies was used as a rough guide in specifying these priors. Figure 3 of Hansen and Lebedeff [1987] suggests an e-folding length scale of about 1750km in the mid-to high-latitudes, while Mann and Park [1993] and Tingley and Huybers [2010] estimate length scales of 1500km and 1800km, respectively, using global data. Informed by these studies, identical Gamma priors are chosen for φ α and φ β , with means of 1000km and, to allow for a fair amount of uncertainty, 5th and 95th ...
... Fig. 4(a) shows the prior density for φ β (equivalently for φ α ). A prior mean is chosen smaller than the values suggested in Hansen and Lebedeff [1987], Mann and Park [1993] and Tingley and Huybers [2010] as our aim is to model spatial structure in the limited spatial domain considered here. In addition, there is no simple way to link the characteristic length scale of instrumental temperature anomalies to that for the distributional parameters governing extremal behavior in climate-sensitive tree ring series, so the studies of the instrumental record are used as no more than a rough guide. ...
... reduce variance compared to the classical non-parametric Fourier analysis. We chose a tape bandwidth 140 parameter of 2 and 3 tapers since this selection has been shown to be a good compromise between the 141 required frequency resolution and the spectral variance for daily timeseries (e.g., Mann and Park, 1993). ...
Persistent fluctuations in the latitudinal position of the North Atlantic (NATL) jet stream are associated with extreme weather anomalies, particularly over Europe. Therefore, it is crucial to understand how the jet stream persistence might change in response to increased greenhouse gases to deliver useful regional climate projections. This study examines the persistence of the North Atlantic jet stream latitudinal fluctuations in CMIP6 and ERA5. We found that CMIP6 models consistently overestimate the persistence compared to ERA5 during the historical period. This discrepancy appears linked to too weak transient eddies over the NATL in CMIP6 models.
By the end of the XXI century, CMIP6 models forced with the SSP585 scenario project a reduction of the jet fluctuations persistence of about 10% during the summer season. The evidence suggests this reduction is linked to a slower NATL jet during the summer months.
... The higher surface temperatures over the central Pacific, called as El Niño-Modoki (Ashok et al. 2007), also cause deficit monsoon rainfall over India while following a different spatial pattern (Sahastrabuddhe et al. 2019). ENSO and Indian monsoon also have decadal and multidecadal teleconnection variability (Mann & Park 1993Gershunov & Barnett 1998). ...
Indian Summer Monsoon Rainfall (ISMR) is one of the most well-documented areas of hydrometeorology; however, the processes associated with ISMR are not well understood. This attributes to the complexities associated with ISMR at multiple spatio-temporal scales. This further results in inconsistencies across the literature to assess the impacts of global warming on the monsoon, though this has huge relevance as a huge population of South Asia is dependent on the same. Here, we review and assess the existing literature on the Indian monsoon, its variability, and its trajectory in a warming scenario. We further synthesize the literature on its impacts on the hydrology of major river basins in South Asia. We also identify a few research questions, addressing which will add value to the understanding of the Indian monsoon and the associated water cycle. We have highlighted that there is a significant lack of understanding of how different large-scale and regional factors affect ISMR at different timescales. These impacts, in turn, get translated into hydrology and water sector in India. There is a need to know where we stand to combat the impacts of climate change on ISMR, which can be translated to adaptation by policy-making processes and water management practices in India.
HIGHLIGHTS
The study reviews the literature regarding the Indian monsoon in changing climate over time.;
Studies regarding the changing characteristics and the factors affecting the Indian monsoon have been reviewed.;
Few research questions are discussed that can be addressed to improve the understanding of the Indian monsoon.;
Study can be a guideline for future research regarding the simulation and prediction/projection of the Indian monsoon.;
... No entanto, como a extensão de registros tem aumentado, os hidrólogos tomaram consciência da estrutura de baixa frequência do clima -por exemplo, oscilações ENSO, PDO, NAO -e têm procurado desenvolver cenários de vazões considerando essa variabilidade (Dettinger et al, 1995;. Ghil e Vautard, 1991;Keppenne e Ghil, 1992a;Keppenne e Lall, 1996;Lall e Mann, 1995;Mann e Park, 1993Know et al., 2007;Souza Filho et al., 2008). ...
Barroso, G. F. (2014). Lagunas, lagoas e lagos costeiros. In: Assad, E. D. & Magalhães, A. (eds.). Impactos, vulnerabilidades e adaptação às mudanças climáticas. Contribuição do Grupo de Trabalho 2 do Painel Brasileiro de Mudanças Climáticas ao Primeiro Relatório da Avaliação Nacional sobre Mudanças Climáticas. Rio de Janeiro, PBMC/COPPE, Universidade Federal do Rio de Janeiro. 2: 89-99p.
... No entanto, como a extensão de registros tem aumentado, os hidrólogos tomaram consciência da estrutura de baixa frequência do clima -por exemplo, oscilações ENSO, PDO, NAO -e têm procurado desenvolver cenários de vazões considerando essa variabilidade (Dettinger et al, 1995;. Ghil e Vautard, 1991;Keppenne e Ghil, 1992a;Keppenne e Lall, 1996;Lall e Mann, 1995;Mann e Park, 1993Know et al., 2007;Souza Filho et al., 2008 A irrigação é responsável pela maior parte da água captada, com a vazão de retirada no País estimada em 866 m 3 /s -ou 47% do total -e também, pela maior participação no consumo de água, correspondendo a 69% (PNRH, 2006a). ...
... To estimate the coherence of two individual time series, we apply two different methods. First, we derive the coherence across two time series by following closely Vernon et al. (1991), Mann and Park (1993), and Lall and Mann (1995): The coherence of two signals is determined by the individual spectral density functions of the series using the MTM. We refer to this as MTM coherence. ...
Mercury is characterized by a very peculiar magnetic field, as it was revealed by the MESSENGER mission. Its internal component is highly axisymmetric, dominated by the dipole, and very weak. This in turns leads to a very dynamic magnetosphere. It is known that there exist relationships between the internally generated field and the external field, although their dynamics are complex. In this study we derive steady and time‐varying spherical harmonic models of Mercury's magnetic field using MESSENGER measurements and interpret these models both in terms of correlated features and of the internal structure of Mercury. The influence of the hemispheric data distribution of MESSENGER is evaluated to grant the robustness of our models. We find a quadrupole‐to‐dipole ratio of 0.27 for the steady magnetic field. The time‐varying models reveal periodic and highly correlated temporal variations of internal and external origins. This argues for externally inducing and internally induced sources. The main period is 88 days, the orbital period of Mercury around the Sun. There is no measurable time lag between variations of external and internal magnetic fields, which place an upper limit of 1 S/m for the mantle conductivity. Finally, the compared amplitudes of external and internal time‐varying field lead to an independent (from gravity studies) estimate of the conductive core radius, at 2,060 ± 22 km. These analyses will be further completed with the upcoming BepiColombo mission and its magnetic field experiment, but the presented results already lift the veil on some of the magnetic oddities at Mercury.
... Previous studies to quantify the influence of climate change on coastal upwelling [1] used climate models with much simpler representations of the ocean than are common today. A number of recent papers have explored the patterns and dynamics of fluctuations embedded within the long-term, globally integrated tendency commonly referred to as climate change [2][3][4][5][6]. However, these studies have concentrated on large-scale temporal oscillations, generally on decadal scales; fewer examples describe variability on subbasin (i.e., 100-1000km) space scales. ...
... The MTM spectral analysis was implemented using the MTM-SSA Toolkit with robust background estimation (Ghil et al., 2002). Following the suggestion of Mann and Park (1993), where climate records consist of a few hundred observations, three tapers and a bandwidth parameter p = 2 were employed. As a complement to the MTM method, a wavelet analysis was used to highlight the evolution of significant frequencies of variability in the April 1 SWE reconstruction over time (Grinsted, Moore, & Jevrejeva, 2004;Torrence & Compo, 1998). ...
Long hydroclimate records are essential elements for the assessment and management of changing freshwater resources. These records are especially important in transboundary watersheds where international cooperation is required in the joint planning and management process of shared basins. Dendrochronological techniques were used to develop a multi‐century record of April 1 snow water equivalent (SWE) for the Stikine River watershed in northwestern British Columbia, Canada, from moisture‐sensitive white spruce (Picea glauca) tree rings. Explaining 43% of the instrumental SWE variability, to our knowledge this research represents the first attempt to develop long‐term snowpack reconstructions in northern British Columbia. The results indicated that 15 extreme low April 1 SWE events occurred from 1789 to the beginning of the instrumental record in 1974. The reconstruction record also shows that the occurrence of hydrologic extremes in the Stikine basin is characterized by persistent below‐average periods in SWE consistent with phase shifts of the Pacific Decadal Oscillation (PDO). Spectral analyses indicate a very distinct in‐phase (positive) relationship between the multidecadal frequencies of variability (~40 years) extracted from the SWE tree‐ring reconstruction and other reconstructed winter and spring PDO indices. Comparison of the reconstructed SWE record with other tree ring‐derived PDO proxy records show coherence at multidecadal frequencies of variability. The research has significant implications for regional watershed management by highlighting the hydrological response of the Stikine River basin to prior climate changes.
... Over the past few decades many authors and teams studied the low-frequency variability in climate variables in order to assess and possibly separate the anthropogenic climate change from the natural variability on long temporal scales (see e.g. Ghil and Vautard [1991]; Mann and Park [1993]; Allen and Smith [1994]; Plaut and Vautard [1994]; Dettinger et al. [1995]; Folland et al. [2002]; Viron et al. [2013] and many more). This is crucial for our understanding of the climatic response to increasing greenhouse-gas and aerosol concentration, and ultimately for the prediction of future climate on Earth. ...
