The Annual Cycle of Fractional Atmospheric Shortwave Absorption in Observations and Models: Spatial Structure, Magnitude, and Timing

2019 ◽  
Vol 32 (20) ◽  
pp. 6729-6748 ◽  
Author(s):  
M. Schwarz ◽  
D. Folini ◽  
S. Yang ◽  
M. Wild
Keyword(s):  
Water Vapor ◽  
Biomass Burning ◽  
Annual Cycle ◽  
Climate Models ◽  
Global Scale ◽  
Shortwave Radiation ◽  
Minor Role ◽  
Annual Cycles ◽  
Regional Feature ◽  
A Minor

We use the best currently available in situ and satellite-derived surface and top-of-the-atmosphere (TOA) shortwave radiation observations to explore climatological annual cycles of fractional (i.e., normalized by incoming radiation at the TOA) atmospheric shortwave absorption [Formula: see text] on a global scale. The analysis reveals that [Formula: see text] is a rather regional feature where the reported nonexisting [Formula: see text] in Europe is an exception rather than the rule. In several regions, large and distinctively different [Formula: see text] are apparent. The magnitudes of [Formula: see text] reach values up to 10% in some regions, which is substantial given that the long-term global mean atmospheric shortwave absorption is roughly 23%. Water vapor and aerosols are identified as major drivers for [Formula: see text] while clouds seem to play only a minor role for [Formula: see text]. Regions with large annual cycles in aerosol emissions from biomass burning also show the largest [Formula: see text]. As biomass burning is generally related to human activities, [Formula: see text] is likely also anthropogenically intensified or forced in the respective regions. We also test if climate models are able to simulate the observed pattern of [Formula: see text]. In regions where [Formula: see text] is driven by the annual cycle of natural aerosols or water vapor, the models perform well. In regions with large [Formula: see text] induced by biomass-burning aerosols, the models’ performance is very limited.

scholarly journals Interannual variability of tropospheric composition: the influence of changes in emissions, meteorology and clouds

2010 ◽  
Vol 10 (5) ◽  
pp. 2491-2506 ◽  
Author(s):  
A. Voulgarakis ◽  
N. H. Savage ◽  
O. Wild ◽  
P. Braesicke ◽  
P. J. Young ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Biomass Burning ◽  
Strong Influence ◽  
Transport Model ◽  
Global Scale ◽  
Meteorological Conditions ◽  
Shortwave Radiation ◽  
Chemistry Transport Model ◽  
Attribution Analysis ◽  
Emission Changes

Abstract. We have run a chemistry transport model (CTM) to systematically examine the drivers of interannual variability of tropospheric composition during 1996–2000. This period was characterised by anomalous meteorological conditions associated with the strong El Niño of 1997–1998 and intense wildfires, which produced a large amount of pollution. On a global scale, changing meteorology (winds, temperatures, humidity and clouds) is found to be the most important factor driving interannual variability of NO2 and ozone on the timescales considered. Changes in stratosphere-troposphere exchange, which are largely driven by meteorological variability, are found to play a particularly important role in driving ozone changes. The strong influence of emissions on NO2 and ozone interannual variability is largely confined to areas where intense biomass burning events occur. For CO, interannual variability is almost solely driven by emission changes, while for OH meteorology dominates, with the radiative influence of clouds being a very strong contributor. Through a simple attribution analysis for 1996–2000 we conclude that changing cloudiness drives 25% of the interannual variability of OH over Europe by affecting shortwave radiation. Over Indonesia this figure is as high as 71%. Changes in cloudiness contribute a small but non-negligible amount (up to 6%) to the interannual variability of ozone over Europe and Indonesia. This suggests that future assessments of trends in tropospheric oxidizing capacity should account for interannual variability in cloudiness, a factor neglected in many previous studies.

