Characteristics and cause analysis of Meiyu anomaly over Hubei Province in 2020

Abstract

By using Hubei Meiyu monitoring data, NCC new indices and NCEP/NCAR circulation reanalysis data, the characteristics and cause analysis of abnormal Meiyu over Hubei Province in 2020 are analyzed. (1) The results show that Meiyu in 2020 is abnormal with a longer duration and more precipitation. The duration is 54 days, only second to 1996. The anomalous characteristics of Meiyu in 2020 are more precipitation, strong intensity and rainy day rate, all taking the first place since 1961. (2) The early transitions of circulations from winter pattern to summer pattern, such as westerly jet, subtropical high and summer monsoon, result in the early onset of Meiyu. The late outset of Meiyu is induced by the late northward jump of the upper westerly jet and subtropical high in late July. Early onset and late outset lead to abnormal long duration of Meiyu in 2020. (3) The decay of El Niño event appears in the previous winter, while the persistent warming of the Indian Ocean basin-wide mode and negative phase of North Atlantic Triple index appear in spring and summer. With the background of such sea surface temperature anomalies, meridional circulation in mid- and high-latitude develops, resulting in active cold air. The subtropical high is strong and persists, and water vapor transport over its west side is strong too. The abnormally strong water vapor transport intersects with active cold air over the Lower Yangtze Region, resulting in abnormal precipitation of Hubei Meiyu.

Keywords

• abnormal meiyu
• meridional circulation in middle and high latitudes
• sea surface temperature anomalies
• north atlantic triple index
• water vapor transport