Earth climate, in general, varies on many temporal and spatial scales. In particular, climate observables exhibit recurring patterns and quasi-oscillatory phenomena with different periods. Although these oscillations might be weak in amplitude, they might have a non-negligible influence on variability on shorter time-scales due to cross-scale interactions, recently observed by Paluš [2014]. This thesis supplies an introductory material for inferring the cross-scale information transfer from observational data, where the time series of interest are obtained using wavelet transform, and possible information transfer is studied using the tools from information theory. Finally, cross-scale interactions are studied in two climate phenomena: air temperature variability in Europe, in which we study phase-amplitude coupling from a slower oscillatory mode with an 8-year period on faster variability and its effects, and El Niño/Southern Oscillation where we observe a causal chain of phase-phase and phase-amplitude couplings among distinct oscillatory modes.
... No entanto, como a extensão de registros tem aumentado, os hidrólogos tomaram consciência da estrutura de baixa frequência do clima -por exemplo, oscilações ENSO, PDO, NAO -e têm procurado desenvolver cenários de vazões considerando essa variabilidade (Dettinger et al, 1995;. Ghil e Vautard, 1991;Keppenne e Ghil, 1992a;Keppenne e Lall, 1996;Lall e Mann, 1995;Mann e Park, 1993Know et al., 2007;Souza Filho et al., 2008). ...
A mudança climática é um dos desafios mais complexos deste século. Nenhum país está imune a ela
nem pode vir a ser capaz de enfrentar individualmente os desafios interconectados que compreendem
decisões políticas e econômicas controversas. Tampouco, os avanços tecnológicos com consequências
globais de longo alcance (Banco Mundial, 2010a).
Estudos científicos, publicados em 2007 no Quarto Relatório de Avaliação (AR4) do Painel Intergovernamental sobre Mudanças Climáticas (IPCC), indicaram que as alterações do clima relativas ao aquecimento global e ao aumento do nível do mar podem estar se intensificando. Estas alterações já
estão ocorrendo e podem ser verificadas através dos registros sobre eventos extremos, cada vez mais
frequentes.
As alterações climáticas provocam mudanças nos sistemas geofisicos, biólogicos e humanos. Dessa
maneira, impõem uma série de desafios ao desenvolvimento, com implicações sobre diversos setores:
sociais, econômicos e ambientais, relacionados à indústria, agricultura, comércio, segurança e bem-estar social (IPCC, 2007).
Segundo O’Brien e Leichenko (2008), as avaliações realizadas pelo IPCC confirmam que a mudança climática está contribuindo para transformações significativas do ambiente biofísico que afetarão ecossistemas, assentamentos humanos e recursos hídricos, bem como a produção de alimentos. Essas transformações poderão ter grandes implicações para nações, regiões, comunidades e indivíduos. À medida que a temperatura do ar da Terra aumenta os padrões pluviais mudam e eventos climáticos extremos, como secas, inundações e incêndios florestais, se tornam mais frequentes. Milhões de pessoas em áreas costeiras enfrentarão problemas relativos a enchentes e inundações associadas a tempestades e ao aumento do nível do mar (Banco Mundial, 2010a). Embora haja uma considerável incerteza sobre a trajetória futura da mudança climática, relacionada em parte com a quantidade e a taxa de emissões de gases de efeito estufa (GEEs), as consequências das mudanças representam uma ameaça sem precedentes à segurança humana (O’Brien e Leichenko, 2008). Na décima sexta Conferência das Partes (COP16), realizada em Cancun, no México, em 2010, destacou-se como principais compromissos assumidos pelas nações participantes, a redução de 1,5 ºC na temperatura do ar em futuro próximo; a adoção de mecanismos de desenvolvimento limpo (MDL)
e a difusão de novas tecnologias menos emissoaras de GEE; a criação do Fundo Climático Verde para
se financiar projetos, programas, políticas e outras atividades nos países em desenvolvimento, e, a
criação de um comitê de adaptação para promover a implantação de medidas mais coesas.
Em 2011, no encontro da Organização das Nações Unidas sobre Mudança do Clima, realizado em
Durban, na África do Sul, foi entregue um documento reforçando a necessidade de implementação
do Protocolo de Quioto, do Plano de Ação definido na Indonésia em 2007, durante a COP13 e dos
acordos alcançados em Cancun, na tentativa de se evitar um retrocesso das negociações.
Visando compreender a realidade nacional, especialistas brasileiros se reuniram em 2011 para a
elaboração do Primeiro Relatório de Avaliação Nacional (RAN1) do Painel Brasileiro de Mudanças
Climáticas (PBMC). Tal documento se refere aos trabalhos realizados pelo Grupo de Trabalho 2 (GT-2)
sobre Impactos, Mitigação e Adaptação às Mudanças Climáticas, com o objetivo de fornecer subsídios
para decisões relativas às medidas de mitigação e à adaptação as mudanças climáticas no País.
A avaliação teve como ponto de partida os trabalhos científicos mais recentes, retratando de forma
ampla e atualizada os impactos causados pelas mudanças do clima no Brasil; a vulnerabilidade dos
ambientes naturais e humanos, e ainda, as medidas necessárias para se adaptar a esses efeitos e a
mitigá-los.
A questão central seria: como tornar o País mais resiliente à mudança do clima sem o aumento contínuo das emissões de GEEs e da degradação dos ecossistemas e, ao mesmo tempo, seguir perseguindo seu crescimento econômico? A mudança climática torna o desafio do desenvolvimento mais complicado, pois seu impacto pode ser sentido no aumento da frequência de ocorrência de tempestades, inundações, ondas de calor, secas e elevação do nível do mar, sobrecarregando todos os setores da sociedade brasileira.
As nações, de um modo geral, e substancialmente, os países em desenvolvimento precisam de expansões expressivas em sistemas de energia, transporte, produção agrícola e avanços tecnológicos.
Entretanto, se os meios tradicionais forem mantidos, as extensões, tão necessárias, produzirão mais
aquecimento em virtude das emissões de GEEs que provocarão (Banco Mundial, 2010a).
Um aquecimento adicional relativamente modesto exigirá grandes ajustes na forma como as políticas
de desenvolvimento são planejadas e implementadas, bem como na maneira como as pessoas vivem
e se sustentam. A questão não é simples, tampouco uma relação direta entre crescimento e emissões
de carbono para atmosfera, pois muitos processos produtivos ineficientes, usos irracionais dos recursos
naturais e desperdícios são responsáveis pelo aumento da concentração de CO2 na atmosfera (Banco
Mundial, 2010a).
A situação atual do clima exige grandes mudanças no estilo de vida, uma verdadeira revolução energética e a transformação do modo como lidamos com os recursos naturais. Nesse sentido, um processo de adaptação substancial é fundamental para se tentar reverter o panorama atual.
Dentro desse contexto, um panorama inicial das mudanças climáticas e a conjuntura nacional são
analisados no capítulo 3 do volume II do Relatório de Avaliação Nacional I do Painel Brasileiro de
Mudanças Climáticas. Já as principais questões avaliadas são discutidas no capítulo 4, dedicado ao tema dos recursos naturais e aos usos de manejos dos ecossistemas. Seu principal enfoque recai sobre os recursos hídricos, envolvendo os ecossistemas de água doce e terrestre, os sistemas costeiros e a segurança alimentar. Por sua vez, ao capítulo 5, a discussão trata dos aglomerados urbanos, da indústria e de infraestrutura. Neste último caso, a maior dificuldade foi encontrar literatura científica a respeito.
Ficou evidente a necessidade de se buscar mais informações sobre as questões de vulnerabilidade e de
adaptação relativas a este importante setor da sociedade brasileira.
No capítulo 6, as questões da saúde humana, do bem estar e de segurança são abordadas. Vários
trabalhos foram realizados nos últimos cinco anos sobre o primeiro desses temas. Porém, há claro desequilíbrio regional sobre as informações referentes aos impactos causados pelas mudanças climáticas
sobre ele.
Destaque especial foi dado aos temas subsistência e pobreza. Primeiro, por conta da dificuldade de se encontrar no País, referências científicas sobre a relação entre mudança climática e o assunto em questão. Segundo, porque é claro e evidente que as populações mais pobres serão as mais atingidas pelas alterações de clima. Daí a necessidade, de se apoiar, em futuro próximo, trabalhos que busquem fortalecer a pesquisa científica com forte aderência de questões relativas a recursos naturais à socioeconômica.
Ao capítulo 7 deste volume, são discutidas as questões relativas à adaptação e ao desenvolvimento econômico seus riscos, vulnerabilidades e oportunidades. Uma abordagem econômica é feita nesse
sentido, buscando coligir o que foi feito no País durante os últimos anos.
Finalmente, ao capítulo 8, os impactos intersetorias, vulnerabilidades e oportunidades são discutidos em cinco diferentes seções, que buscam regionalizar as abordagens.
As estruturas desses capítulos diferem entre si. Isso se explica pela quantidade de literatura científica, farta em algumas regiões do País – Sudeste, Sul, e norte por exemplo – e menor, nas regiões Nordeste e Centro-Oeste.
Com base na análise de documentos e em discussões realizadas entre os especialistas, considera-se que os impactos físicos, biológicos e humanos associados às mudanças do clima deverão variar consideravelmente no território brasileiro de acordo com características regionais, níveis de exposição e graus de degradação ambiental.
Todas as esferas de governo, a indústria, o comércio e a sociedade precisam estar envolvidos no
desenvolvimento de uma resposta nacional adequada. Portanto, o entendimento dessas alterações
climáticas em cada região é essencial para um planejamento estratégico e o processo de tomada de
decisão. Foi essa a base da abordagem do trabalho do GT2.
... In this paper, the SSA-MTM toolkit is applied to identify dominant oscillation modes in spring discharge, climate indices, and meteorological parameters, and to reconstruct significant quasi-periodic signals (Dettinger et al. 1995;Ghil et al. 2002). A nearly optimal reconstruction can always be obtained through seeking the weighted linear combination of three lowest-order boundary constraints that minimize the mean-square misfit of the reconstructed signal with respect to the raw data series (Mann and Park 1993). ...
