[Show abstract][Hide abstract] ABSTRACT: Explosive volcanism can alter global climate, and hence trigger economic, political and demographic change. The climatic impact of the largest volcanic events has been assessed in numerous modelling studies and tree-ring-based hemispheric temperature reconstructions. However, volcanic surface cooling derived from climate model simulations is systematically much stronger than the cooling seen in tree-ring-based proxies, suggesting that the proxies underestimate cooling; and/or the modelled forcing is unrealistically high. Here, we present summer temperature reconstructions for the Northern Hemisphere from tree-ring width and maximum latewood density over the past 1,500 years. We also simulate the climate effects of two large eruptions, in AD 1257 and 1815, using a climate model that accounts explicitly for self-limiting aerosol microphysical processes. Our tree-ring reconstructions show greater cooling than reconstructions with lower spatial coverage and based on tree-ring width alone, whereas our simulations show less cooling than previous simulations relying on poorly constrained eruption seasons and excluding nonlinear aerosol microphysics. Our tree-ring reconstructions and climate simulations are in agreement, with a mean Northern Hemisphere extra-tropical summer cooling over land of 0.8 to 1.3 °C for these eruptions. This reconciliation of proxy and model evidence paves the way to improved assessment of the role of both past and future volcanism in climate forcing.
Full-text · Article · Aug 2015 · Nature Geoscience
[Show abstract][Hide abstract] ABSTRACT: The role of volcanogenic halogen-bearing (i.e. chlorine and bromine) compounds in stratospheric ozone chemistry and climate forcing is poorly constrained. While the 1991 eruption of Pinatubo resulted in stratospheric ozone loss, it was due to heterogeneous chemistry on volcanic sulfate aerosols involving chlorine of anthropogenic rather than volcanogenic origin, since co-erupted chlorine was scavenged within the plume. Therefore, it is not known what effect volcanism had on ozone in pre-industrial times, nor what will be its role on future atmospheres with reduced anthropogenic halogens present. By combining petrologic constraints on eruption volatile yields with a global atmospheric chemistry-transport model, we show here that the Bronze-Age 'Minoan' eruption of Santorini Volcano released far more halogens than sulfur and that, even if only 2% of these halogens reached the stratosphere, it would have resulted in strong global ozone depletion. The model predicts reductions in ozone columns of 20 to >90% at Northern high latitudes and an ozone recovery taking up to a decade. Our findings emphasise the significance of volcanic halogens for stratosphere chemistry and suggest that modelling of past and future volcanic impacts on Earth's ozone, climate and ecosystems should systematically consider volcanic halogen emissions in addition to sulfur emissions.
[Show abstract][Hide abstract] ABSTRACT: The response of stratospheric and mesospheric ozone in the tropics to short-term solar ultraviolet variations (i.e. 27-day solar rotational cycle) over the descending phases of two consecutive solar cycles (solar cycles 22 and 23) is investigated using daily ozone measurements (MLS on UARS and AURA, GOMOS on ENVISAT), reconstructed solar spectra variations and stratospheric chemistry-climate model calculations. Daily solar spectra are taken from the NRL-SSI solar reconstruction model. The chemistry-climate model is forced at the top by the reconstructed solar spectra, and at the surface by analyzed sea-surface temperatures and sea-ice. The solar variable for regression analysis is the UV flux at 205nm, within an atmospheric window region that is crucial for the ozone photochemistry. The same spectral analysis (cross-correlation, wavelet and fourier transform, coherence,...) is carried out on all the observations and model simulations, and for both periods. In the stratosphere, statistically significant correlation is found between around 1 and 10 hPa with a peak at about 4 hPa (~36 km) for both periods. However the ozone sensitivity to solar variations (defined as the percentage change in ozone for 1% change in solar 205nm flux) is two times weaker during the solar cycle 23 (0.2) than during the solar cycle 22 (0.4%/%). Moreover, wavelet transforms show that the magnitude and occurrence of the solar signal in ozone data is highly variable temporally and vanishes during several solar rotations. This intermittence is much more pronounced during the solar cycle 23 than during the solar cycle 22. The chemistry-climate model calculations are able to reproduce most of the features of the solar signal in tropical stratospheric ozone including the differences between the solar cycle 22 and 23. In the mesosphere, the analysis of the GOMOS data reveals a clear 27-day solar signal in ozone. The results have implications for the impact of solar variability on ozone and ultimately on climate on longer-time scales.