Warmer climate projections in CMIP6: the role of changes in the greenhouse gas concentrations from CMIP5 to CMIP6

2020 ◽  
Author(s):  
Klaus Wyser ◽  
Erik Kjellström ◽  
Torben Koenigk ◽  
Helena Martins ◽  
Ralf Döscher
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Impact ◽  
Earth Model ◽  
Minor Role ◽  
Climate Projections ◽  
First Results ◽  
Effective Radiative Forcing ◽  
A Minor ◽  
New Generation

<p>Many modelling groups have contributed with CMIP6 scenario experiments to the CMIP6 archive. The analysis of CMIP6 future projections has started and first results indicate that CMIP6 projections are warmer than their counterparts from CMIP5. To some extent this is explained with the higher climate sensitivity of many of the new generation of climate models. However, not only have models been updated since CMIP5 but also the forcings have changed from RCPs to SSPs. The new SSPs have been designed to have the same instantaneous radiative forcing at the end of the 21st century. However, we find that in the EC-Earth3 model the effective radiative forcing differs substantially when the GHG concentrations from the SSP are replaced by those from the corresponding RCP with the same nameplate RF. We estimate that for the SSP5-8.5 and SSP2-4.5 scenarios 50% or more of the stronger warming in CMIP6 than CMIP5 for the EC-Earth model can be explained by changes in GHG gas concentrations. Other changes in the forcing datasets such as aerosols only play a minor role for the additional warming. The discrepancy between RCP and SSP forcing datasets needs to be accounted for when comparing CMIP5 and CMIP6 climate projections and should be properly conveyed to the climate impact, adaptation and mitigation communities.</p>

Issues in the interpretation of climate model ensembles to inform decisions

2007 ◽  
Vol 365 (1857) ◽  
pp. 2163-2177 ◽  
Author(s):  
David A Stainforth ◽  
Thomas E Downing ◽  
Richard Washington ◽  
Ana Lopez ◽  
Mark New
Keyword(s):  
Climate Change ◽  
Climate Models ◽  
Climate Model ◽  
Global Scale ◽  
Climate Modelling ◽  
Large Ensembles ◽  
Recent Developments ◽  
Climate Model Simulations ◽  
Model Ensembles ◽  
A Minor

There is a scientific consensus regarding the reality of anthropogenic climate change. This has led to substantial efforts to reduce atmospheric greenhouse gas emissions and thereby mitigate the impacts of climate change on a global scale. Despite these efforts, we are committed to substantial further changes over at least the next few decades. Societies will therefore have to adapt to changes in climate. Both adaptation and mitigation require action on scales ranging from local to global, but adaptation could directly benefit from climate predictions on regional scales while mitigation could be driven solely by awareness of the global problem; regional projections being principally of motivational value. We discuss how recent developments of large ensembles of climate model simulations can be interpreted to provide information on these scales and to inform societal decisions. Adaptation is most relevant as an influence on decisions which exist irrespective of climate change, but which have consequences on decadal time-scales. Even in such situations, climate change is often only a minor influence; perhaps helping to restrict the choice of ‘no regrets’ strategies. Nevertheless, if climate models are to provide inputs to societal decisions, it is important to interpret them appropriately. We take climate ensembles exploring model uncertainty as potentially providing a lower bound on the maximum range of uncertainty and thus a non-discountable climate change envelope. An analysis pathway is presented, describing how this information may provide an input to decisions, sometimes via a number of other analysis procedures and thus a cascade of uncertainty. An initial screening is seen as a valuable component of this process, potentially avoiding unnecessary effort while guiding decision makers through issues of confidence and robustness in climate modelling information. Our focus is the usage of decadal to centennial time-scale climate change simulations as inputs to decision making, but we acknowledge that robust adaptation to the variability of present day climate encourages the development of less vulnerable systems as well as building critical experience in how to respond to climatic uncertainty.

scholarly journals The Rainfall Annual Cycle Bias over East Africa in CMIP5 Coupled Climate Models

2015 ◽  
Vol 28 (24) ◽  
pp. 9789-9802 ◽  
Author(s):  
Wenchang Yang ◽  
Richard Seager ◽  
Mark A. Cane ◽  
Bradfield Lyon
Keyword(s):  
East Africa ◽  
Annual Cycle ◽  
Climate Models ◽  
Western Indian Ocean ◽  
Shortwave Radiation ◽  
Coupled Models ◽  
Near Surface ◽  
Historical Simulation ◽  
Sst Bias ◽  
Short Rains