The Niangziguan Springs (NS) discharge is used as a proxy indicator of the variability of the karst groundwater system in relation to major climate indices such as El Niño-Southern Oscillation (ENSO), Pacific decadal oscillation (PDO), Indian summer monsoon (ISM), and west North Pacific monsoon (WNPM). The relationships between spring discharge and these climate indices are determined using the multitaper method (MTM), continuous wavelet transform (CWT), and wavelet transform coherence (WTC). Significant periodic components of spring discharge in the 1-, 3.4-, and 26.8-yr periodicities are identified and reconstructed for further investigation of the correlation between spring discharge and largescale climate patterns on these time scales. Correlation coefficients andWTC between spring discharge and the climate indices indicate that variability in spring discharge is significantly and positively correlated with monsoon indices in the 1-yr periodicity and negatively correlated with ENSO in the 3.4-yr periodicity and PDO in the 26.8-yr periodicity. This suggests that the oscillations of the spring discharge on annual, interannual, and interdecadal time scales are dominated by monsoon, ENSO, and PDO in the NS basin, respectively. Results show that monsoons modulate the spring discharge by affecting local meteorological parameters. ENSO and PDO impact the variability of the NS discharge by affecting the climate conditions in northern China.
... r 2 <0.25) at station distance of about 1.200 km on average, being this distance lower at low latitudes than at high latitudes, "probably as a consequence of the dominance of mixing by large-scales eddies at high latitudes". Different results were reported by Jones et al. (1997) who found higher values of CDD in tropical areas than in mean latitudes; they suggest a global mean value around 1500 km at which r<0.5, similar to those reported by Mann and Park (1993), Madden et al. (1993), Caesar et al. (2006), Kim and North (1991) and Osborn and Hulme (1997). A global mean value of 1200 km was used by Mitchell and Jones (2005), following the study of New et al. (2000), for global database preparation. ...
The spatial variability of monthly diurnal and nocturnal mean values of temperature in Spain has been analysed to evaluate the optimal threshold distance between neighbouring stations that make a meteorological network (in terms of stations’ density) well representative of the conterminous land of Spain. To this end, the correlation decay distance has been calculated using the highest quality monthly available temperature series (1981–2010) from AEMet (National Spanish Meteorological Agency). In the contermi- nous land of Spain, the distance at which couples of stations have a common variance above the selected threshold (50 %, r Pearson ∼0.70) for bothmaximum and minimumtemperature on average does not exceed 400 km, with relevant spatial and temporal differences, and in extended areas of Spain, this value is lower than 200 km. The spatial variability for mini- mum temperature is higher than for maximum, except in cold months when the reverse is true. Spatially, highest values are located in both diurnal and nocturnal temperatures to the southeastern coastland and lower spatial variability is found to the inland areas, and thus the spatial variability shows a clear coastland-to-inland gradient at annual and monthly scale.Monthly analyses show that the highest spatial variabil- ity in maximumand minimumtemperatures occur in July and August, when radiation is maximum, and in lowland areas, (<200 m o.s.l.), which coincide with the mostly transformed landscapes, particularly by irrigation and urbanization. These results highlight local factors could play a major role on spatial variability of temperature. Being maximum and minimum temperature interstation correlation values highly variable in Spanish land, an average of threshold distance of about 200 km as a limit value for a well representative network should be recommended for climate analyses.
... In the context of linear prediction and extracting sinusoids in noise it is known as the Cadzow iteration [34][35][36]. In the context of chaotic dynamics, climatology, and meteorology, it is known as singular spectral analysis (SSA) † [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103]; ...
... Coherence analysis of the seismometer channels is useful to infer the different background noise sources and to identify coherent signals that can be subtracted from the vertical channel to reduce noise levels [Crawford and Webb, 2000]. We apply the code by Park adapted by Mann [Mann and Park, 1993, and references therein] which calculates complex multitaper (MTM) spectral coherence of two data series. Coherence analysis was applied to 2 segments of data, using 6 4p-prolate Slepian tapers. ...
[1] We show over 4 months of 3-component broadband seismometer data from the SN-1 seafloor multidisciplinary observatory, deployed offshore of Eastern Sicily (Italy) at 2105 m b.s.l. The SN-1 spectra show background noise levels above 0.1 Hz similar to levels at a nearby ground station. An important noise source below 0.1 Hz is caused by tilt of the sensor induced by sea currents. Seismic noise levels above 0.01 Hz are strongly dependent on Etna volcanic activity. In spite of these intense noise sources, SN-1 recorded many local, regional and global events. The quality of seismic recordings confirms the validity of the installation procedure and good ground coupling of the 3-component broadband sensor, suggesting that SN-1 can be proposed as permanent observatory in this high seismic and volcanic hazard area.
... Although year-to-year climate variations may look random, careful investigation of historical data can sometimes expose clear patterns of atmospheric and oceanic anomalies that recur every few years in almost similar forms and sequences (Mann and Park, 1993;Mann and Park, 1994); e.g. due to association with variations in teleconnection indices. ...
Annual, seasonal and monthly variations in precipitation during the period 1911–2011 were evaluated using spatially interpolated monthly precipitation records at 165 stations with more than 30 years of data (of which 32 stations had 101 years of data referring to full length of study period). Historical trends and cyclic patterns of precipitation and links to teleconnection indices were analysed. The results show that annual precipitation in Finland increased by 0.92 ± 0.50 mm year−1 (p < 0.05) during the study period (1911–2011), and showed negative relationships with the East Atlantic/West Russia (EA/WR) teleconnection pattern (ρ = −0.41, p < 0.05) through the years 1950–2011. However, there were spatial (north–south/east–west) differences between regions. The time cycle (λ) for annual precipitation cycles was estimated to 149 years (R2=0.15), and 1964 was indicated as the turning point from a negative (dry) to a positive (wet) phase. Analysis of seasonal and monthly cycles showed larger variations, depending mainly on teleconnection effects. Analysis of seasonal precipitation determined increasing trends for winter (by 0.46 ± 0.19 mm year−1) and summer (by 0.32 ± 0.29 mm year−1), while no clear trend was found for spring and autumn precipitation (p > 0.05). Winter precipitation was most strongly correlated with the North Atlantic Oscillation (NAO) index (ρ = 0.55, p < 0.05), while the EA/WR pattern was the most significant teleconnection index for precipitation variations in spring (ρ = −0.33, p < 0.05) and summer (ρ = −0.49, p < 0.05); the precipitation variability during autumn was negatively associated with the Scandinavia (SCA) pattern (ρ = −0.40, p < 0.05). The results clearly indicate that Finland has experienced wetter climate than normal conditions during recent decades, and precipitation in the Fenno-Scandinavian climate is controlled by a number of climate teleconnection indices, not just the NAO as previously assumed.
... All RPI records represented in Fig. 7 were interpolated to equal (1-kyr) spacing in order to apply methods of spectral analysis, including the MultiTaper method (MTM) (Thomson, 1982;Percival and Walden, 1993;Mann and Park, 1993). Power and coherence spectra are compared with the background red noise estimates at the 99% significance level (Mann and Lees, 1996). ...
Late Oligocene to Early Miocene relative paleointensity (RPI) proxies can be correlated from the equatorial Pacific (IODP Site U1334 and ODP Site 1218) to the South Atlantic (ODP Site 1090). Age models are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale. The RPI records do not contain significant power at specific (orbital) frequencies, and hence there is no significant coherency between RPI proxies and the normalizers used to construct the proxies, although orbital power is present in some normalizers. There is no obvious control on RPI proxies from mean sedimentation rate within polarity chrons, magnetic grain size proxies or magnetic concentration parameters. The salient test is whether the equatorial Pacific records can be correlated one to another, and to the records from the South Atlantic. All records are dominated by RPI minima at polarity reversals, as expected, although the comparison within polarity chrons is compelling enough to conclude that the intensity of the Earthʼs axial dipole is being recorded. This is supported by the fit of RPI data from Sites U1334 and 1218 after correlation of the two sites using diverse core-scanning data, rather than polarity reversals alone. We do not see a consistent relationship between polarity-chron duration and mean RPI, and no consistent skewness (“saw-tooth” pattern) for RPI within polarity chrons. Stacks of RPI records for 17.5–26.5 Ma include long-term changes in RPI on Myr timescales that are superimposed on RPI minima associated with polarity reversals, and shorter-term variations in RPI with an apparent pacing of ∼50 kyr∼50 kyr. The equatorial Pacific to South Atlantic correlations indicate that RPI can be used as a (global) stratigraphic tool in pre-Quaternary sediments with typical pelagic sedimentation rates of a few cm/kyr.
... We applied the SSA-MTM toolkit [Ghil et al., 2002], with robust background estimation, to the residual time series. The bandwidth parameter p was set at two and the numbers of tapers was set at three, which has been suggested for the analysis of climate records consisting of a few hundred observations [Mann and Park, 1993]. ...
Thirty one hydrological time series of shallow groundwater levels,
precipitation, and moisture-sensitive tree ring chronologies were
analyzed and related to two climate indices: Niño 3.4 and PDO.
Spearman rank correlation and spectral analyses (multitaper method,
continuous wavelet transform, and wavelet coherence) were used to
document the influence of El Niño Southern Oscillation (ENSO) and
the Pacific Decadal Oscillation (PDO) on shallow (depth < 20 m)
groundwater level records from the Canadian Prairies. Modes of
variability in the 2-7, 7-10, and 18-22 year bands were detected and
reconstructed. Correlations and wavelet coherence between these
oscillation modes and the climate indices suggest that variability in
the 2-7 and 7-10 year bands is highly influenced by ENSO. The
oscillation modes in the 18-22 year band reflect a negative correlation
with the PDO index. When either of these teleconnections (ENSO/PDO) is
in their respective positive phases, groundwater levels reflect the
effect of associated warmer and drier winters experienced over much of
interior Canada and the US, affecting important resource inputs to the
hydrological cycle and groundwater recharge.
