2023年河南麦收连阴雨的形成和环流异常分析

Analysis of Causes and Circulation Anomaly of the Continuous Rain in Wheat Harvest Season 2023

2023年5月25—30日河南遭遇了1961年以来同期持续时间最长、影响最大的连阴雨天气过程。连阴雨天气导致小麦大幅减产,品质下降,豫南、豫中和豫东部分种子田失去种用价值,被评为“烂场雨”。利用常规观测资料、NCEP再分析资料和EC数值预报产品,对这次连阴雨过程的大尺度环流形势和影响系统进行分析。结果表明:(1)该天气过程发生在异常大气环流背景下,西太平洋副热带高压显著偏强,脊线5天滑动平均位置偏北达8个纬度,越过25°N线;西伯利亚高压也显著偏强且频繁向南暴发。(2)乌拉尔山阻塞系统的形成导致我国新疆西北部长时间维持一深厚冷涡,从而在35°—40°N形成了稳定纬向环流,冷涡底部不断有冷空气分裂东移南下影响河南。远距离超强台风的逼近导致副热带高压迅速西伸北抬,在其外围形成了一条宽广、深厚的从南海伸向中纬度地区的暖湿气流输送带,最终在豫西北汇聚出低空急流。随着暖湿气流输送带向北扩展,在大风速区的前方,对流层中低部有明显的空气质量和水汽的辐合,从而引发上升运动的发生发展,导致多地暴雨、局部大暴雨的出现。(3)南北两个异常的天气系统的结合,促成了中纬度能量锋区的稳定维持,锋面抬升对暖区降水起到增幅和维持作用。(4)数值模式对中、短期环流趋势和影响系统均作出了较准确的预报,但对降水量级及其分布的预测还需要进一步推敲订正。

The continuous rain process in Henan Province from 25 to 30 May 2023,which had the longest duration and heavies impact in the same period since 1961,led to a significant reduction in wheat yield and quality,making some seed fields in southern,central and eastern Henan lose their planting values,so this rain event is known as“rotten field rain”.In this article,the large-scale circulation situation and impact system are analyzed based on the MICAPS conventional observation,NCEP reanalysis data and ECMWF numerical prediction products.The results are as follows:(1)This continuous rain event occurred in the background of abnormal atmospheric circulation.The western Pacific subtropical high was significantly stronger and the 5 d moving average position of the ridge line was 8 latitudes northward,crossing the 25°N line.At the same time,the Siberian High was also unusually strong and active towards the south.(2)A deep cold vortex from the Ural Mountains blocking System that maintained for a long time in the northwest of Xinjiang,China,caused the formation of a stable zonal circulation in 35°40°N,which brought about cold air constantly splitting from the bottom of the cold vortex,moving to southeast and affecting Henan from west to east.The western Pacific subtropical high rapidly jumped to north and extended to the west as a long-distance super typhoon approached,forming a broad and deep conveyor belt of warm and humid air extending from the South China Sea to the mid-latitudes in its periphery,and finally converging into a low-level jet stream in the northwest of Henan province.With the warm and humid airflow spreading to the north,there were obvious convergence of air mass and water vapor in low-troposphere in front of the high wind speed zone,causing the developing of ascending motion,which led to the occurrence of rainstorm in many places and localized severe rainstorm.(3)The encounter of two anomalous weather systems in the north and south contributed to the stable maintenance of the mid-latitude energy front zone,and the frontal uplift increased and maintained precipitation in the warm section.(4)The numerical models have made accurate forecasts of the medium-and short-term circulation trends and the impact systems,but the forecast of precipitation magnitude and its distribution needs to be further refined.