Abstract East Africa has two rainy seasons: the long rains [March–May (MAM)] and the short rains [October–December (OND)]. Most CMIP3/5 coupled models overestimate the short rains while underestimating the long rains. In this study, the East African rainfall bias is investigated by comparing the coupled historical simulations from CMIP5 to the corresponding SST-forced AMIP simulations. Much of the investigation is focused on the MRI-CGCM3 model, which successfully reproduces the observed rainfall annual cycle in East Africa in the AMIP experiment but its coupled historical simulation has a similar but stronger bias as the coupled multimodel mean. The historical–AMIP monthly climatology rainfall bias in East Africa can be explained by the bias in the convective instability (CI), which is dominated by the near-surface moisture static energy (MSE) and ultimately by the MSE’s moisture component. The near-surface MSE bias is modulated by the sea surface temperature (SST) over the western Indian Ocean. The warm SST bias in OND can be explained by both insufficient ocean dynamical cooling and latent flux, while the insufficient shortwave radiation and excess latent heat flux mainly contribute to the cool SST bias in MAM.

scholarly journals Investigation of the effective peak supersaturation for liquid-phase clouds at the high-alpine site Jungfraujoch, Switzerland (3580 m a.s.l.)

2014 ◽  
Vol 14 (2) ◽  
pp. 1123-1139 ◽  
Author(s):  
E. Hammer ◽  
N. Bukowiecki ◽  
M. Gysel ◽  
Z. Jurányi ◽  
C. R. Hoyle ◽  
...  
Keyword(s):  
Climate Models ◽  
Cloud Condensation Nuclei ◽  
Radiation Budget ◽  
Minor Role ◽  
Research Station ◽  
Cumulus Clouds ◽  
Air Masses ◽  
The Difference ◽  
Aerosol Cloud Interactions ◽  
A Minor

Abstract. Aerosols influence the Earth's radiation budget directly through absorption and scattering of solar radiation in the atmosphere but also indirectly by modifying the properties of clouds. However, climate models still suffer from large uncertainties as a result of insufficient understanding of aerosol-cloud interactions. At the high altitude research station Jungfraujoch (JFJ; 3580 m a.s.l., Switzerland) cloud condensation nuclei (CCN) number concentrations at eight different supersaturations (SS) from 0.24% to 1.18% were measured using a CCN counter during Summer 2011. Simultaneously, in-situ aerosol activation properties of the prevailing ambient clouds were investigated by measuring the total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems. Combining all experimental data, a new method was developed to retrieve the so-called effective peak supersaturation SSpeak, as a measure of the SS at which ambient clouds are formed. A 17-month CCN climatology was then used to retrieve the SSpeak values also for four earlier summer campaigns (2000, 2002, 2004 and 2010) where no direct CCN data were available. The SSpeak values varied between 0.01% and 2.0% during all campaigns. An overall median SSpeak of 0.35% and dry activation diameter of 87 nm was observed. It was found that the difference in topography between northwest and southeast plays an important role for the effective peak supersaturation in clouds formed in the vicinity of the JFJ, while differences in the number concentration of potential CCN only play a minor role. Results show that air masses coming from the southeast (with the slowly rising terrain of the Aletsch Glacier) generally experience lower SSpeak values than air masses coming from the northwest (steep slope). The observed overall median values were 0.41% and 0.22% for northwest and southeast wind conditions, respectively, corresponding to literature values for cumulus clouds and shallow-layer clouds. These cloud types are consistent with weather observations routinely performed at the JFJ.

scholarly journals The Effect of Water Vapor Originating from Land on the 2018 Drought Development in Europe

2021 ◽  
Author(s):  
Fares Al Hasan ◽  
Andreas Link ◽  
Ruud J. van der Ent
Keyword(s):  
Water Vapor ◽  
Land Surface ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Relative Increase ◽  
Minor Role ◽  
Summer Drought ◽  
Southeast Europe ◽  
Time And Space ◽  
A Minor