... ), has a similar purpose as the MTM singular value decomposition (e.g., Mann and Park 1993), but is different in that we were interested in the identification of a spectral bandwidth, rather than specific spectral peak(s) of variability. Figure 3a shows that the coherence amplitudes at or above the 90% confidence interval appear in the Great Basin with simultaneous phases (08) and in the eastern Rocky Mountains and the southwest with shifted phases (458–908). ...
This study investigates the meteorological conditions associated with multidecadal drought cycles as revealed by lake level fluctuation of the Great Salt Lake (GSL). The analysis combined instrumental, proxy, and simulation datasets, including the Twentieth Century Reanalysis version 2, the North American Drought Atlas, and a 2000-yr control simulation of the GFDL Coupled Model, version 2.1 (CM2.1). Statistical evidence from the spectral coherence analysis points to a phase shift amounting to 6-9 yr between the wet dry cycles in the Great Basin and the warm cool phases of the interdecadal Pacific oscillation (IP0). Diagnoses of the sea surface temperature and atmospheric circulation anomalies attribute such a phase shift to a distinctive teleconnection wave train that develops during the transition points between the IPO's warm and cool phases. This teleconnection wave train forms recurrent circulation anomalies centered over the southeastern Gulf of Alaska; this directs moisture flux across the Great Basin and subsequently drives wet dry conditions over the Great Basin and the GSL watershed. The IPO life cycle therefore modulates local droughts pluvials in a quarter-phase manner.
... We calculated the synthetic seismograms corresponding to the transverse component of ground motion, since they depend only on Qs, and we compare them to those calculated for the model in Table 1. The comparison is carried out in terms of the squared coherency calculated between the seismograms estimated using the complex multitaper spectral coherence as proposed in Mann & Park (1993), and Mann et al. (1995). Multitaper methods offer the opportunity to compute the coherence by applying some kind of time-frequency ensemble, using the FFT of the considered seismograms tapered with a certain taper. ...
The estimation of shear wave velocity and attenuation in near-surface
geology is of primary importance in engineering seismology. In fact,
their knowledge is essential for site response studies when preparing
improved seismic hazard scenarios. In this study, we propose two
approaches for estimating the average shear wave quality factor Qs by
using recordings of a vertical array of accelerometers. The methods are
mainly based on the deconvolution of the wavefield recorded in a
borehole with that recorded at the surface.
The first method requires the Fourier transform of the deconvolved
wavefield to be fitted with a theoretical transfer function valid for
the vertical or nearly vertical (in the case at hand up to 30°
incidence angle) propagation of S waves. The second method is based on
the spectral fitting of the Fourier transform of only the acausal part
of the deconvolved wavefield with a theoretical transfer function.
Both methods can be applied without any prior knowledge of the subsoil
structure (since they are based on empirical data analysis) and do not
require a precise knowledge of the azimuthal orientation of the sensors
in the boreholes (which is seldom available). First, we describe the
theoretical framework of the proposed methodologies for Qs estimation,
which are based on the assumption that the structure in the borehole is
weakly heterogeneous in the vertical direction (i.e. no large impedance
contrast exists between the borehole sensor and the surface). Second, by
using synthetic accelerograms, we verify that in a realistic subsoil
structure, the assumption of vertical homogeneity can hold and we
investigate the robustness and the suitability of the proposed methods.
Finally, only the method that was shown to provide the more stable
results, based on fitting the borehole-to-surface spectral ratio with a
theoretical function, is applied to earthquakes signals recorded by a
vertical array of accelerometers installed in Ataköy (western
Istanbul). Results show that using borehole data provides a fair and
robust estimate of an average Qs (of about 30, 46 and 99 for the 0-50,
0-70, 0-140 m depth ranges, respectively) that can be used for numerical
simulations of ground motion.
... 4–5- yr variability have been documented in the South Atlantic by Mehta and Delworth (1995) , in rainfall in of the spectrum is shown). For MTM analysis the resolution has been set to 2 and the number of tapers to 3, which is thought to be the best compromise for climate signals (Mann and Park 1993). For SSA analysis a wide range of window lengths were tested and the results for a window length M 168 months are shown; windows shorter than 100 months did not clearly separate the QB and 5-yr scales, although Vautard et al. (1992) suggest that SSA is typically successful in analyzing periods in the range [M/5, M]. zil by Mehta (1998), in tropical Atlantic SST by Tourre et al. (1999), and associated with ENSO forcings via extratropical Pacific South American (PSA) patterns by Mo (2000). ...
When sea surface temperatures are prescribed at its lower boundary, the University of California, Los Angeles (UCLA) atmospheric general circulation model (AGCM) produces a realistic simulation of planetary boundary layer (PBL) stratocumulus cloud incidence. Despite this success, net surface solar fluxes are generally overpredicted in comparison to Earth Radiation Budget Experiment (ERBE) derived data in regions characterized by persistent stratocumulus cloud decks. It is suggested that this deficiency is due to the highly simplified formulation of the PBL cloud optical properties. A new formulation of PBL cloud optical properties is developed based on an estimate of the stratocumulus cloud liquid water path. The January and July mean net surface solar fluxes simulated by the revised AGCM are closer to ERBE-derived values in regions where stratocumulus clouds are frequently observed. The area-averaged estimated error reductions range from 24 (Peru region) to 53 W m-2 (South Pacific storm track region). The results emphasize that surface heat fluxes are very sensitive to the radiative properties of stratocumulus clouds and that a realistic simulation of both the geographical distribution of stratocumulus clouds and their optical properties is crucial.
... In the Subduction Experiment and PIRATA, we use the 5-day running mean data (thus to eliminate the high-frequency variability) for temporal variability comparisons. Throughout this section, the multitaper method (MTM) of spectral analysis (Mann and Park 1993; Mann and Lees 1996) is employed to characterize the temporal variability of surface fields and the temporal coherence relationship between NWP analyses and buoy data. MTM is a technique designed to isolate signals in time series with a characteristic noise background, which is estimated by a ''robust'' procedure that is largely unbiased by the presence of signals embedded in the noise. ...
Surface meteorological variables and turbulent heat fluxes in the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalyses 1 and 2 (NCEP1 and NCEP2) and the analysis from the operational system of the European Centre for Medium-Range Weather Forecasts (ECMWF) are compared with high-quality moored buoy observations in regions of the Atlantic including the eastern North Atlantic, the coastal regions of the western North Atlantic, and the Tropics. The buoy latent and sensible heat fluxes are determined from buoy measurements using the recently improved Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) flux algorithm.The time mean oceanic heat loss from the model analyses is systematically overestimated in all the regions. The overestimation in latent heat loss ranges from about 14 W m2 (13%) in the eastern subtropical North Atlantic to about 29 W m2 (30%) in the Tropics to about 30 W m2 (49%) in the midlatitude coastal areas, where the overestimation in sensible heat flux reaches about 20 W m2 (60%). Depending upon the region and the NWP model, these systematic overestimations are either reduced, or change to underestimations, or remain unchanged when the TOGA COARE flux algorithm is used to recalculate the fluxes. The bias in surface meteorological variables, one of the major factors related to the biases in the revised NWP heat fluxes, varies with region and NWP analysis. Generally the temperature and humidity biases in the coastal regions are much larger than other regions. In the extratropical regions, NCEP1 and NCEP2 generally show a wet bias, which is mainly responsible for the underestimation in the revised NWP latent heat loss. In the Tropics a dry bias is found in the NWP analyses, particularly in ECMWF and NCEP2, which contributes to the overestimation in the revised NWP latent heat loss. Compared to NCEP1, NCEP2 shows less cold bias in 2-m air temperature and thus less biased sensible heat flux; NCEP2 also shows less humid bias in 2-m humidity in the extratropical regions but more dry bias in 2-m humidity in the Tropics, either of which leads to a more biased latent heat flux in NCEP2.Despite the significant biases in the NWP surface fields and the poor representation of short-time sea surface temperature variability, the NWP models are able to represent the dominant short-time variability in other basic variables and thus the variability in heat fluxes in the wintertime coastal regions of the western North Atlantic (on timescales of 3-4 days and 1 week) and the northern and southern subtropical regions (on a timescale of about 2 weeks), but ECMWF and particularly the NCEP analyses do not represent well the 2-3-week variability in the tropical Atlantic.
... [2] Interdecadal climate variability, a fluctuation added to long-term climatic trends, is the background information influencing interannual climate variability [Nakamura et al., 1997;Moron et al., 1998;Minobe and Mantua, 1999]. Observational evidence for the interdecadal variability of the atmosphere-ocean system has attracted more and more attention over the past decade [Trenberth, 1990;Mann and Park, 1993;Graham et al., 1994;Latif and Barnett, 1994;Trenberth and Hurrell, 1994;Tourre et al., 1999aTourre et al., , 1999b. The impact of the interdecadal variability of the atmosphere-ocean system on climate variability in the regions surrounding the North Pacific has been increasingly documented [Latif and Barnett, 1994;Mantua et al., 1997]. ...
The interdecadal variability of summer precipitation in Beijing from 1724 to 2005 is analyzed using a filter, keeping the true trends at time series ends. A probability distribution, Pearson type III, was applied to the summer precipitation series to estimate the probability of anomalous rainfall. This study includes the correlation between the interdecadal variations of the summer precipitation in Beijing and those of the indices of Northern Atlantic Oscillation (NAO), Southern Oscillation (SOI), Pacific Decadal Oscillation (PDO), and summer monsoon (SMS) of East Asia indices are computed. A methodology is thus developed to forecast the probable distribution of precipitation intensities in Beijing. Results show that the probability of drought in Beijing has greatly increased since the middle of the 1960s. The interdecadal variability of NAO, PDO, and SMS are extremely important for the low-frequency forecast of anomalous summer rainfall in Beijing. The method developed here seems appropriate to estimate the probability of future anomalous summer rainfall.
