Book

Arctic Climate Change: The ACSYS Decade and Beyond

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Abstract

The Arctic is now experiencing some of the most rapid and severe climate change on earth. Over the next 100 years, climate change is expected to accelerate, contributing to major physical, ecological, social, and economic changes, many of which have already begun. Changes in arctic climate will also affect the rest of the world through increased global warming and rising sea levels. The volume addresses the following major topics: - Research results in observing aspects of the Arctic climate system and its processes across a range of time and space scales - Representation of cryospheric, atmospheric, and oceanic processes in models, including simulation of their interaction with coupled models - Our understanding of the role of the Arctic in the global climate system, its response to large-scale climate variations, and the processes involved.

Chapters (10)

The previous decade and a half saw major advances in understanding of the Arctic atmosphere and the ability to project future climate states based on reanalysis datasets, field studies, and climate models. Limitations continue to be the lack of direct observations of the Arctic troposphere. The balance of evidence now argues for an anthropogenic component to Arctic change. Today, we see positive Arctic-wide temperature trends in all seasons with an Arctic amplification relative to lower latitude changes, but with strong regional modulations from natural variability. These include a positive index of the Arctic Oscillation (AO) in the early 1990s, a record negative phase of the AO during the winter of 2009/2010, and increased prominence of an Arctic Dipole (AD) climate pattern. The negative AO period showed linkages between Arctic and subarctic weather. Despite deficiencies in climate models used for the International Panel of Climate Change (IPCC), all models project increased temperatures and sea ice loss by mid-century, amplified through Arctic feedback processes.
The presence and characteristics of the relatively thin ice cover of Earth’s oceans at high latitude are important determinants of the polar climate and of the polar role in the global climate system. The focus of this chapter is the observation of sea ice. Advances in polar ocean science have been critically dependent on technology to provide the means for frequent and detailed observation of sea ice. The Arctic Climate System Study was an opportunity for a productive coordinated application of existing technology to the study of the marine cryosphere and provided impetus for the development and evaluation of new techniques. The chapter begins with a brief summary of the knowledge of global sea ice in the early 1990s and of the contemporary capabilities for sea ice observation. This introductory section is as a back drop against which to view the continued improvements in observational capability and knowledge associated with ACSYS during the 1990s. The chapter includes discussion of new developments in observational technology, of new activity in ice research and reconnaissance and of new understanding of sea ice. It has been organized around the structure of the original ACSYS science plan which had six process-oriented elements – sea ice extent and concentration, drift, thickness, export to temperate oceans, atmosphere-ice-ocean interaction, sea-ice mechanics – and one geographic element – sea ice of the southern hemisphere. The chapter concludes with a list tangible deliverables from the Arctic Climate System Study in relation to sea ice and a discussion of some key tasks for the future. These topics remain highly relevant in view of the present continued rapid rate of change in polar climate.
The chapter begins with an overview of the exploratory work done in the Arctic Ocean from the mid nineteenth century to 1980, when its main features became known and a systematic study of the Arctic Ocean evolved. The following section concentrates on the decade between 1980 and 1990, when the first scientific icebreaker expeditions penetrated into the Arctic Ocean, when large international programme were launched, and the understanding of the circulation and of the processes active in the Arctic Ocean deepened. The main third section deals with the studies and the advances made during the ACSYS decade. The section has three headings: the circulation and the transformation of water masses; the changes that have been observed in the Arctic Ocean, especially during the last decades; and the transports between the Arctic Ocean and the surrounding world ocean through the different passages, Fram Strait, Barents Sea, Bering Strait and the Canadian Arctic Archipelago. In section four, the Arctic Ocean is considered as a part of the Arctic Mediterranean Sea, and the impacts of possible climatic changes on the circulation in the Arctic Mediterranean and on the exchanges with the world ocean are discussed. KeywordsArctic Ocean-Arctic Mediterranean Sea-Ocean Circulation-Water mass formation-Water mass transformation-Mixing-Open ocean convection-Thermohaline circulation-Boundary convection-Intrusions-Double-diffusive convection
The transition between the liquid and solid phase affects all processes in the Arctic. The solid phase is a special challenge to the instruments and the scientists who develop new instruments or analyze, correct, and interpret the observed data. This chapter shows some results from observed parameters of the hydrological cycle, that is, precipitation, snow, runoff, and the atmospheric moisture flux into the polar cap. The precipitation in the Arctic catchments shows only for central Siberia a slight decreasing trend in summer and in North Europe an increasing trend in winter. In Northern Eurasia in winter, the snow depth and snow cover duration increase, as well as the temperature. The runoff and the atmospheric moisture flux derived from radiosonde data show no temporal changes. The uncertainties are still high due to the sparse measuring network, and satellite data are not yet usable for climatological purposes.
