近60年华北夏季降水异常的动力水汽条件分析

Analysis of the Dynamics and Water Vapor Conditions of SummerPrecipitation Anomalies in North China in Recent 60 Years

摘要:

为认识华北夏季降水异常的成因和改进气候监测预测技术,本文利用1961—2021年华北夏季降水资料、美国环境预测中心和大气研究中心(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)再分析资料,采用相关、合成和环流异常重构等方法,分析了华北夏季(6—8月)降水异常的环流背景以及东亚副热带夏季风、华北动力上升指数变化与华北夏季降水的关系。结果表明：(1)华北夏季降水异常偏多的环流条件是,夏季500hPa乌拉尔山高压脊偏强、贝加尔湖槽偏深、西北太平洋副高偏北偏西位于朝鲜半岛附近,华北处于“东高西低”的环流形势下,动力上升条件有利；与此同时,850hPa印度季风偏强、东亚副热带夏季风显著偏强,华北水汽来源充足。(2)本文定义的东亚副热带夏季风指数和华北动力上升指数对华北夏季降水异常有很好的指示意义。当两个指数都偏强时,华北夏季降水异常偏多；如果两个指数都偏弱,则华北夏季降水异常偏少；如果两个指数强弱不一致时,华北夏季降水基本为正常。(3)华北夏季降水异常偏多或偏少是东亚副热带夏季风和华北动力上升运动协同作用的结果。东亚副热带夏季风偏强(华北动力上升运动偏强)年,500hPa层贝加尔湖槽加深、西北太平洋副热带高压偏北偏西,华北处于“东高西低”的环流控制下,动力上升条件有力；同时,850hPa层印度夏季风、东亚副热带夏季风偏强,造成热带印度洋西风水汽输送以及东亚副热带地区偏南风水汽输送会加强,华北水汽来源充足。以上这种情况会造成华北夏季降水异常偏多。反之,华北夏季降水会异常偏少。(4)前期4-5月,500hPa层贝加尔湖槽加深、西北太平洋副热带高压偏北,850hPa层东亚地区偏南风显著偏强,这些可以作为华北夏季降水异常偏多的一个气候监测预测指标。

Abstract:

In order to understand the causes of summer precipitation anomalies in North China and improve climate monitoring and prediction technology, based on the summer precipitation data in North China and NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data from 1961 to 2021, using the methods of correlation, synthesis and circulation anomaly reconstruction, the circulation background of summer (June -August) precipitation anomaly in North China and the relationship between East Asian subtropical summer monsoon, North China dynamic rise index and summer precipitation in North China are analyzed. The results show that: (1) the circulation conditions of abnormal precipitation in North China in summer are that the high ridge of Ural Mountain at 500hPa in summer is stronger, the Baikal Lake trough is deeper, the subtropical high in the Northwest Pacific is north by west near the Korean Peninsula, and North China is in the circulation situation of "high in the East and low in the west", so the dynamic rising conditions are favorable. At the same time, the 850hPa Indian monsoon is stronger, the East Asian subtropical summer monsoon is significantly stronger, and the water vapor source in North China is sufficient. (2) The East Asian subtropical summer monsoon index and North China dynamic rise index defined in this paper have a good indication of summer precipitation anomalies in North China. When the two indexes are stronger, the summer precipitation in North China is abnormally more. If both indexes are weak, the summer precipitation in North China is abnormally less. If the two indexes are inconsistent, the summer precipitation in North China is basically normal. (3) The abnormally more or less summer rainfall in North China is the result of the synergy of the East Asian subtropical summer monsoon and the dynamic upward movement in North China. The subtropical summer monsoon in East Asia is stronger (the dynamic upward movement in North China is stronger), the Baikal trough in the 500hPa layer is deepened, the subtropical high in the Northwest Pacific is north by west, and North China is under the control of the circulation of "high in the East and low in the West", so the dynamic upward conditions are favorable. At the same time, the Indian summer monsoon at 850hPa and the subtropical summer monsoon in East Asia are relatively strong, which will strengthen the water vapor transmission of the west wind in the tropical Indian Ocean and the south wind in the subtropical region of East Asia, and the water vapor source in North China is sufficient. The above situation will cause abnormally more summer precipitation in North China. On the contrary, the summer precipitation in North China will be abnormally less. (4) From April to May in the early stage, the Baikal trough in the 500hPa layer deepened, the subtropical high in the Northwest Pacific was northerly, and the southerly wind in East Asia in the 850hPa layer was significantly stronger, which can be used as a climate monitoring and prediction index for the abnormally more summer precipitation in North China.