... Additionally, the multiple-taper spectral domain method (MTM) (Mann and Park 1999) is also used to detect and reconstruct the signals. The MTM employs a small set of orthogonal data tapers to describe phase and amplitude modulated structures (Mann and Park 1993). The tapers are the discrete set of eigenfunctions that solve the variational problem of minimizing leakage outside of a frequency band with half bandwidth equal to pf R, where f R =1/(NΔt) is the Rayleigh frequency, N is the length of series, Δt is the sampling interval, and p is a bandwidth parameter. ...
The wind-driven circulation in the northwestern Pacific and the South China Sea (SCS) is simplified as a two-layer, quasi-geostrophic
model in two rectangular basins connected by an idealized strait. This model is used to investigate the impact of the western
boundary current (WBC) on the adjacent marginal sea. The variability of the circulation in the two basins is investigated
with a high resolution and at low viscosity, which allows the numerical solution to resolve mesoscale eddy forcing. The model
ocean is driven by the time-independent asymmetric wind stress acting on the idealized Pacific (large basin) only. Under the
reference parameters used in this study, the WBC can intrude into the idealized SCS (small basin) in the form of a loop current,
shedding eddies regularly. The rate of eddy shedding is nearly constant throughout the entire integration time of the model;
however, the intensity of the eddy-shedding exhibits multiple timescale variability ranging from quasi-biennial to decadal
timescale. A set of sensitivity experiments demonstrate that our results are robust against changes to model parameters and
geometry. Multivariate spectral analysis is used to extract the spatiotemporal feature of the variability. Joint analysis
for the two basins shows that the circulation in the idealized SCS is significantly impacted by the variability at decadal
(15-year), interannual (5–7-year and quasi-biennial), and quasi-annual timescales. The spatial structures of the modes of
variablility suggest that the variance in position of the WBC, combined with mesoscale activity, act to influence the low-frequency
modes of the idealized SCS. The structural differences between the modes strongly impacting the idealized SCS and those having
weak influence are also presented.
... BARCAST infers a spatial correlation length scale, calculated as 1/f, of about 3300 km, which is larger than the 1700 and 1500 km estimated by Hansen and Lebedeff (1987) and Mann and Park (1993), respectively. The estimates from those studies are in line with the 1800 km derived from the global CRU dataset (Fig. 2). ...
Reconstructing the spatial pattern of a climate field through time from a dataset of overlapping instrumental and climate proxy time series is a nontrivial statistical problem. The need to transform the proxy observations into estimates of the climate field, and the fact that the observed time series are not uniformly distributed in space, further complicate the analysis. Current leading approaches to this problem are based on estimating the full covariance matrix between the proxy time series and instrumental time series over a “calibration” interval and then using this covariance matrix in the context of a linear regression to predict the missing instrumental values from the proxy observations for years prior to instrumental coverage.
A fundamentally different approach to this problem is formulated by specifying parametric forms for the spatial covariance and temporal evolution of the climate field, as well as “observation equations” describing the relationship between the data types and the corresponding true values of the climate field. A hierarchical Bayesian model is used to assimilate both proxy and instrumental datasets and to estimate the probability distribution of all model parameters and the climate field through time on a regular spatial grid. The output from this approach includes an estimate of the full covariance structure of the climate field and model parameters as well as diagnostics that estimate the utility of the different proxy time series.
This methodology is demonstrated using an instrumental surface temperature dataset after corrupting a number of the time series to mimic proxy observations. The results are compared to those achieved using the regularized expectation–maximization algorithm, and in these experiments the Bayesian algorithm produces reconstructions with greater skill. The assumptions underlying these two methodologies and the results of applying each to simple surrogate datasets are explored in greater detail in Part II.
Persistent fluctuations in the latitudinal position of the North Atlantic (NATL) jet stream are closely linked to extreme weather anomalies, particularly over Europe. Accurately representing jet stream persistence in climate models is essential for enhancing the reliability of future regional extreme weather projections. This study investigates the summer persistence of the NATL jet stream latitudinal fluctuations and the Summer North Atlantic Oscillation (SNAO) using data from CMIP6 models and ERA5 reanalysis. Our findings reveal that CMIP6 models generally overestimate persistence compared to ERA5 during the historical period. Utilizing the relative vorticity tendency equation, we assess the strength of the eddy‐mean flow feedback and identify a positive relationship between persistence and feedback strength across models. We also found that a large fraction of the intermodel spread in precipitation persistence is associated with differences in the persistence of jet fluctuations.
We analyze the transitions between established phases of the El Niño Southern Oscillation (ENSO) by surveying the daily data of the southern oscillation index from an entropic viewpoint using the framework of stochastic statistical physics. We evaluate the variation of entropy produced due to each recorded path of that index during each transition as well as taking only into consideration the beginning and the end of the change between phases and verified both integral fluctuation relations. The statistical results show that these entropy variations have not been extreme entropic events; only the transition between the strong 1999–2000 La Niña to the moderate 2002–2003 El Niño is at the edge of being so. With that, the present work opens a long and winding avenue of research over the application of stochastic statistical physics to climate dynamics.
Constraining unforced and forced climate variability impacts interpretations of past climate variations and predictions of future warming. However, comparing General Circulation Models (GCMs) and Last Millennium Holocene hydroclimate proxies reveals significant mismatches between simulated and reconstructed low-frequency variability at multi-decadal and longer timescales. This mismatch suggests that existing simulations underestimate either external or internal drivers of climate variability. In addition, large differences arise across GCMs in both the magnitude and spatial pattern of low-frequency climate variability.
Dynamical understanding of forced and unforced variability is expected to contribute to improved interpretations of paleoclimate variability. To that end, we develop a framework for fingerprinting spatiotemporal patterns of temperature variability in forced and unforced simulations. This framework relies on two frequency-dependent metrics: (1) degrees of freedom (≡ N ) and (2) spatial coherence. First, we use N and spatial coherence to characterize variability across a suite of both pre-industrial control (unforced) and last-millennium (forced) GCM simulations. Overall, we find that, at low frequencies and when forcings are added, regional independence in the climate system decreases, reflected in fewer N and higher coherence between local and global-mean surface-temperature. We then present a simple three-box moist-static-energy-balance model for temperature variability, which is able to emulate key frequency-dependent behavior in the GCMs. This suggests that temperature variability in the GCM ensemble can be understood through Earth’s energy budget and down-gradient energy transport, and allows us to identify sources of polar-amplified variability. Finally, we discuss insights the three-box model can provide into model-to-model GCM differences.
In karst terrains, fractures and conduits often occur in clusters, forming groundwater quick flow belts, which are the major passages of groundwater and solute transport. We propose a cost-effective method that utilizes precipitation and spring discharge data to identify groundwater quick flow belts by the multitaper method (MTM). In this paper, hydrological processes were regarded as the transformation of precipitation signals to spring discharge signals in a karst spring catchment. During the processes, karst aquifers played the role of signal filters. Only those signals with high energy could penetrate through aquifers and reflect in the spring discharge, while other weak signals were filtered out or altered by aquifers. Hence, MTM was applied to detect and reconstruct the signals that penetrate through aquifers. Subsequently, by analyzing the reconstructed signals of precipitation with those of spring discharge, we acquired the hydraulic response time and identified the quick flow belts. Finally, the methods were applied to the Niangziguan Spring (NS) catchment, China. Results showed that the hydraulic response time of the spring discharge to precipitation was 3 months at Pingding County; 4 months at Yuxian County, Yangquan City, Xiyang County, and Heshun County; and 27 months at Shouyang County and Zouquan County. These results suggested that Pingding County is located at a groundwater quick flow belt, which is a major passage of groundwater and contaminants, in the NS catchment. This is important since Pingding County is not only the key development area of karst groundwater but also the key conservation area for sustainable development of karst groundwater resources in NS catchment.
This chapter reviews both climatic change and climatic variability in the Southern Hemisphere. While its scope concentrates on the changes and processes that have occurred during the twentieth century, particularly since 1950, it also attempts to bring together much paleoclimatic data and consider whether “pseudo-cyclic” phenomena, such as the El Niño-Southern Oscillation, have influences on longer timescales.
Paleoclimatic data provide our only real estimates of past climatic variability on the decadal-to-century timescale for the last few millenia. Here we consider, through analyses of the instrumental data, how many evenly-spaced reconstructions would be required to estimate continental and hemispheric-scale average temperatures. The number required depends on the timescale of interest with fewer required the longer the timescale. The ability of paleoclimatic reconstructions to record faithfully the course of climate variability similarly on all timescales is briefly considered.
The widespread influence of El Niño-Southern Oscillation (ENSO) phases on regional climate is well known to contribute to climate anomalies around the world. Understanding the effects of climate variability given the ENSO phases is an important component to improve crop management and reduce climate risk due to potential changes in temperature and precipitation patterns. Recognizing the spatial structure in precipitation and temperature under different ENSO phases is fundamental for comprehensive environmental assessments through decisions and policies that consider climate variability at regional scales. The objective of this study was to investigate if there is evidence of changes to the spatial structure of precipitation and temperature associated with the three categories of ENSO phases: El Niño, La Niña and neutral years in two study areas, the Southeast (Alabama, Florida and Georgia) and the Midwest (Nebraska) United States. Daily data of maximum temperature, minimum temperatures and precipitation (1981-2010) from 407 weather stations were analysed. The spatial structure was measured by analysing the monthly correlation matrices calculated from daily observations. To determine the potential changes to spatial structures of precipitation and temperature, the spatial structure was compared with using the complete 30 year period divided by the three categories of the ENSO phases. The results showed statistically significant differences in the spatial structures of maximum and minimum temperature and precipitation (amount and distribution) among the different ENSO phases and between the combinations of two kinds of different ENSO phases. Statistically significant changes in spatial correlation at seasonal and monthly timescales among the different ENSO phases were also observed in both regions. The statistical differences were not uniform in both regions, and some region-variable-month combinations showed no significance. Knowledge of spatial structure among some combinations of different ENSO phases at each region would be useful to improve further applications of weather/climate data in other disciplines such as geo-spatial weather generator.