The Arctic is part of the global climate system. To address the issue of climate, the fluxes of heat, salt, and fresh water must be considered. One of the most speculated reasons for rapid climate change in the subarctic North Atlantic, and the global conveyor belt, is a breakdown of the thermohaline circulation (THC) due to an increased fresh water supply. Whitehead’s (Estuaries 21:281–293, 1998) one-box dynamic model is used to show how multiple states and catastrophe can occur in the Arctic Mediterranean with variable freshening and cooling. The broader question is how this interacts with the global climate. In this chapter, we focus on the oceanic aspects of the arctic climate system, discuss processes, review the data, and speculate on the role this part of the globe has in the greater context of global climate. The interaction with the global system comprises the outflow of freshwater and ice, and deeper, freshened, and cooled seawater into the subarctic North Atlantic, via the Labrador Sea. An example of significant climate variability in the twentieth century is presented.
This chapter summarises mesoscale modelling studies, which were carried out during the ACSYS decade until 2005. They were aiming at the parameterisation and improved understanding of processes in the Arctic boundary layer over the open ocean and marginal sea ice zones and over the Greenland ice sheet. It is shown that progress has been achieved with the parameterization of fluxes in strong convective situations such as cold-air outbreaks and convection over leads. A first step was made towards the parameterization of the lead-induced turbulence for high-resolution, but non-eddy resolving models. Progress has also been made with the parameterization of the near-surface atmospheric fluxes of energy and momentum modified by sea ice pressure ridges and by ice floe edges. Other studies brought new insight into the complex processes influencing sea ice transport and atmospheric stability over sea ice. Improved understanding was obtained on the cloud effects on the snow/ice surface temperature and further on the near-surface turbulent fluxes. Finally, open questions are addressed, which remained after the ACSYS decade for future programmes having been started in the years after 2005.
In this chapter, we provide an overview of current applications of regional climate models (RCMs) to the Arctic. There are increased applications of RCMs to present-day climate simulations and process parameterisations. Any advances in regional climate modelling must be based on analysis of physical processes in comparison with observations. In data-poor regions like the Arctic, this approach may be completed by a collaborative analysis of several research groups. Within the ARCMIP (Arctic Regional Climate Model Intercomparison Project), simulations for the SHEBA year 1997–1998 have been performed by several Arctic RCMs. The use of high resolution RCMs can contribute to a better description of important regional physical processes in the ocean, cryosphere, atmosphere, land and biosphere including their interactions in coupled regional model systems. This is based on identifying and modelling of the key processes and on an assessment of the improved understanding in the light of analysis of instrumental as well as paleoclimatic and paleoenvironmental records. The main goal is to address the deficiencies in understanding the Arctic by developing improved physical descriptions of Arctic climate feedbacks in atmospheric and coupled regional climate models and to implement the improved parameterisations into global climate system models to determine their global influences and consequences for decadal-scale climate variations. A further aim is to model the main feedbacks correctly to arrive at a more reliable estimate of future changes due to the coupling between natural and anthropogenic effects.
The interaction of sea ice with the underlying ocean is an important component of the climate system. Dynamic and thermodynamic processes determine this interaction. Whereas thermodynamic sea-ice processes have been incorporated in climate models early on, the dynamics of the sea ice has been neglected for quite some time. Therefore, a major activity during the ACSYS project was the optimization of dynamical processes in sea-ice models and the development of coupled sea-ice–ocean general circulation models.
We review the history of global climate model (GCM) development with regard to Arctic climate beginning with the ACSYS era. This was a time of rapid improvement in many models. We focus on those aspects of the Arctic climate system that are most likely to amplify the Arctic response to anthropogenic greenhouse gas forcing in the twentieth and twenty-first centuries. Lessons from past GCM modeling and the most likely near-future model developments are discussed. We present highlights of GCM simulations from two sophisticated climate models that have the highest Arctic amplification among the the models that participated in the World Climate Research Programme’s third Coupled Model Intercomparison Project (CMIP3). The two models are the Hadley Center Global Environmental Model (HadGEM1) and the Community Climate System Model version 3 (CCSM3). These two models have considerably larger climate change in the Arctic than the CMIP3 model mean by mid-twenty-first century. Thus, the surface warms by about 50% more on average north of 75∘N in HadGEM1 and CCSM3 than in the CMIP3 model mean, which amounts to more than three times the global average warming. The sea ice thins and retreats 50–100% more in HadGEM1 and CCSM3 than in the CMIP3 model mean. Further, the oceanic transport of heat into the Arctic increases much more in HadGEM1 and CCSM3 than in other CMIP3 models and contributes to the larger climate change.
