Gaoyuan qixiang (Jun 2022)
Analysis of the Characteristics and Mechanism of a Regional Heavy Rain Event in Liaoning Province
Abstract
Using ERA5 reanalysis data, cloud characteristic parameters retrieved by FY-4A satellite data, wind and rainfall data of ground automatic weather stations, a regional rainstorm accompany with short-term heavy rainfall in southeastern Liaoning Province from May 17 to 19, 2020 is studied in detail.The results show that northeast cold vortex superimposed on the strong northward development of the cyclone is the main weather situation in this process.The short-term heavy rainfall occurs when the cold vortex is close to mature and the cyclone is strongly developed.The local ground convergent shear line is the mesoscale condition leading to short-term heavy precipitation.The water vapor transporting channel on the southeast side of the cold vortex merges with the water vapor transported to north through the South China Sea by the southwestern low-level jet on the east side of the tropical depression, which comes from Bengal Bay.This has become the necessary condition for the occurrence and maintenance of the rainstorm.The precipitation in the central and eastern part of Liaoning Province appears in the northeast-north-northwest region of the cold vortex system.The precipitation area has the highest correlation with the 850 hPa wind field.In the generation and maintenance stage of precipitation, the convergence area appears below 700 hPa, and the divergence occurs between 600 and 200 hPa.Where the rainfall intensity is greater than 5 mm·h-1, the updrafts ascend approximately upright through the whole wet layer.There is a dense pseudo equivalent potential temperature tilt above the precipitation areas toward the northwest, and a thermal instability exits below 400 hPa.The cold vortex develops to a mature stage, and the intrusion of dry and cold air makes the inner edge of cold vortex clouds clear gradually, forming a comma-shaped clouds.The heavy precipitation area is distributed in strips, the cloud top height is generally greater than 9 km, and the cloud optical thickness is greater than 60, which is a cold-warm mixed cloud with abundant hydrometeor content; The cloud optical thickness far away from the center of the cold vortex is less than 20, where the cloud is loose and belongs to a high-level cold cloud, and there is basically no precipitation on the ground.
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