[Show abstract][Hide abstract] ABSTRACT: Recent works have shown how the study of stratospheric background aerosol i.e. in periods uninfluenced by major volcanic eruption seems more complex as it is now performed by more accurate means. We propose a re-analysis of Global Ozone Monitoring by Occultation of Stars GOMOS level 1b data for the period August 2002–July 2006, using the LPC2E processor algorithm, which was developed for the retrieval of aerosol extinction in the middle and upper stratosphere. The main differences with regard to the ‘official’ algorithm are the correction of chromatic scintillation, the spectral domain which has been restricted to the 400–700 nm region, the use of a Differential Optical Absorption Spectroscopy DOAS method for species retrieval, and the use of a fourth-order polynomial to reproduce the wavelength dependence of extinction. Since GOMOS observations are performed using stars of different magnitude and colour, discrepancy in signal-to-noise ratio between several profiles exists, and a data selection concerning standard deviation of aerosol extinction and other parameters becomes necessary. In the middle stratosphere, aerosol extinction profiles obtained with the LPC2E processor seem to be in better agreement with the SAGE III observations and sparse balloon-borne measurements than the ‘official products’. We present global coverage of the 500 nm extinction values from around 15–60 km, and the wavelength dependence in the 400–675 nm spectral range which gives information about the nature of the particles. The well-known layer of liquid aerosols can be observed in the lower stratosphere, where the value of extinction is greater for blue than for red wavelengths, as is typical for small droplets. In the middle stratosphere, relatively high extinction values are found, probably due to the presence of solid particles above 30 km at all latitudes. The presence of soot and interplanetary material in the middle atmosphere is discussed, as well as seasonal patterns common to the several years of analysis, such as the stratospheric cleansing of aerosols above 30 km during polar winters.
No preview · Article · Jul 2013 · International Journal of Remote Sensing
[Show abstract][Hide abstract] ABSTRACT: We present a summary of the scientific objectives, payload and mission profile of the Space Weather & Ultraviolet Solar Variability Microsatellite Mission (SWUSV) proposed to CNES and ESA (small mission).
[Show abstract][Hide abstract] ABSTRACT: We present the ambitions of the SWUSV (Space Weather and Ultraviolet Solar Variability) Microsatellite Mission that encompasses three major scientific objectives: (1) Space Weather including the prediction and detection of major eruptions and coronal mass ejections (Lyman-Alpha and Herzberg continuum imaging); (2) solar forcing on the climate through radiation and their interactions with the local stratosphere (UV spectral irradiance from 180 to 400 nm by bands of 20 nm, plus Lyman-Alpha and the CN bandhead); (3) simultaneous radiative budget of the Earth, UV to IR, with an accuracy better than 1% in differential. The paper briefly outlines the mission and describes the five proposed instruments of the model payload: SUAVE (Solar Ultraviolet Advanced Variability Experiment), an optimized telescope for FUV (Lyman-Alpha) and MUV (200–220 nm Herzberg continuum) imaging (sources of variability); UPR (Ultraviolet Passband Radiometers), with 64 UV filter radiometers; a vector magnetometer; thermal plasma measurements and Langmuir probes; and a total and spectral solar irradiance and Earth radiative budget ensemble (SERB, Solar irradiance & Earth Radiative Budget). SWUSV is proposed as a small mission to CNES and to ESA for a possible flight as early as 2017–2018.
[Show abstract][Hide abstract] ABSTRACT: Atmospheric water vapour has a very important effect on the climate and
the weather. Instruments developed last decades are providing total
columns with a very good accuracy, usually of the order of less than 10%
of relative value, but inter comparison between results has not been
fully explored because of the diversity of the origin of the instruments
(from astronomy to meteorology) and therefore, because of the diversity
of scientific teams: tropospheric water vapour experts at "Meteo
France", measurements of stratospheric minor constituents like ozone by
UV visible spectrometry, astronomers, etc.... At Observatoire de Haute
Provence, many instruments are able to measure atmospheric water vapour,
total columns and/or vertical profiles as well as rain and clouds. A
dedicated campaign DEMEVAP (DEvelopment of MEthods for remote sensing of
water VAPor) has been organized at Observatoire de Haute Provence, South
of France, in Octobre 2011 to compare and validate results of
measurements. Ground based observations were compared to satellite
observations and to meteorological analysis integrated amounts. Data
from Sophie, the very high resolution spectrometer on the astronomical
telescope of 1.96 cm; Schiamachy, GPS and SAOZ instruments as well as
NCEP and ECMWF analysis are compared. This paper presents the
instruments, followed by results as the agreement between instruments,
discussion as the sources of differences, and the conclusion.
[Show abstract][Hide abstract] ABSTRACT: Climate change is expected to increase winter rainfall and flooding in many extratropical regions as evaporation and precipitation
rates increase, storms become more intense and storm tracks move polewards. Here, we show how changes in stratospheric circulation
could play a significant role in future climate change in the extratropics through an additional shift in the tropospheric
circulation. This shift in the circulation alters climate change in regional winter rainfall by an amount large enough to
significantly alter regional climate change projections. The changes are consistent with changes in stratospheric winds inducing
a change in the baroclinic eddy growth rate across the depth of the troposphere. A change in mean wind structure and an equatorward shift of the tropospheric storm tracks relative to models with poor stratospheric resolution allows coupling with surface
climate. Using the Atlantic storm track as an example, we show how this can double the predicted increase in extreme winter
rainfall over Western and Central Europe compared to other current climate projections.