The cryosphere, derived from the Greek word cryo for “cold”, is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets and permafrost and seasonally frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in global climate and in climate model response to global change. The World Climate Research Programme (WCRP) established the Climate and Cryosphere (CliC) Project in 2000 as an evolution from the Arctic Climate System Study (ACSYS) with a global focus on the cryosphere and all its components in the Earth system. The CliC Project coordinates and enables research on (a) terrestrial cryosphere and hydroclimatology of cold regions with special focus on the carbon budget and permafrost, (b) ice masses and sea level which includes ice sheets, ice caps and glaciers, (c) the marine cryosphere and climate which includes all forms of sea ice and (d) the global predictions and the cryosphere to improve the prediction for regional climate models with the inclusion of cryospheric components.
... The system of boundary currents including water from the two branches of Atlantic inflow is referred to as the Arctic Circumpolar Boundary Current (Rudels et al., 1999). However, the detailed circulation is far from one simple flow along the continental slopes of the shelves which emerges from spatial contrasts of the Atlantic layer and deep water properties (Rudels et al., 2012). The complex seafloor 15 landscape consists of extensive submarine ridges with morphologies that influence and steer the currents (Fig. 1). ...
... The bathymetric portrayal of the LR in the latest version 3.0 of the International Bathymetric Chart of 15 the Arctic Ocean (IBCAO) is mainly based on sparse single beam echo soundings from icebreakers and submarines and digitized depth contours from published maps, apart from a few areas mapped with multibeam echo sounder (Jakobsson et al., 2012). The sparse source data implies that bathymetric details of importance from an oceanographic perspective may be missed in some areas, such as the location of bathymetric passages or saddles in LR, which are critical as this is where a large part of the 20 water exchange between the basins can occur. ...
... The profiles imply that this exchange is not an organized flow in one direction but more likely interleaving motions in relatively distinct layers that can go in both directions and are probably intermittent in nature. An A 2011 Polarstern section (Schauer et al., 2012) crosses the LR at 8430'N and provides a useful complement to the SWERUS-C3 stations. It shows an AW water core that is cooler and fresher than in 20 2014 (Fig. 8). ...
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The Lomonosov Ridge represents a major topographical feature in the Arctic Ocean which has a large effect on the water circulation and the distribution of water properties. This study presents detailed bathymetric survey data along with hydrographic data at two deep passages across the ridge: A southern passage (80–81° N) where the ridge crest meets the Siberian continental slope and a northern passage around 84.5° N. The southern channel is characterized by smooth and flat bathymetry around 1600–1700 m with a sill depth slightly shallower than 1700 m. A hydrographic section across the channel reveals an eastward flow with Amundsen Basin properties in the southern part and a westward flow of Makarov Basin properties in the northern part. The northern passage includes an approximately 72 km long and 33 km wide trough which forms an intra basin in the Lomonosov Ridge morphology (the Oden Trough). The eastern side of Oden Trough is enclosed by a narrow and steep ridge rising 500–600 m above a generally 1600 m deep trough bottom. The deepest passage (the sill) is 1470 m deep and located on this ridge. Hydrographic data show irregular temperature and salinity profiles indicating that water exchange occurs as midwater intrusions bringing water properties from each side of the ridge in well-defined but irregular layers. There is also morphological evidence that some rather energetic flows may occur in the vicinity of the sill. A well expressed deepening near the sill may be the result of seabed erosion by bottom currents.
... Many works on Arctic climatic conditions and the mechanisms controlling its climatic processes have been published. An overview of the most important literature in this field can be found in, for example, Przybylak (2002); Bobylev et al. (2003); Turner and Marshall (2011); Lemke and Jacobi (2012); Serreze and Barry (2014); Przybylak (2016). ...