The 2018 summer drought in Europe was particularly extreme in terms of intensity and impact due to the combination of low rainfall and high temperatures. However, it remains unclear how this drought developed in time and space in such an extreme way. In this study we aimed to get a better understanding of the role of land-atmosphere interactions. More specifically, we investigated whether there was a change in water vapor originating from land, if that caused a reduction in rainfall, and by this mechanism possibly the propagation and intensification of the drought in Europe. Our first step was to use remote sensing products for soil moisture content (SMC) and the normalized difference vegetation index (NDVI) to see where the 2018 drought started and how it developed in time and space. Our SMC and NDVI analysis showed that the 2018 drought started to impact the soil and vegetation state in June in Scandinavia and the British Isles. After that it moved towards the West of Europe where it intensified in July and August. In September, it started to decay. In October, drought was observed in southeast Europe as well. Based on the observed patterns we divided Europe into six regions of similar spatiotemporal characteristics of SMC and NDVI. Then, we used a global gridded dataset of the fate of land evaporation (i.e., where it ends up as precipitation) to investigate whether the drought intensification and propagation was impacted by the reduction in water vapor transported from the regions that first experienced the drought. This impact was investigated by identifying the anomalies in the water vapor originating from land recycling, imports and exports within Europe during the spring, summer, and autumn seasons. From these regions we identified four drought regions and investigated the changes in water vapor originating from source regions on the development of drought in those regions. It was found that during the onset phase of the 2018 drought in Europe that the water vapor originating from land played an important role in mitigating the precipitation anomalies as, for example, the share of land evaporation contributing to precipitation increased from 27% (normal years) to 38% (2018) during July in West of Europe. Land evaporation played a minor role in amplifying it during the intensification phase of the drought as the share of land evaporation contribution to precipitation decreased from 23% (normal years) to 21% (2018) during August in West of Europe. These findings are somewhat in contrast to similar studies in other continents that found the land surface to play a strong amplifying role for drought development. Subsequently, we found that the relative increase in the amount of land water vapor originating from eastern half of Europe played a role in delaying the onset and accelerating the decay of the 2018 drought in West of Europe.

scholarly journals Investigation of the effective peak supersaturation for liquid-phase clouds at the high-alpine site Jungfraujoch, Switzerland (3580 m a.s.l.)

2013 ◽  
Vol 13 (8) ◽  
pp. 20419-20462 ◽  
Author(s):  
E. Hammer ◽  
N. Bukowiecki ◽  
M. Gysel ◽  
Z. Jurányi ◽  
C. R. Hoyle ◽  
...  
Keyword(s):  
Climate Models ◽  
Cloud Condensation Nuclei ◽  
Radiation Budget ◽  
Minor Role ◽  
Research Station ◽  
Cumulus Clouds ◽  
Air Masses ◽  
The Difference ◽  
Aerosol Cloud Interactions ◽  
A Minor

Abstract. Aerosols influence the Earth's radiation budget directly through absorption and scattering of solar radiation in the atmosphere but also indirectly by modifying the properties of clouds. However, climate models still suffer from large uncertainties as a result of insufficient understanding of aerosol-cloud interactions. At the high altitude research station Jungfraujoch (JFJ; 3580 m a.s.l., Switzerland) cloud condensation nuclei (CCN) number concentrations at eight different supersaturations (SS) from 0.24% to 1.18% were measured using a CCN counter during Summer 2011. Simultaneously, in-situ aerosol activation properties of the prevailing ambient clouds were investigated by measuring the total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems. Combining all experimental data, a new method was developed to retrieve the so-called effective peak supersaturation SSpeak, as a measure of the SS at which ambient clouds are formed. A 17 month CCN climatology was then used to retrieve the SSpeak values also for four earlier summer campaigns (2000, 2002, 2004 and 2010) where no direct CCN data were available. The SSpeak values varied between 0.01% and 2.0% during all campaigns. An overall median SSpeak of 0.35% and dry activation diameter of 87 nm was observed. It was found that the difference in topography between northwest and southeast plays an important role for the effective peak supersaturation in clouds formed in the vicinity of the JFJ, while differences in the number concentration of potential CCN only play a minor role. Results show that air masses coming from the southeast (with the slowly rising terrain of the Aletsch Glacier) generally experience lower SSpeak values than air masses coming from the northwest (steep slope). The observed overall median values were 0.41% and 0.22% for northwest and southeast wind conditions, respectively, corresponding to literature values for cumulus clouds and shallow-layer clouds. These cloud types are consistent with weather observations routinely performed at the JFJ.

scholarly journals Hurricane annual cycle controlled by both seeds and genesis probability

2021 ◽  
Vol 118 (41) ◽  
pp. e2108397118
Author(s):  
Wenchang Yang ◽  
Tsung-Lin Hsieh ◽  
Gabriel A. Vecchi
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
Annual Cycle ◽  
Climate Models ◽  
Essential Elements ◽  
Abrupt Increase ◽  
Annual Cycles ◽  
The North ◽  
Concise Representation ◽  
The North Atlantic

