新气候态时段华西秋雨变化特征及海气影响分析

Analysis of Change Characteristics and Air-Sea Impact of Western China Autumn Rain During New Climate State Period

摘要:

利用1981—2022年华西地区373个气象台站和ERA5再分析资料，使用Mann-Kendall、相关和合成等方法分析了进入新气候态时段（1991—2020年）后华西秋雨变化特征，并探讨其大气环流和海温异常特征。结果表明：华西秋雨于2011年发生了明显由少转多的突变。欧洲西岸至乌拉尔山附近和鄂霍次克海地区阻塞高压（下称鄂海阻高）加强、西太平洋副热带高压（下称西太副高）加强西伸和水汽条件配合等，为其由少转多提供了有利条件。海温场分析表明：前期春、夏季及同期秋季印度洋海温由冷转暖和中太平洋海温由暖转冷，引起中低纬度对流活动和经向环流发生调整，导致西太副高发生由弱到强、显著西伸的变化。西北太平洋海温异常偏暖通过激发经向遥相关波列，使鄂海阻高加强。西大西洋海温偏暖使阿拉伯海至孟加拉湾地区对流活动增强。上述区域海温变化共同致西太副高西侧及孟加拉湾输送至华西地区的水汽由弱变强，从而导致华西秋雨由少转多。

Abstract:

Using data from 373 meteorological stations in the Western China region and ERA5 reanalysis data from 1981 to 2022, this study employs methods such as Mann-Kendall, correlation, and composites to analyse the characteristics of autumn rainfall changes in Western China after entering a new climatic phase, and explores the atmospheric circulation and sea temperature anomaly characteristics. The results indicate that over the past 32 years, the overall trend of Western China autumn rain significantly increases, with an increase in precipitation of approximately 30.4 mm, at a rate of about 9.5 mm per decade. Spatially, most areas show an increase post-shift, with significant increases primarily located in most of the Sichuan Basin, western Hunan, southern Shanxi, and southern Ningxia regions. Circulation field analysis reveals that since 2011, the blocking high near the western coast of Europe to the Ural Mountains and the Sea of Okhotsk area (hereafter referred to as the Okhotsk high) strengthens. The Western Pacific Subtropical High (hereafter referred to as the West Pacific Sub-high) also intensifies and extends westward. The southwesterly winds turning through the South China Sea from the subtropical region of the Western Pacific, the easterlies from the Northwest Pacific region, and the southwesterly winds from the Indian Ocean through the Bay of Bengal all strengthen. These factors collectively contribute to an increasing trend in water vapour transported to Southwestern, providing favourable conditions for the transition from lesser to greater autumn rainfall. Sea surface field analysis indicates that during the earlier spring and summer, as well as the concurrent autumn seasons, sea temperatures in the Indian Ocean transition from cold to warm, while sea temperatures in the central Pacific shift from warm to cold. These shifts prompt adjustments in convective activity and meridional circulation across the mid-low latitudes. These also lead to a shift in the West Pacific Sub-high from weak to strong, markedly extending westward, enhancing the intensity of water vapour transported from its western side and the Bay of Bengal to Southwestern. Anomalous warming in the Northwest Pacific Ocean, by stimulating meridional teleconnection wave trains, strengthens the Okhotsk high. Elevated sea temperatures in the western Atlantic increase convective activity from the Arabian Sea to the Bay of Bengal, which, through downstream propagation of teleconnection wave trains, facilitates the transport of water vapour from the Bay of Bengal to Southwestern. The combined sea temperature changes in these regions thus intensify the water vapour transport from the western side of the West Pacific Sub-high and the Bay of Bengal to Southwestern, consequently leading to an increase in autumn rainfall from lesser to greater amounts.