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The paper presents results describing the influence of Atmospheric Circulation (AC) on meteorological conditions on Kaffiøyra (NW Spitsbergen, Svalbard Archipelago) in 23 summer seasons (July 21–August 31) in the years 1975, 1977–80, 1982, 1985, 1989, 1997–2000, 2005–15.The analysis covered the diurnal sums or means of major meteorological parameters: total cloudiness, sunshine duration, air temperature, wind speed, relative air humidity, water vapour pressure, and precipitation. Extreme weather events in terms of any given parameter were defined as days whose diurnal values (mean/ sum) were in the ≤5th or ≥95th percentiles. The influence of AC on meteorological conditions on Kaffiøyra was analysed using the calendar of circulation types (CT) by T. Niedźwiedź et al. (Calendar of atmospheric circulation types for Spitsbergen-a digital dataset, 2018). In the study area, the variability of individual meteorological parameters depends primarily on air-mass advection direction, while type of baric regime is less important. Our study highlights that the greatest positive anomalies and a significant frequency of extreme values of cloudiness, wind speed, air temperature, humidity and precipitation occurred during air mass advection mainly from the SW and S. It was also demonstrated that sunshine duration correlated statistically significantly with the frequency of the anticyclonic macrotype, and precipitation with the cyclonic macrotype. The results confirmed that atmospheric circulation plays the most important role in shaping weather conditions in Spitsbergen.
... The ecosystem of the high northern latitudes is affected by the recently changing environmental conditions [1]. With regard to the regional and global implications there is a need for high resolution spatiotemporal information of the Arctic's surface and the occurring changes. ...
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In this work the potential of polarimetric Synthetic Aperture Radar (PolSAR) data of dual-polarized TerraSAR-X (HH/VV) and quad-polarized Radarsat-2 was examined in combination with multispectral Landsat 8 data for unsupervised and supervised classification of tundra land cover types of Richards Island, Canada. The classification accuracies as well as the backscatter and reflectance characteristics were analyzed using reference data collected during three field work campaigns and include in situ data and high resolution airborne photography. The optical data offered an acceptable initial accuracy for the land cover classification. The overall accuracy was increased by the combination of PolSAR and optical data and was up to 71% for unsupervised (Landsat 8 and TerraSAR-X) and up to 87% for supervised classification (Landsat 8 and Radarsat-2) for five tundra land cover types. The decomposition features of the dual and quad-polarized data showed a high sensitivity for the non-vegetated substrate (dominant surface scattering) and wetland vegetation (dominant double bounce and volume scattering). These classes had high potential to be automatically detected with unsupervised classification techniques.
... A novel aspect of this study is the analysis of lithological variability on centimetre-scales, which represents a limitation of conventional multi-proxy methods operating on decimetre to meter scales. As (Lemke and Jacobi, 2011). White stars represent core locations: 1.) LOMROG07-PC08, 2.) LOM-ROG07-PC04, 3.) LOMROG12-PC05, and 4.) AO96-B7-1 PC. ...
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Our understanding of past climate conditions in the Arctic Ocean has been hampered by poor age control caused in part by low sedimentation rates (<1 cm/kyr), hiatuses during glacial intervals as well as the scarcity and poor preservation of calcareous nanno- and microfossils in the sediments. Although recent advances using variations in single element (e.g. Mn) content or physical sediment properties (e.g. bulk density, grain size, colour) of the recovered sediments have aided Arctic core-to-core correlations, unique depositional events and post-depositional changes can complicate stratigraphic interpretations based on individual or even multiple, physical or chemical parameters. Furthermore, clear correlations between cores using physical and chemical parameters are not always possible to establish. To tackle this issue, we developed an algorithm that combines clustering and multivariate ordination to test the interrelation of multiple input parameters (e.g. an array of individual XRF elemental contents), and subsequently identifies statistically significant stratigraphic units on centimetre to decimetre scales. Our preliminary results show that a distinct sedimentological pattern during the past 45,000 years characterizes cores from the region of the Morris Jesup Rise and the Greenland side of the Lomonosov Ridge. Stratigraphic patterns of the Siberian Side of the Lomonosov Ridge yield distinct differences, thus allowing for novel insights into sedimentary processes shaping the different regions within the Arctic Ocean. We also argue that our approach can compensate for some of the weakness of single element or proxy applications, and hence aid the construction of a robust stratigraphic framework for a wide geographical range of Arctic Ocean sediments.
... Arctic snow cover dynamics offer a changing face in terms of temporal duration and water equivalent, due to recent climate change conditions (Callaghan et al., 2011;Lemke & Jacobi, 2012). Indeed, the Arctic is now experiencing some of the most rapid and severe climate change on earth. ...
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Arctic snow cover dynamics offer a changing face in terms of temporal duration and water equivalent, due to recent climate change conditions (Callaghan et al., 2011; Lemke & Jacobi, 2012). Indeed, the Arctic is now experiencing some of the most rapid and severe climate change on earth. In this context, innovative and improved methods are helpful to enhance management of the snow-pack resource for climate research, hydrology and human activities. The characteristics of Arctic snow are different from “temperate” snow (i.e. the Alps), in terms of thickness, internal structure, thermal conductivity, and metamorphism. Ground observation often indicates wind slab at the snow surface, internal rounded grains, depth hoar at the bottom, and often internal ice layer or at the Interface with ground surface (Dominé et al., 2016; Gallet et al., 2017, for spring snow). This work is part of the “Precip-A2” project (OSUG, Grenoble-France), focusing on snow and its interaction with the atmosphere, especially in terms of chemistry, radiative processes and precipitation. The application site is the Brøgger peninsula, focused on Ny-Ålesund area, Svalbard, Norway (N 78°55’ / E 11° 55’). One sub-task of the Precip-A2 project is dedicated to X-band radar measurements (ground and spaceborne) to retrieve physical properties of arctic snow.