KeywordsClimate change–Europe–Stratosphere–Storm track
[Show abstract][Hide abstract] ABSTRACT: The variability of the stratospheric chemical composition occurs in a broad spectrum of timescales, ranging from day to decades. Some of this variability involves chemistry-climate interactions and is driven by well identified forcings such as the quasi-biennial oscillation (QBO), El Niño-Southern Oscillation (ENSO), volcanic aerosols, solar activity, and changes in halogen loading. The purpose of this study is to estimate the contributions of different forcings in the variability and long-term trend of the stratospheric chemical composition and to test how well 3-D chemistry-climate models (CCMs) can reproduce these relationships. The CCMs were integrated from 1960 to 2006 and forced with time-varying observations of stratospheric volcanic aerosols, solar spectra at the top of the atmosphere, sea surface temperatures (SSTs), sea ice cover (SIC) and GHGs and CFCs concentrations. In our study, we carry out multivariate regression (MLR) analyses on long time series of observations and CCM simulations using CCM forcings (quantified with proxies) as explanatory variables. The observational data is taken from the international NDACC (Network for the Detection of Atmospheric Composition Changes) data series and the CCM simulations are taken from the CCMVal-2 REF1 database. The focus is on the O3, HCl, N2O, HNO3, ClONO2, NO2, and CH4 columns. The aim is to check the consistency between observations and model simulations and identify the driving factors in the evolution of the stratosphere over several NDACC measurement sites. The MLR results for CCMs and NDACC observation are compared. Overall, there is a reasonably good agreement between model and NDACC regression results. In both datasets, a much higher fraction of the variability is explained by the proxies in the tropics than in the extratropics, in particular polar regions. For ozone, the QBO and solar signal dominate in the tropics whereas the trend signals appears to be more important in the polar regions For tracer species (N2O, CH4), the dominant term in the variance is the trend while for NO2 the variance is dominated by the aerosol effect. The results are found to be strongly dependent on the length of the data series. Sensitivity studies allow us to estimate the minimum length required for estimating reliably the influences of the various forcing.
[Show abstract][Hide abstract] ABSTRACT: The final warming of the stratospheric polar vortex at the end of northern hemisphere winter is examined in ECMWF ERA-Interim reanalysis data and an ensemble of chemistry climate models, using 20 years of data from each. In some years the final warming is found to occur first in the mid-stratosphere, and in others to occur first in the upper stratosphere. The strength of the winter stratospheric polar vortex, refraction of planetary waves, and the altitudes at which the planetary waves break in the northern extratropics lead to this difference in the vertical profile of the final warming. Years in which the final warming occurs first in the mid-stratosphere show, on average, a more negative NAO pattern in April mean sea level pressure than years in which the warming occurs first in the upper stratosphere. Thus, in the northern hemisphere, additional predictive skill of tropospheric climate in April can be gained from a knowledge of the vertical profile of the stratospheric final warming.
Full-text · Article · Sep 2011 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: Surface erythemal solar irradiance (UV-Ery) from 1960 to 2100 has been derived using radiative transfer calculations and projections of ozone, temperature and cloud change from 14 chemistry climate models (CCM), as part of the CCMVal-2 activity of SPARC. Our calculations show the influence of ozone depletion and recovery on erythemal irradiance. In addition, we investigate UV-Ery changes caused by climate changes due to increasing greenhouse gas concentrations. The latter include effects on both stratospheric ozone and cloud changes. The derived estimates provide a global picture of the likely changes in erythemal irradiance during the 21st century. Uncertainties arise from the assumed scenarios, different parameterizations - particularly of cloud effects on UV-Ery - and from the diversity in the CCM projections. The calculations suggest that relative to 1980 annually mean UV-Ery in the 2090s will be on average ~12% lower at high latitudes in both hemispheres, ~3% lower at mid latitudes, and marginally higher (~1%) in the tropics. The largest reduction (~16%) is projected for Antarctica in October. Cloud effects result in additional 2-3% reduction in UV-Ery at high latitudes, but they slightly moderate it at mid-latitudes (~1%). The year of return of erythemal irradiance to values of certain milestones (1965 and 1980) depends largely on the return of column ozone to the corresponding levels and is associated with large uncertainties mainly due to the spread of the model projections. The inclusion of cloud effects in the calculations has only a small effect of the return years. At mid and high latitudes, changes in clouds and stratospheric ozone dynamics due to greenhouse gases will sustain the erythemal irradiance at levels below those in 1965, despite the removal of ozone depleting substances. At high northern latitudes, the projected decreases in cloud transmittance towards the end of the 21st century will likely reduce the yearly average surface erythemal irradiance by up to 10% with respect to the 1960s.