Orbital floating time scales are proposed for the Valanginian Stage and part of the Hauterivian Stage (Early Cretaceous). These are based on the identification of the eccentricity cycles from spectral analyses performed on high-resolution climatic proxies measured on hemipelagic marl-limestone alternations. Five reference sections were analysed in the Vocontian Basin (SE France), spanning the entire Valanginian. A duration of 5,08 myr is proposed for the Valanginian Stage from the identification of the 405-kyr eccentricity cycle. The time frame proposed, combined with available radiometric ages, shows that the mid-Valanginian 13C positive excursion (namely the Weissert Event) occurs prior to the onset of the Paraná-Etendeka traps. The stronger expression of the obliquity cycles in the upper part of the Valanginian Stage may be caused by the onset of low-extension polar ice. The Hauterivian-Barremian transition of the Río Argos section (SE Spain) was studied by a multi-proxies analysis (clay minerals, magnetic susceptibility or MS). Compared to limestone beds, marl interbeds are enriched in kaolinite and illite, impoverished in smectite and show stronger MS values. This reflect tropical humid conditions during marl deposits while limestone were deposited under semi arid conditions. The durations of the P. ohmi and T. hugii ammonite zones are assessed at 0.78 myr and 0.54 myr, respectively. The duration of the Faraoni anoxic event ranges from 100 to 150 kyr. By correlation with other sections, the Río Argos section appears to be the most valuable candidate for GSSP.
Lake Urmia, the second largest hyper-saline lake on earth, has recently experienced a dramatic water level reduction. This could have been caused by climate change or other anthropogenic effects; however it could also be a part of natural climate variability. To explore the hydroclimate variability effect on the lake water level, two tele-connections were considered for analyses; Southern Oscillation Index (SOI) and Northern Atlantic Oscillation (NAO). Spectral and coherency analysis were used to recognize the frequency components and relationship between the teleconnections and the lake water level fluctuations. The results show that the recent water level fall and the rise of water level in 1994–1999 cannot be explained by natural periodic behavior of Lake Urmia. The inter-decadal water level oscillations are coherent with NAO and SOI components of such oscillations. The anthropogenic effect on the lake water level was also explored using non-parametric trend analysis. The results show that the lake water level has a positive trend between 1966 and 1995, but the trend is not significant at a 95% confidence level. On the other hand, the trend between 1995 and 2009 is negative and it is significant at a 99% confidence interval. This study shows that the very recent water level fall is due to anthropogenic impacts rather than natural variability.
State-space statistical models are used to decompose time series of oceanic parameters from the coastal Northeast Pacific Ocean into a non-parametric trend term, a nonstationary seasonal component, and a stationary autoregressive component. Climate scale variations in upwelling, sea surface temperature, and wind stress are examined, and regional differences in the component series on decadal scales are explored.
Using 92-year precipitation data from 400 rain gauge stations located in 48 states throughout the continental United States, the change in precipitation in space and time was investigated. The variability in precipitation was investigated using an entropy-based approach. The Mann-Kendall, Spearman's rho, and Sen slope tests were applied to assess the existence of a trend in precipitation. Analysis showed that annual precipitation exhibited lower temporal variability than did its constituent seasonal series. The fall precipitation had the highest variability, and the spring precipitation the lowest. Not many stations exhibited trends, and they are concentrated in limited areas of the United States. The greatest part of those exhibiting statistically significant trends showed increasing trends both in precipitation and rainy days. Only in a few cases negative trends were found. Finally, analysis showed that no relationship can be established between trend and variability in precipitation. DOI: 10.1061/(ASCE)HE.1943-5584.0000677. (C) 2013 American Society of Civil Engineers.
Interannual variability in the southern and equatorial Atlantic is investigated using an atmospheric general circulation model (AGCM) coupled to a slab ocean model (SOM) in the Atlantic in order to isolate features of air–sea interactions particular to this basin. Simulated covariability between sea surface temperatures (SSTs) and atmosphere is very similar to the observed non-ENSO-related covariations in both spatial structures and time scales. The leading simulated empirical coupled mode resembles the zonal mode in the tropical Atlantic, despite the lack of ocean dynamics, and is associated with baroclinic atmospheric anomalies in the Tropics and a Rossby wave train extending to the extratropics, suggesting an atmospheric response to tropical SST forcing. The second non-ENSO mode is the subtropical dipole in the SST with a mainly equivalent barotropic atmospheric anomaly centered on the subtropical high and associated with a midlatitude wave train, consistent with atmospheric forcing of the subtropical SST.
The power spectrum of the tropical mode in both simulation and observation is red with two major interannual peaks near 5 and 2 yr. The quasi-biennial component exhibits a progression between the subtropics and the Tropics. It is phase locked to the seasonal cycle and owes its existence to the imbalances between SST–evaporation and SST–shortwave radiation feedbacks. These feedbacks are found to be reversed between the western and eastern South Atlantic, associated with the dominant role of deep convection in the west and that of shallow clouds in the east. A correct representation of tropical–extratropical interactions and of deep and shallow clouds may thus be crucial to the simulation of realistic interannual variability in the southern and tropical Atlantic.
This chapter introduces a methodology for signal detection and reconstruction of irregular spatiotemporal oscillatory signals—the multiple-taper spectrum estimation method (MTM)–singular-value decomposition (SVD) methodology. This methodology is offered as an alternative technique which avoids most of the problems encountered in traditional techniques and provides an efficient exploratory method for climate signal detection. The associated signal-detection parameter—the local fractional variance spectrum (LFV) spectrum—yields the correct null distribution for a very general class of spatiotemporal climate noise processes and the correct inferences when signals are present. The methodology allows for a faithful reconstruction of the arbitrary spatiotemporal patterns of narrowband signals immersed in spatially correlated noise. The results of the MTM–SVD approach are robust to the temporal and spatial sampling inhomogeneities that are common in actual climate data. Applied to observational climate data, the MTM–SVD analysis yields insight into secular trends, low-frequency, and high-frequency quasi-oscillatory variations in the climate system. The dominant mode of secular variation has been a long-term global warming trend associated with some anomalous atmospheric circulation patterns that show similarity to the modeled response of the climate to increased greenhouse gases.
The observed anomaly of June 1988, a wave train with a persistent ridge in the north-central United States and a northward shifting of the jet stream in the Pacific-North America area, is very well simulated in each of the integrations. All three experiments were repeated using the same initial conditions, but with climatological SST. The wave train generated is similar to that in the control experiments, but it is not as robust. The simulated jet streams are also similar to those in the control experiments. Two experiments with the 1988 SSTA, but with initial conditions of 22 May 1987 and 22 May 1989 were also run. A barotropic analysis was done to obtain the normal modes associated with the 300-mb streamfunction of the June climatology. The analysis indicates the existence of a slowly growing mode with structure similar to the anomalies of 1988. -from Authors
ENSO teleconnections were originally regarded as a single train of stationary Rossby waves generated by a compact region of enhanced (reduced for La Niña) equatorial convective heating. While more recent studies have greatly enhanced this dynamical picture, the dominant conceptual model of the teleconnections still identifies this monopolar convective heat source as the ultimate driver of the teleconnections.This note presents evidence that the surrounding regions of diabatic cooling are just as important as equatorial heating in producing the ENSO teleconnections. In simulations with a linear diagnostic model, heating and cooling anomalies derived from the National Centers for Environmental Prediction National Center for Atmospheric Research (NCEP NCAR) reanalysis make comparable contributions to the upper-level eddy height anomalies. In particular, remote cooling is just as important as local heating in determining the central longitude of the subtropical El Niño anticyclones.The same diagnosis is applied to the ENSO response of an atmospheric general circulation model (AGCM) forced by observed sea surface temperatures in an integration performed by the NASA Seasonal-to-Interannual Prediction Project (NSIPP). Despite differences in the climatological basic state and diabatic heating, positive and negative heating anomalies play the same complimentary roles for the simulated ENSO response as they do for the observed ENSO pattern.
Interannual SST variability in a coupled atmosphere-mixed layer ocean model is investigated. This model has no El Niño but shows a large interannual SST variability in the tropical Pacific. The basin-scale feature of SST variation has some common characteristics shared with that obtained by a global ocean-atmosphere coupled GCM and observational data in the subtropical to the midlatitude Pacific. Both the latent heat flux and shortwave radiation have their roles in producing the SST anomalies. There is no large contrast in the total heat flux between the eastern and the western Pacific. However, their main components, the shortwave radiation and the latent heat flux, have a remarkable contrast between the cold tongue in the east and the warm pool region in the west. In the east, the ocean is warmed by shortwave radiation and cooled by latent heat. This shortwave radiation is negatively correlated with low-level clouds. When the SST is warmer than normal in the eastern Pacific, there is less low-level stratus cloud cover and more shortwave radiation reaching the surface. In the western Pacific, the ocean is warmed by less evaporation due to weaker winds. When the ocean becomes warm, it is cooled by less shortwave radiation due to stronger activity in cumulus convection.
Low-frequency (interannual or longer period) climatic variability is of interest because of its significance for the understanding and prediction of protracted climtic anomalies. Closed basin lakes are sensitive to long-term climatic fluctuations and integrate out high-frequency variability. It is thus natural to examine the records of such lakes to better understand long-term climate dynamics. Here we use singular spectral analysis and multitaper spectral analysis to analyze the time series of Great Salt Lake (GSL) monthly volume change from 1848 to 1992 and monthly precipitation, temperature, and streamflow for nearby stations with 74 or more years of data. This analysis reveals high fractional variance in 15-18, 10-12, 3-7 and 2-year frequency bands, which seems to be consistent across time series. The putative decadal and interdecadal signals appear to be related to large-scale climate signals. The interannual signals are consistent with El Niño Southern Oscillation and quasi-biennial variability. Prospects for improved prediction of the GSL volume and of protracted wet/dry periods in the western United States are discussed. .