... In temperature and salinity profiles, DC is characterized by series of step-like staircases with thick mixed layers separated by relatively thin, high-gradient interfaces. Although the DC process is expected to be present in about 14% of the global ocean [You, 2002], it mainly occurs in high latitude oceans, and plays an important role in the climate system [Lemke and Jacobi, 2011]. Recently, DC has stimulated more interests because of its impact on diapycnal mixing and sea-ice-melting in the Arctic and Antarctic oceans [Timmermans et al., 2003;Turner, 2010;Sirevaag and Fer, 2012;Zhou and Lu, 2013]. ...
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We studied the thickness of diffusive convective layers that form when a linearly stratified fluid is subjected to heating from below in the laboratory. The thickness of the bottom convecting layer is much larger than subsequent layers. These thicknesses are systematically identified and used to examine the available convecting layer thickness parameterizations, which are consisted of the measured heat flux F (or thermal buoyancy flux qT), initial stratification N, density ratio R?, thermal diffusivity ?T, etc. Parameterization with an intrinsic length scale is shown to be superior. Including the present laboratory convecting layer thicknesses and those observed in oceans and lakes, where layer thickness ranges from 0.01 to 1000 m, the parameterization is updated as , where C=38.3 for the bottom convective layer and 10.8 for the subsequent layers. Different prefactors are proposed to be attributed to different convective instabilities induced by different boundary conditions. This article is protected by copyright. All rights reserved.
... Terrestrial arthropods in Arctic and subarctic regions are exposed to extreme and variable temperatures, compared to those of most other climatic zones [1][2][3], and climate change is predicted to be especially pronounced in these regions [4,5]. In such fluctuating environments, species can adapt to their thermal environments through evolutionary changes across generations and through adaptive plasticity within the lifetime of an organism [6,7]. ...
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The ability to cope with increasing and more variable temperatures, due to predicted climate changes, through plastic and/or evolutionary responses will be crucial for the persistence of Arctic species. Here, we investigate plasticity of heat tolerance of the Greenlandic seed bug Nysius groenlandicus, which inhabits areas with widely fluctuating temperatures. We test the heat tolerance and hardening capacity (plasticity) of N. groenlandicus using both static (heat knock down time, HKDT) and dynamic (critical thermal maximum, CTmax) assays. We find that N. groenlandicus is able to tolerate short-term exposure to temperatures up to almost 50°C and that it can quickly increase heat resistance following heat hardening. Furthermore, we find that this hardening response is reversible within hours after hardening. These findings contrast with common observations from temperate and tropical insects and suggest high thermal plasticity in some Arctic insects which enables them to cope with extreme temperature variability in their habitats.
... An increasing body of scientific evidence (Lemke and Jacobi, 2012;Overland et al., 2014) details the extent of climate change in the Arctic region. The accelerating melting of the sea ice cover has received particular attention Boé et al., 2009;Deser et al., 2010;Stroeve et al., 2012;Overland and Wang, 2013). ...
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Abstract Large reductions in Arctic sea ice, most notably in summer, coupled with growing interest in Arctic shipping and resource exploitation have renewed interest in the economic potential of the Northern Sea Route (NSR). Two key constraints on the future viability of the NSR pertain to bathymetry and the future evolution of the sea ice cover. Climate model projections of future sea ice conditions throughout the rest of the century suggest that even under the most “aggressive” emission scenario, increases in international trade between Europe and Asia will be very low. The large inter-annual variability of weather and sea ice conditions in the route, the Russian toll imposed for transiting the NSR, together with high insurance costs and scarce loading/unloading opportunities, limit the use of the NSR. We show that even if these obstacles are removed, the duration of the opening of the NSR over the course of the century is not long enough to offer a consequent boost to international trade at the macroeconomic level.
... After the year 2000, Atlantic water temperatures west of Spitsbergen have been higher than the previous 100 years (Pavlov et al. 2013), and sea temperatures are expected to further increase in the Arctic in the future (Lemke and Jacobi 2012). Owing to the ongoing global warming, the Arctic sea ice has been noticeably thinner during the last few years , and the Arctic is expected to be nearly sea ice-free during summer within a few decades (Overland and Wang 2013). ...
