The semi-arid African Sahel region is highly sensitive to changes in monsoon precipitation, as much of the region’s workforce is employed in the agricultural industry (Hamro-Drotz and Programme 2011). Thus, studying the response of rainfall and aridity in this region to radiative perturbations is a matter of pressing humanitarian relevance. In addition, there is evidence to suggest that spatially asymmetric volcanic aerosols produce different hydroclimatic responses based on their hemispheric symmetry, both globally and in the Sahel. We use two different climate models, GFDL’s FLOR model (Vecchi et al. in J Clim 27(21):7994–8016, 2014) and NCAR’s CESM 1.1 model (Otto-Bliesner et al. in Bull Am Meteorol Soc 97(5):735–754, 2016), to characterize the response of rainfall in the Sahel to large volcanic eruptions based on the meridional symmetry of the volcanic eruptions. We find that in both the FLOR experiments simulating three large twentieth century eruptions and in the CESM Last Millennium Ensemble simulations of 46 historic volcanic eruptions, asymmetric Northern Hemisphere cooling causes a subsequent drying response in the Sahel, and Southern Hemisphere cooling causes a wetting, or “greening” response. Symmetric volcanic eruptions have a relatively small effect on rainfall in the Sahel. We also find that the FLOR results show a consistent response in the annual rainfall cycle in the Sahel for all three of the eruptions analyzed, with a reduction in rainfall in early summer followed by an increased rainfall in late summer. The annual cycle response of rainfall in the Sahel from the CESM experiments is different, in that the SH eruptions cause a rainfall maximum in August, NH eruptions cause a rainfall minimum in September, and symmetric eruptions show a slight increase in August and a decrease in October. Our results highlight the need for accurate meridional structures in historic volcanic forcing data used for climate models as well as the need for further study on regional effects of hemispherically asymmetric radiative forcing, especially as they might pertain to aerosol geoengineering.

半干旱的非洲萨赫勒地区对季风降水变化高度敏感，因为该地区的大部分劳动力都从事农业生产（Hamro-Drotz and Programme 2011）。因此，研究该地区的降雨和干旱对辐射扰动的响应是紧迫的人道主义问题。此外，有证据表明，空间不对称的火山气溶胶基于其半球对称性在全球和萨赫勒地区产生不同的水文气候响应。我们使用两种不同的气候模型，即GFDL的FLOR模型（Vecchi等，J Clim 27（21）：7994-8016，2014）和NCAR的CESM 1.1模型（Otto-Bliesner等，Bull Am Meteorol Soc 97（5））。 ：735–754，2016年），根据火山喷发的子午对称性来表征萨赫勒地区降雨对大型火山喷发的响应。我们发现，在模拟三个20世纪大型喷发的FLOR实验以及在46个历史性火山喷发的CESM上一千年合奏模拟中，北半球的不对称冷却都会导致随后的萨赫勒地区干燥反应，而南半球的冷却则会导致湿润现象，或者“绿化”反应。对称的火山喷发对萨赫勒地区的降雨影响相对较小。我们还发现，FLOR结果显示，在萨赫勒地区分析的所有三个喷发中，年度降水周期的响应都是一致的，夏初的降雨量减少，夏末的降雨量增加。来自CESM实验的萨赫勒地区降雨的年循环响应有所不同，因为SH喷发导致8月降雨量最大，NH喷发导致9月降雨量最小，而对称喷发则8月略有增加，而P减少。十月。我们的结果强调，在用于气候模型的历史火山强迫数据中需要精确的子午线结构，并且需要进一步研究半球形非对称辐射强迫的区域效应，尤其是因为它们可能与气溶胶地球工程有关。