Mid‐Holocene Sahara‐Sahel Precipitation From the Vantage of Present‐Day Climate

2020 ◽  
Vol 47 (16) ◽  
Author(s):  
Peter Molnar ◽  
Balaji Rajagopalan
Keyword(s):  
Sahel Precipitation

scholarly journals Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

2007 ◽  
Vol 20 (8) ◽  
pp. 1445-1467 ◽  
Author(s):  
Masaru Yoshioka ◽  
Natalie M. Mahowald ◽  
Andrew J. Conley ◽  
William D. Collins ◽  
David W. Fillmore ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Africa ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Desert Dust ◽  
Direct Radiative Forcing ◽  
Sahel Region ◽  
Precipitation Reduction ◽  
Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

scholarly journals Surface Albedo Response to Sahel Precipitation Changes

Eos ◽  
2007 ◽  
Vol 88 (3) ◽  
pp. 25 ◽  
Author(s):  
Yves Govaerts ◽  
Alessio Lattanzio
Keyword(s):  
Surface Albedo ◽  
Precipitation Changes ◽  
Sahel Precipitation

Forced modulations of Sahel rainfall at decadal timescale over the 20th Century.

2021 ◽  
Author(s):  
Cassien Diabe Ndiaye ◽  
Juliette Mignot ◽  
Elsa Mohino
Keyword(s):  
North Atlantic Ocean ◽  
Coupled Model ◽  
Internal Variability ◽  
Boreal Summer ◽  
Semiarid Region ◽  
Rainfall Regime ◽  
Anthropogenic Aerosols ◽  
Coupled Models ◽  
External Forcings ◽  
Sahel Precipitation

<p>The semiarid region of the Sahel was marked during the 20<sup>th</sup> Century by significant modulations of its rainfall regime. Part of these modulations has been associated with the internal variability of the climate system, mediated by changes in oceanic sea surface temperature (SST). We show here that the external forcings, and in particular anthropogenic aerosols, might have played a role more important than previously thought in setting these variations. The study is based on the recent simulations performed for CMIP6 with the IPSL-CM6A-LR coupled model. As in most coupled models, the maximum precipitation is limited to the southern Sahel during boreal summer in the IPSL-CM6A-LR model. A novel definition of the Sahel precipitation region is proposed in order to take this bias into account. Our results show that external forcings induce decadal modulations of Sahel precipitation that correlate significantly at 0.6 with the observed precipitations and that the anthropogenic aerosols explain more than 70% of these modulations. These results confirm recent results of CMIP6 highlighting an important role of aerosol forcing for the decadal climate in and around the North Atlantic ocean.</p>

scholarly journals Correction to: Model uncertainties in climate change impacts on Sahel precipitation in ensembles of CMIP5 and CMIP6 simulations

2020 ◽  
Vol 55 (7-8) ◽  
pp. 2309-2310
Author(s):  
Paul-Arthur Monerie ◽  
Caroline M. Wainwright ◽  
Moussa Sidibe ◽  
Akintomide Afolayan Akinsanola
Keyword(s):  
Climate Change ◽  
Climate Change Impacts ◽  
Model Uncertainties ◽  
Sahel Precipitation

Anthropogenic Aerosols Dominate Forced Multidecadal Sahel Precipitation Change through Distinct Atmospheric and Oceanic Drivers

2020 ◽  
Vol 33 (23) ◽  
pp. 10187-10204
Author(s):  
Haruki Hirasawa ◽  
Paul J. Kushner ◽  
Michael Sigmond ◽  
John Fyfe ◽  
Clara Deser
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Forced Response ◽  
Sea Surface ◽  
Atmospheric Response ◽  
Anthropogenic Aerosols ◽  
Coupled General Circulation Model ◽  
Large Ensembles ◽  
Primary Driver ◽  
Sahel Precipitation

AbstractSahel precipitation has undergone substantial multidecadal time scale changes during the twentieth century that have had severe impacts on the region’s population. Using initial-condition large ensembles (LE) of coupled general circulation model (GCM) simulations from two institutions, forced multidecadal variability is found in which Sahel precipitation declines from the 1950s to 1970s and then recovers from the 1970s to 2000s. This forced variability has similar timing to, but considerably smaller magnitude than, observed Sahel precipitation variability. Isolating the response using single forcing simulations within the LEs reveals that anthropogenic aerosols (AA) are the primary driver of this forced variability. The roles of the direct-atmospheric and the ocean-mediated atmospheric responses to AA forcing are determined with the atmosphere–land GCM (AGCM) components of the LE coupled GCMs. The direct-atmospheric response arises from changes to aerosol and precursor emissions with unchanged oceanic boundary conditions while the ocean-mediated response arises from changes to AA-forced sea surface temperatures and sea ice concentrations diagnosed from the AA-forced LE. In the AGCMs studied here, the direct-atmospheric response dominates the AA-forced 1970s − 1950s Sahel drying. On the other hand, the 2000s − 1970s wetting is mainly driven by the ocean-mediated effect, with some direct atmospheric contribution. Although the responses show differences, there is qualitative agreement between the AGCMs regarding the roles of the direct-atmospheric and ocean-mediated responses. Since these effects often compete and show nonlinearity, the model dependence of these effects and their role in the net aerosol-forced response of Sahel precipitation need to be carefully accounted for in future model analysis.

The effect of dust absorption on Sahel precipitation

2020 ◽  
Author(s):  
Yves Balkanski
Keyword(s):  
Iron Oxide ◽  
Water Budget ◽  
Summer Precipitation ◽  
Shortwave Radiation ◽  
Dust Particles ◽  
Oxide Content ◽  
Liquid Water Path ◽  
Aerosol Absorption ◽  
Dust Absorption ◽  
Sahel Precipitation

<p>Absorption of shortwave radiation by dust depends on its iron oxide content. Iron oxides amount to just a few percents of dust mineralogy. In the Sahel, the amount of iron oxide in soils is significantly greater than over the rest of North Africa. Recent measurements from the AER-D campaign have evidenced the presence of large dust particles over Northern African sources, which measurements showed absorb higher shortwave radiation than smaller ones.</p><p>I present two 100-years simulations of the earth system model IPSLCM6, one with a detailed description of dust and one without dust. Over the summer months (JJAS), dust absorption amounts to 25 W.m<sup>-2</sup> over the region. The changes caused by this absorption to the water budget are analyzed. Dust absorption causes an increase of 16% of summer Western Sahel precipitation, whereas in the Eastern Sahel, summer precipitation is increased by 7%. The analysis is extended to evaporation, surface relative humidity, low-level clouds and total cloud liquid water path, all of which show a significant increase caused by absorbing dust.</p><p>The water budget over the Sahel is computed over an airshed that covers the region, 16W:36E and 10N:20N from the surface to 200mb, contrasting the water flux with and without aerosol absorption. Dust absorption causes a change in the mean circulation between 1000 and 800mb that induces an increased inflow of moist air at these levels at the western and southern Sahel boundaries during the summer monsoon.  Hence, it is important to understand the influence of aerosol absorption when studying the causes of variations in Sahel precipitation.</p>

scholarly journals The Effects of Anthropogenic and Volcanic Aerosols and Greenhouse Gases on 20th Century Sahel Precipitation

2020 ◽  
Author(s):  
Rebecca Herman ◽  
Michela Biasutti ◽  
Alessandra Giannini ◽  
Yochanan Kushnir
Keyword(s):  
Greenhouse Gases ◽  
20Th Century ◽  
Volcanic Aerosols ◽  
Sahel Precipitation
Sign in / Sign up

Export Citation Format

Share Document