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138 Atlantic salmon (Salmo salar) captured in the Advent Fjord off Svalbard were genetically assigned to two main clusters of European salmon. Two-thirds were assigned to salmon rivers in Finnmark (the northernmost county in Norway) and the rest to salmon rivers further south in Norway. The genetic assignment was based on genetic profiles from 60 Norwegian rivers. The two clusters correspond to two larger genetic groupings: the Barents–White seas and Atlantic groupings. Thus, we cannot rule out other populations from these groupings as sources of Atlantic salmon at Svalbard. Svalbard salmon assigned to the two genetic groupings differed in ecological and phenological traits, with highest smolt age and lowest postsmolt growth in the Finnmark salmon cluster. High smolt ages in both groups, however, suggest a northern origin of most individuals in the sample. Although Atlantic salmon have sporadically been observed in the Arctic Ocean at earlier times, the high abundance outlined here seems to be a recent phenomenon, suggesting a northward penetration caused by climate change
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The availability of highly accessible and reliable monthly gridded data sets of global land-surface precipitation is a need that was already identified in the mid-1980s when there was a complete lack of globally homogeneous gauge-based precipitation analyses. Since 1989, the Global Precipitation Climatology Centre (GPCC) has built up its unique capacity to assemble, quality assure, and analyse rain gauge data gathered from all over the world. The resulting database has exceeded 200 yr in temporal coverage and has acquired data from more than 85 000 stations worldwide. Based on this database, this paper provides the reference publication for the four globally gridded monthly precipitation products of the GPCC, covering a 111-yr analysis period from 1901-present. As required for a reference publication, the content of the product portfolio, as well as the underlying methodologies to process and interpolate are detailed. Moreover, we provide information on the systematic and statistical errors associated with the data products. Finally, sample applications provide potential users of GPCC data products with suitable advice on capabilities and constraints of the gridded data sets. In doing so, the capabilities to access El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) sensitive precipitation regions and to perform trend analyses across the past 110 yr are demonstrated. The four gridded products, i.e. the Climatology (CLIM) V2011, the Full Data Reanalysis (FD) V6, the Monitoring Product (MP) V4, and the First Guess Product (FG), are publicly available on easily accessible latitude/longitude grids encoded in zipped clear text ASCII files for subsequent visualization and download through the GPCC download gate hosted on ftp://ftp.dwd.de/pub/data/gpcc/html/download_gate.html by the Deutscher Wetterdienst (DWD), Offenbach, Germany. Depending on the product, four (0.25°, 0.5°, 1.0°, 2.5° for CLIM), three (0.5°, 1.0°, 2.5°, for FD), two (1.0°, 2.5° for MP) or one (1.0° for FG) resolution is provided, and for each product a DOI reference is provided allowing for public user access to the products. A preliminary description of the scope of a fifth product - the Homogenized Precipitation Analysis (HOMPRA) - is also provided. Its comprehensive description will be submitted later in an extra paper upon completion of this data product. DOIs of the gridded data sets examined are as follows: doi:10.5676/DWD_GPCC/CLIM_M_V2011_025 , doi:10.5676/DWD_GPCC/CLIM_M_V2011_050 , doi:10.5676/DWD_GPCC/CLIM_M_V2011_100 , doi:10.5676/DWD_GPCC/CLIM_M_V2011_250 , doi:10.5676/DWD_GPCC/FD_M_V6_050 , doi:10.5676/DWD_GPCC/FD_M_V6_100 , doi:10.5676/DWD_GPCC/FD_M_V6_250 , doi:10.5676/DWD_GPCC/MP_M_V4_100 , doi:10.5676/DWD_GPCC/MP_M_V4_250 , doi:10.5676/DWD_GPCC/FG_M_100 .
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A hierarchy of parametrizations of the neutral 10 m drag coefficients over polar sea ice with different morphology regimes is derived on the basis of a partitioning concept that splits the total surface drag into contributions of skin drag and form drag. The new derivation, which provides drag coefficients as a function of sea ice concentration and characteristic length scales of roughness elements, needs fewer assumptions than previous similar approaches. It is shown that form drag variability can explain the variability of surface drag in the marginal sea ice zone (MIZ) and in the summertime inner Arctic regions. In the MIZ, form drag is generated by floe edges; in the inner Arctic, it is generated by edges at melt ponds and leads due to the elevation of the ice surface relative to the open water surface. It is shown that an earlier fit of observed neutral drag coefficients is obtained as a special case within the new concept when specific simplifications are made which concern the floe and melt pond geometry. Due to the different surface morphologies in the MIZ and summertime Arctic, different functional dependencies of the drag coefficients on the sea ice concentration result. These differences cause only minor differences between the MIZ and summertime drag coefficients in average conditions, but they might be locally important for atmospheric momentum transport to sea ice. The new parametrization formulae can be used for present conditions but also for future climate scenarios with changing sea ice conditions.
