Differences in spring precipitation over southern China associated with multiyear La Ni?a events

Composite analyses were performed in this study to reveal the difference in spring precipitation over southern China during multiyear La Ni?a events during 1901 to 2015. It was found that there is significantly below-normal precipitation during the first boreal spring, but above-normal precipitation during the second year. The difference in spring precipitation over southern China is correlative to the variation in western North Pacific anomalous cyclone(WNPC), which can in turn be attributed to the different sea surface temperature anomaly(SSTA) over the Tropical Pacific. The remote forcing of negative SSTA in the equatorial central and eastern Pacific and the local air-sea interaction in the western North Pacific are the usual causes of WNPC formation and maintenance.SSTA in the first spring is stronger than those in the second spring. As a result, the intensity of WNPC in the first year is stronger, which is more likely to reduce the moisture in southern China by changing the moisture transport, leading to prolonged precipitation deficits over southern China. However, the tropical SSTA signals in the second year are too weak to induce the formation and maintenance of WNPC and the below-normal precipitation over southern China. Thus, the variation in tropical SSTA signals between two consecutive springs during multiyear La Ni?a events leads to obvious differences in the spatial pattern of precipitation anomaly in southern China by causing the different WNPC response.

2022年汛期气候预测效果评述及先兆信号分析

2022年汛期,国家气候中心准确预测了“全国气候年景总体偏差,区域性、阶段性旱涝灾害明显,降水空间差异显著,主要多雨区在我国北方”的总趋势,较好、较早把握了汛期主雨带位置和全国旱涝分布。对东亚夏季风和雨季季节进程“南海夏季风5月第3候爆发,长江中下游入梅偏早,梅雨量偏少,以及华北雨季开始偏早,雨量偏多”的预测与实况一致。对夏季台风生成个数较常年偏少,盛夏出现北上台风可能性大的预测与实况基本吻合。准确预测了全国平均气温趋势和高温异常特征。对“夏季我国中东部大部气温偏高,华东、华中、新疆等地高温日数较常年同期偏多,可能出现阶段性高温热浪”的预测与实况一致。主要不足之处是对长江中下游和川渝地区高温干旱的范围和极端程度估计不足。2022年汛期预测重点考虑连续La Ni a事件和印度洋偶极子负位相对东亚夏季风环流的影响,夏季西太平洋副热带高压强度偏强,脊线位置偏北,东亚夏季风偏强,初夏东北冷涡活跃,导致汛期主雨带位于东北、华北和西北地区东部等地。