Spectral estimation procedures which employ several prolate spheroidal sequences as tapers have been shown to yield better than standard single-taper spectral analysis when used on a variety of engineering data. We apply the adaptive multitaper spectral estimation method of Thomson (1982) to a number of high-resolution digital seismic records and compare the results to those obtained using standard single-taper spectral estimates. Single-taper smoothed-spectrum estimates are plagued by a trade-off between the variance of the estimate and the bias caused by spectral leakage. Applying a taper to reduce bias discards data, increasing the variance of the estimate. Using a taper also unevenly samples the record. Throwing out data from the ends of the record can result in a spectral estimate which does not adequately represent the character of the spectrum of nonstationary processes like seismic waveforms. For example, a discrete Fourier transform of an untapered record (i.e., using a boxcar taper) produces a reasonable spectral estimate of the large-amplitude portion of the seismic source spectrum but cannot be trusted to provide a good estimate of the high frequency roll-off.A discrete Fourier transform of the record multiplied by a more severe taper (like the Hann taper) which is resistant to spectral leakage leads to a reliable estimate of high-frequency roll-off, but this estimate weights the analyzed data unequally. Therefore single-taper estimators which are less affected by leakage not only have increased variance but also can misrepresent the spectra of nonstationary data. The adaptive multiplier algorithm automatically adjusts between these extremes. We demonstrate its advantages using 16-bit seismic data recorded by instruments in the Anza Telemetered Seismic Network. We also present an analysis demonstrating the superiority of the multitaper algorithm in providing low-variance spectral estimates with good leakage resistance which do no overemphasize the central portion of the record.
A new compilation of monthly mean surface air temperature for the Northern Hemisphere for 1851-1984 is presented based on land-based meteorological station data and fixed-position weather ship data. This compilation has been included, thus improving both spatial and temporal coverage. Second, the station data have been analyzed to assess their homogeneity. Only reliable or corrected station data have been used in calculating are averages. Grid point temperature estimates have been made by interpolating onto a 5° latitude by 10° longitude grid for each month of the 134 years. In the period of best data coverage, 58% of the area of the Northern Hemisphere is covered by the available data network. (The remaining area is mainly ocean too far from land based stations to warrant extrapolation.) The reliability of hemisphere estimates is assessed for earlier periods when coverage is less than this maximum. Year-to-year estimates are considered reliable back to about 1875. Estimates earlier than this are judged sufficiently good to indicate trends back to 1851. This new land-based hemisphere temperature curve is compared with recent estimates of Northern Hemisphere temperatures based on marine data. The two independent estimates agree well on the decadal time scale back to the start of the century, but important discrepancies exist for earlier times.
Eight local earthquakes were recorded during the operation of a small-aperture seismic array at Pinyon Flat, California. The site was chosen for its homogeneous granitic geology and its planar topography. Amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7. Magnitude-squared coherences were estimated for all station pairs. These estimates were highest for the P wave arrivals on the vertical component and lowest for the P wave recorded on the transverse component. At 500 m station separation the P and S waves were incoherent above 15 Hz and 10 Hz, respectively. Coherence for both the P and S waves decrease as frequency increases and as distance increases. The coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface. The results here suggest that even for sites that appear to be very similar, that is, those which are located on a planar surface within a few meters of granite bedrock, the measured seismic wavefield can be distorted substantially over scale lengths of 500 m. Coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations. Standard deviations of 10% are not sufficient for the random velocity distributions to approximate the results from the small-aperture array.
THE ability to distinguish a warming trend from natural variability is critical for an understanding of the climatic response to increasing greenhouse-gas concentrations. Here we use singular spectrum analysis1 to analyse the time series of global surface air tem-peratures for the past 135 years2, allowing a secular warming trend and a small number of oscillatory modes to be separated from the noise. The trend is flat until 1910, with an increase of 0.4 °C since then. The oscillations exhibit interdecadal periods of 21 and 16 years, and interannual periods of 6 and 5 years. The interannual oscillations are probably related to global aspects of the El Niño-Southern Oscillation (ENSO) phenomenon3. The interdecadal oscillations could be associated with changes in the extratropical ocean circulation4. The oscillatory components have combined (peak-to-peak) amplitudes of >0.2 °C, and therefore limit our ability to predict whether the inferred secular warming trend of 0.005 °Cyr-1 will continue. This could postpone incontrovertible detection of the greenhouse warming signal for one or two decades.
Paltridge and Woodruff1 found a warming of global mean sea-surface temperatures (SSTs) of ~1°C in the first half of the present century, but there are doubts about its reality because spurious temperature fluctuations can arise from changes in measuring instruments2,3 and because inter-annual fluctuations may contain sufficient variance to allow the observed inter-decadal variations to fall within the limits of sampling error of a stationary series3. We present here the results of analyses of worldwide SSTs and night near-surface marine air temperature (MAT) for the period 1856–1981 with the aim of estimating the magnitudes of recent climatic fluctuations of temperature at the ocean surface, taking account of changes in observing procedures. Our results show a worldwide temperature fluctuation of range ≃0.6 °C (in broad agreement with a preliminary analysis of global SST2), with the coldest period being centred around 1905–10 and the warmest occurring in the 1940s. The fluctuation has a similar magnitude to, and is nearly in phase with, climatic warmings and coolings near the surface of the Northern Hemisphere land masses for the period after 1900. Before 1900 the trends are sharply different.
The paleoclimatic variability at frequencies ranging from 10–4 cycle per year (cpy) to 10–5 cpy is investigated using a set of four deep-sea cores from the Atlantic, Pacific and Indian Oceans. Dominant features are the presence of orbital frequencies corresponding to mean periods of 117.7, 43.6, 24.9 and 19.3 kyr. These are statistically significant according to such advanced spectral tools as Blackman-Tukey, maximum entropy and the highly efficient Thomson technique. However, the main purpose of this paper is methodological, describing the statistical analyses of time series with modern methods in order to stress their relative power, advantages and disadvantages. The more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements, including combination tones. Three frequency bands of high paleoclimatic variability centred at 15.4, 13 and 10.8 kyr are indeed also detected. These two last periods are very close to those predicted by the climatic non-linear model of Ghil and Le Treut and found by Pestiaux et al. and Yiou et al.
In the choice of an estimator for the spectrum of a stationary time series from a finite sample of the process, the problems of bias control and consistency, or "smoothing," are dominant. In this paper we present a new method based on a "local" eigenexpansion to estimate the spectrum in terms of the solution of an integral equation. Computationally this method is equivalent to using the weishted average of a series of direct-spectrum estimates based on orthogonal data windows (discrete prolate spheroidal sequences) to treat both the bias and smoothing problems. Some of the attractive features of this estimate are: there are no arbitrary windows; it is a small sample theory; it is consistent; it provides an analysis-of-variance test for line components; and it has high resolution. We also show relations of this estimate to maximum-likelihood estimates, show that the estimation capacity of the estimate is high, and show applications to coherence and polyspectrum estimates.
The largest increases in surface temperatures over the Northern Hemisphere in the decade prior to 1988 were in Alaska, while substantial decreases occurred in the North Pacific Ocean. This illustrates the considerable geographic spatial structure to interdecadal temperature variations associated with changes in the atmospheric circulation. In particular, from 1977 to 1988, there was a deeper and eastward-shifted Aleutian low-pressure system in the winter half year, which advected warmer and moister air into Alaska and colder air over the North Pacific. Associated changes in surface-wind stress and wind-stress curl altered the North Pacific Ocean currents, as revealed by the Sverdrup transport. The North Pacific changes appear to be linked through teleconnections to tropical atmosphere-ocean interactions and the frequency of El Niño versus La Niña events. Consequently, the question of why it was so warm in Alaska becomes changed to one of why there were three tropical Pacific Warm Events, but no Cold Events, from 1977 to 1988, and whether changes in El Niño frequency will be altered during climate change. At the very least, these linkages and the resulting strongly regional structure of surface-temperature variations complicate any search for a greenhouse effect and global warming.
We investigate the “typical” global and large-scale regional precipitation patterns that are associated with the El Nino/Southern Oscillation (ENSO). Monthly precipitation time series from over 1700 stations are analyzed using an empirical method designed to identify regions of the globe that have precipitation variations associated with ENSO. Monthly mean ranked precipitation composites are computed over idealized 2-year ENSO episodes for all stations that include data for at least five ENSOs. The amplitude and phase of the Arm harmonic fitted to the 24-month composite values are plotted in the form of a vector for each station. When plotted on a global map, these vectors reveal both the regions of spatially coherent ENSO-related precipitation and the phase of this signal in relation to the evolution of the composite episode. Time cries of precipitation for the coherent regions identified in the harmonic vector map are examined to determine the magnitudes of the ENSO-related precipitation and th...
Data from a 63-station radiosonde network are used to estimate the variation in global tropospheric (850-300 mb) temperature between 1958 and 1989. The annual temperature was a maximum in 1988, 0.42C above the 1958-88 mean. However, the 1989 value is indicated to be only 0.12C above this mean. During 1958-88, there has been a correlation of 0.76 (significant at the 0.1% level) between annual values of global tropospheric-temperature deviation and annual values of sea-surface temperature (SST) deviation in eastern equatorial Pacific two seasons earlier. The associated linear-regression line indicates that an annual SST deviation of 1C in the region 12°S-2°N, 180°-90°W has been related on average to an annual global tropospheric-temperature deviation of 0.36C. The annual values of global tropospheric temperature have been adjusted based on this regression. With this adjustment, the year-to-year variability in global tropospheric temperature is halved, the increase in decadal-mean temperature between the 1960's and 1980's is reduced from 0.33C to 0.24C, the annual temperature is a maximum in 1989 (0.39C above the 31-year mean) rather than in 1988, and there is much more convincing evidence that the eruptions of Agung in 1963 and El Chichon in 1982 decreased global tropospheric temperatures by 0.2-0.3C for about 3 years.