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The availability of highly accessible and reliable monthly gridded data sets of global land-surface precipitation is a need that was already identified in the mid-1980s when there was a complete lack of globally homogeneous gauge-based precipitation analyses. Since 1989, the Global Precipitation Climatology Centre (GPCC) has built up its unique capacity to assemble, quality assure, and analyse rain gauge data gathered from all over the world. The resulting database has exceeded 200 yr in temporal coverage and has acquired data from more than 85 000 stations worldwide. Based on this database, this paper provides the reference publication for the four globally gridded monthly precipitation products of the GPCC, covering a 111-yr analysis period from 1901–present. As required for a reference publication, the content of the product portfolio, as well as the underlying methodologies to process and interpolate are detailed. Moreover, we provide information on the systematic and statistical errors associated with the data products. Finally, sample applications provide potential users of GPCC data products with suitable advice on capabilities and constraints of the gridded data sets. In doing so, the capabilities to access El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) sensitive precipitation regions and to perform trend analyses across the past 110 yr are demonstrated. The four gridded products, i.e. the Climatology (CLIM) V2011, the Full Data Reanalysis (FD) V6, the Monitoring Product (MP) V4, and the First Guess Product (FG), are publicly available on easily accessible latitude/longitude grids encoded in zipped clear text ASCII files for subsequent visualization and download through the GPCC download gate hosted on ftp://ftp.dwd.de/pub/data/gpcc/html/download_gate.html by the Deutscher Wetterdienst (DWD), Offenbach, Germany. Depending on the product, four (0.25°, 0.5°, 1.0°, 2.5° for CLIM), three (0.5°, 1.0°, 2.5°, for FD), two (1.0°, 2.5° for MP) or one (1.0° for FG) resolution is provided, and for each product a DOI reference is provided allowing for public user access to the products. A preliminary description of the scope of a fifth product – the Homogenized Precipitation Analysis (HOMPRA) – is also provided. Its comprehensive description will be submitted later in an extra paper upon completion of this data product. DOIs of the gridded data sets examined are as follows: doi:10.5676/DWD_GPCC/CLIM_M_V2011_025, doi:10.5676/DWD_GPCC/CLIM_M_V2011_050, doi:10.5676/DWD_GPCC/CLIM_M_V2011_100, doi:10.5676/DWD_GPCC/CLIM_M_V2011_250, doi:10.5676/DWD_GPCC/FD_M_V6_050, doi:10.5676/DWD_GPCC/FD_M_V6_100, doi:10.5676/DWD_GPCC/FD_M_V6_250, doi:10.5676/DWD_GPCC/MP_M_V4_100, doi:10.5676/DWD_GPCC/MP_M_V4_250, doi:10.5676/DWD_GPCC/FG_M_100.
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This article proposes an Arctic Ocean Coordinating Agreement (AOCA) as a framework for more effective coordination and sharing of practices regarding national conservation and management policies in the marine Arctic. It envisions a nimble, versatile body that operates without creating new institutions and focuses instead on convening and coordinating existing individuals and institutions whose expertise can assist the Arctic states with questions that the Arctic states define. The AOCA could incorporate aspects of regional seas agreements (RSAs) into a less formal regional arrangement that would differ significantly from traditional RSAs. Identifying the Arctic Council as the right entity to launch AOCA discussions, the article proposes that an AOCA should draw on entities already engaged in work relevant to the emerging challenges in the Arctic Ocean: the Helsinki and OSPAR Commissions, the International Council for the Exploration of the Sea (ICES), the North Pacific Marine Science Organization (PICES), and other institutions that have successfully convened appropriate sets of actors for targeted responses to shared marine management concerns around the world.