Understanding tropical cyclone (TC) climatology is a problem of profound societal significance and deep scientific interest. The annual cycle is the biggest radiatively forced signal in TC variability, presenting a key test of our understanding and modeling of TC activity. TCs over the North Atlantic (NA) basin, which are usually called hurricanes, have a sharp peak in the annual cycle, with more than half concentrated in only 3 mo (August to October), yet existing theories of TC genesis often predict a much smoother cycle. Here we apply a framework originally developed to study TC response to climate change in which TC genesis is determined by both the number of pre-TC synoptic disturbances (TC “seeds”) and the probability of TC genesis from the seeds. The combination of seeds and probability predicts a more consistent hurricane annual cycle, reproducing the compact season, as well as the abrupt increase from July to August in the NA across observations and climate models. The seeds-probability TC genesis framework also successfully captures TC annual cycles in different basins. The concise representation of the climate sensitivity of TCs from the annual cycle to climate change indicates that the framework captures the essential elements of the TC climate connection.

scholarly journals A module to convert spectral to narrowband snow albedo for use in climate models: SNOWBAL v1.2

2019 ◽  
Vol 12 (12) ◽  
pp. 5157-5175 ◽  
Author(s):  
Christiaan T. van Dalum ◽  
Willem Jan van de Berg ◽  
Quentin Libois ◽  
Ghislain Picard ◽  
Michiel R. van den Broeke
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Greenland Ice Sheet ◽  
Shortwave Radiation ◽  
Transfer Model ◽  
Snow Albedo ◽  
Radiation Scheme

Abstract. Snow albedo schemes in regional climate models often lack a sophisticated radiation penetration scheme and generally compute only a broadband albedo. Here, we present the Spectral-to-NarrOWBand ALbedo module (SNOWBAL, version 1.2) to couple effectively a spectral albedo model with a narrowband radiation scheme. Specifically, the Two-streAm Radiative TransfEr in Snow model (TARTES) is coupled with the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), cycle 33R1, atmospheric radiation scheme based on the Rapid Radiation Transfer Model, which is embedded in the Regional Atmospheric Climate Model version 2.3p2 (RACMO2). This coupling allows to explicitly account for the effect of clouds, water vapor, snow impurities and snow metamorphism on albedo. Firstly, we present a narrowband albedo method to project the spectral albedos of TARTES onto the 14 spectral bands of the IFS shortwave radiation scheme using a representative wavelength (RW) for each band. Using TARTES and spectral downwelling surface irradiance derived with the DIScrete Ordinate Radiative Transfer atmospheric model, we show that RWs primarily depend on the solar zenith angle (SZA), cloud content and water vapor. Secondly, we compare the TARTES narrowband albedo, using offline RACMO2 results for south Greenland, with the broadband albedo parameterizations of Gardner and Sharp (2010), currently implemented in RACMO2, and the multi-layered parameterization of Kuipers Munneke et al. (2011, PKM). The actual absence of radiation penetration in RACMO2 leads on average to a higher albedo compared with TARTES narrowband albedo. Furthermore, large differences between the TARTES narrowband albedo and PKM and RACMO2 are observed for high SZA and clear-sky conditions, and after melt events when the snowpack is very inhomogeneous. This highlights the importance of accounting for spectral albedo and radiation penetration to simulate the energy budget of the Greenland ice sheet.

Climate Change and Human Conflict in the Sahel

2021 ◽  
pp. 268-284
Author(s):  
Tor A. Benjaminsen
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Climate Models ◽  
State Policies ◽  
Resource Scarcity ◽  
Minor Role ◽  
Armed Groups ◽  
Entire Region ◽  
Human Conflict ◽  
A Minor

Most climate models predict more rain in the future in the Sahel, but with more concentrated rainfall. Since the droughts of the 1980s, rains have increased, which has led to a regreening of the entire region. There is, however, a dominant narrative postulating that climate change will lead to drier conditions and desertification in the Sahel, which again will lead to resource scarcity, widespread migration, and more conflicts. This chapter critically investigates this narrative based on a review of international research. It considers conflict between farmers and herders, between the state and armed groups, in addition to jihadi violence that has increased in region in recent years. It concludes that the droughts in the 1980s only played a minor role in explaining conflicts, while the root causes were political and historical. State policies tend to lead to the marginalization of pastoralists. In areas where pastoralism and farming overlap as the main forms of land use, there are continuous conflicts of varying scale and intensity. These conflicts are primarily caused by politics, not climate change.

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