Mindlin Julia, Shepherd Theodore G, Vera Carolina S, Osman Marisol, Zappa Giuseppe, Lee Robert W, Hodges Kevin I
Centro de Investigaciones del Mar y la Atmósfera, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de Buenos Aires, Buenos Aires, Argentina.
Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
Clim Dyn. 2020;54(9):4399-4421. doi: 10.1007/s00382-020-05234-1. Epub 2020 May 6.
As evidence of climate change strengthens, knowledge of its regional implications becomes an urgent need for decision making. Current understanding of regional precipitation changes is substantially limited by our understanding of the atmospheric circulation response to climate change, which to a high degree remains uncertain. This uncertainty is reflected in the wide spread in atmospheric circulation changes projected in multimodel ensembles, which cannot be directly interpreted in a probabilistic sense. The uncertainty can instead be represented by studying a discrete set of physically plausible storylines of atmospheric circulation changes. By mining CMIP5 model output, here we take this broader perspective and develop storylines for Southern Hemisphere (SH) midlatitude circulation changes, conditioned on the degree of global-mean warming, based on the climate responses of two remote drivers: the enhanced warming of the tropical upper troposphere and the strengthening of the stratospheric polar vortex. For the three continental domains in the SH, we analyse the precipitation changes under each storyline. To allow comparison with previous studies, we also link both circulation and precipitation changes with those of the Southern Annular Mode. Our results show that the response to tropical warming leads to a strengthening of the midlatitude westerly winds, whilst the response to a delayed breakdown (for DJF) or strengthening (for JJA) of the stratospheric vortex leads to a poleward shift of the westerly winds and the storm tracks. However, the circulation response is not zonally symmetric and the regional precipitation storylines for South America, South Africa, South of Australia and New Zealand exhibit quite specific dependencies on the two remote drivers, which are not well represented by changes in the Southern Annular Mode.
随着气候变化证据的增强，了解其区域影响成为决策的迫切需求。目前对区域降水变化的理解在很大程度上受到我们对大气环流对气候变化响应的理解的限制，而这在很大程度上仍然不确定。这种不确定性反映在多模式集合中预测的大气环流变化的广泛差异上，这些差异无法直接从概率意义上进行解释。相反，这种不确定性可以通过研究一组离散的大气环流变化的物理上合理的情景来表示。通过挖掘CMIP5模型输出，我们从更广泛的角度出发，基于两个远程驱动因素的气候响应，即热带对流层上层变暖加剧和平流层极涡加强，针对全球平均变暖程度，制定了南半球（SH）中纬度环流变化的情景。对于南半球的三个大陆区域，我们分析了每个情景下的降水变化。为了便于与以前的研究进行比较，我们还将环流和降水变化与南半球环状模的变化联系起来。我们的结果表明，对热带变暖的响应导致中纬度西风增强，而对平流层涡旋延迟崩溃（对于12月至次年2月）或加强（对于6月至8月）的响应导致西风带和风暴路径向极移动。然而，环流响应不是纬向对称的，南美洲、南非、澳大利亚南部和新西兰的区域降水情景对这两个远程驱动因素表现出相当特殊的依赖性，而南半球环状模的变化并不能很好地体现这些依赖性。
