The effect of explicit convection on climate change in the West African monsoon and central West African Sahel rainfall
The effect of explicit convection on climate change in the West African monsoon and central West African Sahel rainfall
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DOI：
10.1175/jcli-d-21-0258.1
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发表时间：
2021-12
影响因子：
4.9
通讯作者：
L. A. S. J. Ackson;J. O. H. M. Arsham;D. O. J. P. Arker;D. E. L. F. Inney;R. O. G. J. F. Itzpatrick;D. A. P. R. Owell;R. A. A. S. Tratton-R.-A.-A.-S.-Tratton-2302176934;S. I. T. Ucker
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文献类型：
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作者：
L. A. S. J. Ackson;J. O. H. M. Arsham;D. O. J. P. Arker;D. E. L. F. Inney;R. O. G. J. F. Itzpatrick;D. A. P. R. Owell;R. A. A. S. Tratton-R.-A.-A.-S.-Tratton-2302176934;S. I. T. Ucker
西非季风（WAM）是西非气候的主要特征，提供了年降雨量的大部分。对西非萨赫勒地区未来降雨量的预测非常不确定，一个关键原因可能是潮湿对流，这通常是全球气候模型中的参数。在这里，我们使用泛非洲对流允许模拟（CP 4），以及参数化对流模拟（P25），以确定支持显式对流对西非萨赫勒中部（8°W-2°E，12-17°N）气候变化影响的关键过程。在当前气候条件下，CP 4与P25相比，在多个尺度上影响WAM过程。降水、水汽辐合和大气湿度的日变化存在差异。有高档的影响：WAM向北深入，萨赫勒北部和撒哈拉热低区湿度较大，撒哈拉地区副热带下沉速率较弱，热带雨带内上升较深。在气候变化的影响下，西北风向北移动，Hadley环流在P25和CP 4减弱。然而，P25和CP 4之间的差异仍然存在，这是由日尺度和大尺度的过程差异所支撑的。CP 4的平均降雨量增加了17.1%，而P25的平均降雨量增加了6.7%，并且CP 4的热带上升和副热带下沉都有更大的减弱。这些发现显示了参数化对流的局限性，并展示了显式对流模拟可以为气候建模者和气候政策决策者提供的价值。
The West African monsoon (WAM) is the dominant feature of West African climate providing the majority of annual rainfall. Projections of future rainfall over the West African Sahel are deeply uncertain with a key reason likely to be moist convection, which is typically parameterized in global climate models. Here, we use a pan-Africa convection permitting simulation (CP4), alongside a parameterized convection simulation (P25), to determine the key processes that underpin the effect of explicit convection on the climate change of the central West African Sahel (8°W-2°E, 12-17°N). In current climate, CP4 affects WAM processes on multiple scales compared to P25. There are differences in the diurnal cycles of rainfall, moisture convergence, and atmospheric humidity. There are upscale impacts: the WAM penetrates farther north, there is greater humidity over the north Sahel and the Saharan heat low regions, the sub-tropical subsidence rate over the Sahara is weaker, and ascent within the tropical rain belt is deeper. Under climate change, the WAM shifts northwards and Hadley circulation weakens in P25 and CP4. The differences between P25 and CP4 persist, however, underpinned by process differences at the diurnal and large-scales. Mean rainfall increases 17.1% in CP4 compared to 6.7% in P25 and there is greater weakening in tropical ascent and sub-tropical subsidence in CP4. These findings show the limitations of parameterized convection and demonstrate the value that explicit convection simulations can provide to climate modellers and climate policy decision makers.