AR：2021/22冬季华南降水偏多的可能原因

冬季降水常伴低温出现，会给交通能、源供应、人民生活等带来不利影响。2021年是“双拉尼娜年”。一般拉尼娜年华南降水偏少，但2021/2022年冬季中国华南降水偏多，为1961年以来同期最多的一年（图1）。该论文研究分析了2021/2022冬季华南降水异常偏多的可能原因。结果表明： 2021/2022年冬季，青藏高原为异常垂直上升运动，对华南降水偏多有直接的影响；线性因果信息流分析表明前期热带大西洋对冬季青藏高原异常垂直运动有显著的信息流，尤其在前期秋季；进一步研究发现热带大西洋异常可以引起波列，导致冬季青藏高原上垂直环流的异常（图2）；2021/2022年从前期秋季到冬季在热带大西洋上维持显著的异常，其引起的波列异常导致了青藏高原的环流异常，从而引起华南降水偏多（图3）。

Fig.1 DJF rainfall percentage anomalies over China. (a) 2021/2022;(b) Composite anomalies during DJF of La Niña events. (c) Composite difference between the typical events defined by the vertical velocity index over TP. The shaded areas represent t-test values exceeding the 95 % confidence level in (b) and (c).

Fig.2 Normalized anomalies of the DJF circulation fields. (a) the composite differences of DJF stream function at 500hPa between the typical years defined by ATI (the interval of the contours is 0.5). (b) the normalized anomalies of DJF stream function of 2021/2022. (c) the composite differences of DJF stream function (shaded areas with significant level exceeding 0.05 shown) and winds (red arrows with those statistically significant over the level of 0.05 shown) at 500hPa, the normalized stream function (contours with values of -2, -1,0,1,2 drawn) and winds (arrows) of 2021/2022 DJF. Here ‘C’ and ‘A’ in the (c) means anomaly ‘Cyclone’ and ‘Anticyclone’, respectively.

Fig.3The anomalies of the stream function (contours, Units: m2/s) and the horizontal wave flux (arrows, Units: m2/s2) at 250hPa.

相关成果已在《Atmospheric Research》期刊上发表。