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Atmospheric humidity, clouds, precipitation, and evapotranspiration are essential components of the Arctic climate system. During recent decades, specific humidity and precipitation have generally increased in the Arctic, but changes in evapotranspiration are poorly known. Trends in clouds vary depending on the region and season. Climate model experiments suggest that increases in precipitation are related to global warming. In turn, feedbacks associated with the increase in atmospheric moisture and decrease in sea ice and snow cover have contributed to the Arctic amplification of global warming. Climate models have captured the overall wetting trend but have limited success in reproducing regional details. For the rest of the 21st century, climate models project strong warming and increasing precipitation, but different models yield different results for changes in cloud cover. The model differences are largest in months of minimum sea ice cover. Evapotranspiration is projected to increase in winter but in summer to decrease over the oceans and increase over land. Increasing net precipitation increases river discharge to the Arctic Ocean. Over sea ice in summer, projected increase in rain and decrease in snowfall decrease the surface albedo and, hence, further amplify snow/ice surface melt. With reducing sea ice, wind forcing on the Arctic Ocean increases with impacts on ocean currents and freshwater transport out of the Arctic. Improvements in observations, process understanding, and modeling capabilities are needed to better quantify the atmospheric role in the Arctic water cycle and its changes.
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A review is presented on Arctic forcing to midlatitude weather extremes and midlatitude forcing to Arctic weather extremes. Several studies have addressed the following mechanisms: reduction of the meridional temperature gradient, southward shift and weakening and increased meandering of the polar jet stream, changes in storm tracks and blocking, planetary wave trains generated by anomalous surface heating, and wave trapping due to resonance with surface forcing. These mechanisms undoubtedly affect weather extremes, but uncertainty remains on the contributions of Arctic and lower latitudes to the mechanisms. Among robust findings is that Arctic amplification contributes to the southward shift and, at least in summer, weakening of the jet stream. A major part of the Arctic tropospheric warming is, however, driven by lower latitudes. Wave trains originating from the Arctic affect summer precipitation in East Asia and northwestern Europe and winter cold spells in East Asia. North American cold winters have occurred due to amplified waves and high-latitude blockings, partly originating from warm anomalies in the Arctic. Attribution of the extremes is hampered by short datasets and small signal-to-noise ratios. Better understanding is needed on circulation response to climate change and reduction of model uncertainty.
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A laboratory experiment of two-layer diffusive convection (DC) within a rectangular cell is reported. The run-down evolution of two mixed layers and their interface is exhibited by the temperature and salinity structures, where the interface thicknesses of temperature and salinity increase with time as hT ∼ t0.42 and hS ∼ t0.43. Heat flux across the interface is respectively evaluated in terms of the heat energy conservation and the assumption of conductive interface. Both of them give the consistent heat flux values. When the 4/3 scaling between heat flux F and ΔT holds (F ∼ C(Rρ) Δ T4/3, where C(Rρ) is function of density ratio Rρ), previous heat flux parameterizations are found to have low coefficient of determination (r2 < 0.5) with our heat flux data within 1.6 < Rρ < 13.0. Heat flux is proposed to be a power-law function of Rρ, and the best fitting is C(Rρ) = 0.081(Rρ - 1)−1.28, resulting in r2 as high as 0.74. By using all available heat flux data over a wide Rρ range (1.2 ∼ 27.6), including those collected in previous literatures, C(Rρ) is revised as C(Rρ) = 0.065(Rρ - 1)−1.20 accompanied by r2 = 0.70 and reduced chi-squate Χ2 = 0.91. Alternatively, C(Rρ) can be derived from previous DC layer thickness parameterization [Guo et al., 2016], which is expressed as C(Rρ) =0.076(Rρ - 1)−4/3. This formula is also superior to previous parameterizations in the evaluation of heat flux, indicated by higher r2 and lower Χ2.
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A nonhydrostatic model (NH3D) is used for idealized dry quasi 2-D simulations of Arctic cold-air outbreaks using horizontal grid spacings between 1.25 and 60 km. Despite the idealized setup, the model results agree well with observations over Fram Strait. It is shown that an important characteristic of the flow regime during cold-air outbreaks is an ice-breeze jet (IBJ) with a maximum wind speed exceeding often the large-scale geostrophic wind speed. According to the present simulations, which agree very well with those of another nonhydrostatic mesoscale model (METRAS), the occurrence, strength, and horizontal extent L of this jet depend strongly on the external forcing and especially on the direction of the large-scale geostrophic wind relative to the orientation of the ice edge. The latter dependency is explained by the effects of the thermally induced geostrophic wind over open water and Coriolis force. It is found that coarse-resolution runs underestimate the strength of the jet. This underestimation has important consequences to the surface fluxes of heat and momentum, which are also underestimated by about 10–15% on average over the region between the ice edge and 120–180 km downstream. Our results suggest that a grid spacing of about L/7 is required (about 10–30 km) to simulate the IBJ strength with an accuracy of at least 10%. Thus, the results of large-scale models as well might contain uncertainties with regard to the simulated IBJ strength which would influence the energy budget in a large region along the marginal sea ice zones.
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