2017年秋季四川阴雨寡照特征及成因分析

Analysis of Autumn Rainy and Sunless Characteristics and Its Mechanism in Sichuan in 2017

利用四川省气象台站逐日降水、日照时数资料,NCEP/NCAR逐日及逐月再分析资料和NOAA提供的月平均海表温度资料,通过现代学统计方法研究了2017年秋季四川阴雨寡照的主要特征及其成因。结果表明:2017年9-10月四川秋绵雨天气特征明显,呈现出雨日偏多、日照偏少、阴雨寡照持续时间长等特点。9月对流层中层贝加尔湖至巴尔喀什湖地区上空为宽广倾斜的低压槽,有利于冷空气东移南下影响四川,同时西太平洋副热带高压偏强西伸,冷暖空气交汇于四川上空,形成持续性降水。10月对流层中层西太平洋副热带高压偏北偏西偏强和印缅槽加深共同作用,有利于来自孟加拉湾和西太平洋的水汽向四川输送,为四川带来持续性降水。进一步分析发现,9月Rossby波能量频散特征有利欧亚中高纬环流的持续和维持,能量频散是巴尔喀什湖至贝加尔湖地区上空低压槽稳定维持的重要原因。此外,9-10月赤道中东太平洋海温明显偏低,且不断加强发展,是西太平洋副热带高压偏强偏西偏北和印缅槽偏深的重要外强迫源。因此,由海温外强迫和Rossby波能量频散造成的大气环流异常,导致了9-10月四川秋雨期阴雨寡照天气的持续。

Based on the observed daily precipitation and sunshine hour data in Sichuan Province,the NCEP/NCAR reanalysis daily and monthly data,and the NOAA monthly sea surface temperature data,the variation characteristics of the autumn rainy and sunless weather and its mechanism of the Sichuan in 2017 have been analyzed by the modern statistics methods in this paper.The results showed that the stage characteristics of autumn rain in Sichuan from September to October of 2017 were obvious,showing the characteristics of more rainy days,less sunshine and longer duration of rainy and sunless weather.The area between Baykal Lake and Balkhash Lake was under a wide and inclined low trough in the middle layer of troposphere,which is beneficial to the movement of cold airflow to the southeast,influencing Sichuan.At the same time,the Western Pacific subtropical high was stronger,stretching more westward than normal,and finally the cold and warm airflows met in Sichuan and formed continuous precipitation in September.In October,the Western Pacific subtropical high was stronger,stretching more westward and northward than normal,while the Indian-Burma trough was deeper at 500 hPa,which is beneficial to the water vapor transport to Sichuan from Bay of Bengal and Western Pacific.This is favorable for the continuous precipitation in Sichuan.Further analysis showed that the characteristics of Rossby wave propagation is beneficial to the continuation and maintenance of the Eurasian circulation in the middle and high latitudes,and the Rossby wave energy dispersion is an important cause of maintaining the low trough on the area between Baykal Lake and Balkhash Lake in September.In addition,the sea surface temperature in the equatorial central and eastern Pacific obviously continues to be lower,making the Western Pacific subtropical high become stronger,stretching more westward and northward and Indian-Burma trough was deeper than normal from September to October.Therefore,the influence of the external forcing signal of sea surface temperature and the circulation anomaly caused by the Rossby wave energy dispersion led to the persistence of rainy and sunless weather in Sichuan from September to October of 2017.