华北近60年夏季降水年际异常与大气动力、水汽条件关系的研究

A study on the relationship between interannual summer precipitation anomalies in North China and atmospheric dynamics and water vapor conditions in the recent 60 years

本文基于华北夏季降水数据、NCEP/NCAR再分析环流数据,采用了相关、合成和环流异常回归重构等方法,分析了东亚副热带夏季风指数、华北大气动力上升指数与华北夏季降水的关系。主要结果如下:1)东亚副热带夏季风指数、华北大气动力上升指数与华北夏季降水有很好的对应关系。当两个指数偏强时,华北夏季降水会异常偏多;两个指数偏弱,华北夏季降水异常偏少;如果两个指数强弱不一致时,华北会出现区域性降水偏多情况,但全区整体降水量基本为正常值。2)华北夏季降水异常是东亚副热带夏季风和华北大气动力上升运动协同作用的结果。在东亚副热带夏季风指数、华北大气动力上升指数偏强年,夏季500 hPa层贝加尔湖槽会加深、西北太平洋副热带高压会偏北,华北处于“东高西低”的环流型控制下,西部低槽东移受阻,在华北维持较长时间的大气上升运动;850 hPa层印度夏季风、东亚副热带夏季风会偏强,这时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或东南风水汽输送会加强,华北水汽来源充足。这种高、低空环流配置非常有利于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。3)前期4—5月,东亚副热带夏季风指数、华北大气动力上升指数偏强,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。

To enhance our understanding of the causes behind interannual summer precipitation anomalies in North China and improve climate monitoring and prediction technologies,this study examines the relationship between the East Asian subtropical summer monsoon index(EAMI),the North China atmospheric dynamic rise index(HBDRI),and the summer precipitation in North China.Correlation analysis,synthesis,and circulation anomaly regression reconstruction methods are employed using summer precipitation data in North China and NCEP/NCAR reanalysis circulation data.The main findings are as follows:1)The EAMI and HBDRI exhibit a significant correspondence with summer precipitation in North China.Stronger values of both indices are associated with above-average summer precipitation in North China,while weaker values are associated with below-average summer precipitation.In cases where the strength of the two indices is inconsistent,regional precipitation in North China may be above average,but the overall precipitation in the entire region remains relatively normal.2)Anomalies in summer precipitation in North China result from the combined effects of the East Asian subtropical summer monsoon and the upward motion of atmospheric dynamics in North China.In years with stronger EAMI and HDBRI values,the Baikal Lake trough deepens at the 500 hPa level during summer,the Northwest Pacific subtropical high shifts northward,and North China falls under influence of a circulation pattern characterized by a high-pressure system in the east and a low-pressure system in the west.Consequently,the movement of the western low trough eastward is hindered,leading to a sustained upward motion of the atmosphere over North China.This pattern is accompanied by an increased intensity of the Indian summer monsoon and the East Asian subtropical summer monsoon at the 850 hPa level.During this period,the westerly wind water vapor transport from the tropical Indian Ocean,the southerly wind water vapor transport from the East Asian subtropical region,or the southeast wind water vapor transport strengthens,ensuring an ample supply of water vapor to North China.Such a configuration of high-and low-level circulations is highly conducive to generating increased summer precipitation in North China.Conversely,unusually below-average summer precipitation occurs when the aforementioned conditions are not met.3)The stronger values of the EAMI and HBDRI during the early April-May period can serve as climate monitoring and prediction indicators for abnormally high summer precipitation in North China.