We have composited historical hydrographic observations for the world
ocean for two pentads, 1955-1959 and 1970-1974, and have objectively
analyzed these data for the purpose of studying the temporal variability
of temperature and salinity in the North Atlantic Ocean. The subtropical
gyre (500-1300 m) of the North Atlantic was colder and fresher during
1970-1974 compared to 1955-1959. The relatively large changes in
temperature and salinity on constant-depth surfaces in the subtropical
gyre were due to upward displacements of isopycnal surfaces. At
intermediate depths the eastern portion of the subarctic gyre was also
colder and fresher during the 1970-1974 pentad. In contrast, the western
portion of the subarctic gyre exhibited higher temperatures and
salinities during 1970-1974 compared to 1955-1959. Characteristic
differences in temperature and salinity for both gyres were 0.5°C
and 0.025‰, respectively. Analysis of changes in potential
vorticity indicates that in the subtropical gyre potential vorticity
increased in all density layers above the 26.5 surface, suggesting that
convection in this region may have been shallower in 1970-1974 compared
to 1955-1959. Below the 26.5 surface, potential vorticity decreased
through the 27.3 surface, indicating that deeper than normal convection
may have formed the water masses in these layers. At 250-m depth,
relatively large changes in temperature and salinity occurred along the
line of maximum climatological mixed layer depth that extends northeast
to southwest across the North Atlantic Ocean.
The hypothesis that the increase in atmospheric CO2 is related to observable changes in the climate is tested using modern methods of time-series analysis. The results confirm that average global temperature is increasing and that temperature and atmospheric CO2 are significantly correlated over the past 30 years. Changes in CO2 content lag those in temperature by five months.
Recent homogenized near-surface temperature data over the land and
oceans of both hemispheres during the past 130 years are combined to
produce the first comprehensive estimates of global mean temperature.
The results show little trend in the nineteenth century, marked warming
to 1940, relatively steady conditions to the mid-1970s and a subsequent
rapid warming. The warmest 3 years have all occurred in the 1980s.
Publisher Summary This article is concerned with the causes of the variations in the surface temperature of the Atlantic Ocean from year to year and over longer periods. The processes, which influence the ocean temperature, are partly radiative transfers, partly heat exchange at the interface of ocean and atmosphere, and partly advective heat transfers by the ocean currents. The net radiative heat balance of the ocean is influenced by possible variations of the solar radiative output, and by the transmissivity of the atmosphere for short- and long-wave radiation. Variations in cloudiness would be the factor, most likely to influence measurably the annual radiative heat budget of the ocean. The ocean currents provide important contributions to the local heat budget, positive in the warm currents and negative in the cold currents. The changes in intensity of the oceanic circulation are mainly dictated by changes in the atmospheric circulation, and the resulting changes in the temperature field of the ocean surface must in turn, influence the thermodynamics of the atmospheric circulation. A clarification of these relationships is a prerequisite for the understanding of the mechanism of climatic change. This article will present some empirical findings, which have a bearing on those problems. Before proceeding to display the empirical findings on the large-scale ocean–atmosphere interaction, a brief outline will be given of the theories on the meteorological control of ocean currents and on the interface heat transfers.
A new compilation of monthly mean surface air temperature data for the Southern Hemisphere for 1851--1984 is presented based on land-based meteorological station data. Where possible, the station data used in the analysis have been assessed for homogeneity. Only reliable or corrected station data have been used in calculating area averages. Grid point temperature estimates have been made by interpolating onto a 5/sup 0/ lat by 10/sup 0/ long grid for each month of the 134 years. For the period of best data coverage, 32% of the area of the Southern Hemisphere is covered. The reliability of hemispheric estimates is assessed for earlier periods when coverage is less than this maximum. Year-to-year estimates are considered reliable back to about 1890 and earlier estimates can indicate trends back to the 1860s. This new hemispheric compilation is compared with estimates of Southern Hemisphere marine data, and comparisons between land and marine data for both hemispheres are made and interpreted. The data show a long-term warming trend amountng to about 0.5 /sup 0/C over the past 100 years. The 1938--65 cooling trend that is so evident in the Northern Hemisphere data shows up only as a hiatus in the long-term warming of the Southern Hemisphere, pointing towards some hemispherically specific causal mechanism.
Sea surface temperature anomalies in the tropical Atlantic Ocean are reexamined to investigate an apparent low-frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the ITCZ. Using principal components rotated by the varimax method and simple correlations of area-averaged temperatures, we show that during the 1964–88 interval SST anomalies north and south of the ITCZ are not significantly correlated. Therefore, the low-frequency variation, with an apparent decadal period observed in the SST gradient across the ITCZ during 1964–88, does not arise from temporally coherent and out-of-phase fluctuations in each hemisphere and cannot be characterized as a dipole.
Short-term variations of the elements representing the Earth's motion around the Sun and its rotation have been analyzed over the last 6000 years using 1-year steps. Their low-frequency part is compared first to the values obtained from a secular theory of the planetary long-term motion showing that they can be considered reliable enough to represent adequately the motion of the Earth over the last 5000 years. Spectral analysis of these values shows that the main periodicities are 2.67, 3.98, 5.26, 5.93, 7.9, 9.8, 11.9, 14.7, 15.8, 29, 42, 61, 122, 165 and 250 years for the eccentricity as well as for the climatic precession, with an additional component at around 930 years for the eccentricity and around 840 years for the climatic precession. Periodicities at 2.67, 3.8, 5.9, 8.0, 9.3, 11.9, 14.7, 18.6, 29, 135, 250 and 840 yr are also shown for the obliquity. Spectral analyses of the daily July mid-month insolation at 65N show essentially the same periodicities as the climatic precession and the obliquity, i.e. 2.67, 3.98, 5.92, 8.1, 11.9, 15.7, 18.6, 29, 40, 61 and around 900 years. Finally a wider analysis of the insolation pattern was performed related to the large periodicity band of the insolation time series for the solstices and the equinoxes for 7 different latitudes. In equatorial latitudes the insolation variance is largely explained by precession. But precession dominates everywhere with the obliquity signal being stronger at polar latitudes at the solstices. The amplitudes of the insolation change at these frequencies is of the order of 0.2 Wm–2 at the maximum.
MODELS predict1-3 that increasing atmospheric concentrations of greenhouse gases will result in an increase in the global mean temperature over the next few decades and beyond. It is therefore important to be able to distinguish a warming trend from natural variability in the time series of global temperatures. Recently, Ghil and Vautard4 applied singular spectrum analysis to a record of global surface air temperatures, and identified a secular warming trend and a small number of oscillatory modes. The oscillations had interdecadal periods of 21 and 16 years (attributed to changes in the extratropical ocean circulation), and interannual periods of 6 and 5 years (attributed to the El Ninõ/Southern Oscillation). Here we re-analyse the data by considering various lengths of the temperature record, and we apply singular spectrum analysis to five other temperature records (two global, three hemispheric). Our results offer no support for the presence of bidecadal oscillations in the global surface temperature records.
The paper presents the results of surface air temperature measurements from available meteorological stations for the period of 1880-1985. It is shown that the network of meteorological stations is sufficient to yield reliable long-term, decadal, and interannual temperature changes for both the Northern Hemisphere and the Southern Hemisphere, despite the fact that most stations are located on the continents. The results indicate a global warming of about 0.5-0.7 C in the past century, with warming of similar magnitude in both hemispheres. A strong warming trend between 1965 and 1980 raised the global mean temperature in 1980 and 1981 to the highest level in the period of instrumental records. Selected graphs of the temperature change in each of the eight latitude zones are included.
"The purpose of this paper is to survey a number of the technical tools and models that have found use in the study of human and other populations, and to indicate some problems of current interest. These tools and models are varied: integral equations, nonlinear oscillations, differential geometry, dynamical systems, nonlinear operation, bifurcation theory, semigroup theory, martingale theory, Markov processes, diffusion processes, branching processes, ergodic theory, prediction theory and state-space models. A fairly extensive bibliography is provided. Also an Appendix has been added describing the analysis of a classical entomological data set." (summary in FRE)
Astronomical frequency for climate research at the decadal to century time scale, Climate Dynamics Physics of Climate, Amer-ican Institute of Physics
- M F Loutre
- A Berger
- P Bretagnon
- P L Blanc
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Spectral Analysis and Time Series Global and re-gional scale precipitation patterns associated with the E1 Nino/Southern Oscillation
- M B Priestley
Priestley, M. B., Spectral Analysis and Time Series, Aca-demic Press, San Diego, 1981. Ropelewski, C. F., and Halpert, M. S., Global and re-gional scale precipitation patterns associated with the E1 Nino/Southern Oscillation, Mon. Weath. Rev., 115, 1606-1626, 1987.
Variation in global tropospheric temperature after adjustment for the E1 Nino influence A strategy for fre-quency spectra of Quaternary climate records Atlantic air-sea interactions
- J K Angell
- A Berger
- J L Melice
- L Hinnov
Angell, J.K., Variation in global tropospheric temperature after adjustment for the E1 Nino influence, 1958-1989, Geophys. Res. Left., 17, 1093-1096, 1990. Berger, A., Melice, J. L., and Hinnov, L., A strategy for fre-quency spectra of Quaternary climate records, Climate Dynamics, 5, 227-240, 1991. Bjerknes, J., Atlantic air-sea interactions, Adv. Geophys., 10, 1-82, 1964. Brillinger, D. R., Time Series, Data Analysis and Theory, Holden-Day, San Francisco, 1981. Elsner, J. B. and Tsonis, A. A., Do bidecadal oscillations exist in the global temperature record?, Nature, 353, 551-553, 1991.
Interdecadal oscillations and 6091-6131 III, Multita-per spectral analysis of high-frequency seismograms
- M Ghil
- R Vautard
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- Peixoto