华北夏季入海中尺度对流系统的时空分布及环流特征分析OA

Utilizing summertime multi-S-band operational radar mosaic data(2016-2018)over North China,GPM-IMERG(Integrated Multi-satellite Retrievals for Global Precipitation Measurement)satellite land-sea mask data,this study develops a set of objective identification criteria for offshore-propagating MCSs based on dynamic underlying surface properties.Building upon this,the statistical characteristics of offshore-propagating and non-offshore-propagating MCS are analyzed,and the north-south differences in the large-scale circulation background and environmental driving mechanisms for offshore-propagating MCS over North China are revealed.The principal conclusions are as follows.(1)The established objective identification criteria effectively capture the dynamic process of MCS crossing the coastline.Statistics show that offshore-propagating MCS samples are characterized by being"less frequent but more intense".(2)During the occurrence of offshore-propagating MCSs,North China is located within a strong upper-level divergence area to the right of the 200 hPa jet entrance region.The mid-to-lower troposphere exhibits stronger baroclinicity,and the environmental fields feature significantly higher Most Unstable Convective Available Potential Energy(MUCAPE)and vertical wind shear,providing favorable conditions for the organization and maintenance of convection.(3)Significant north-south differences exist in the driving mechanisms for MCS offshore propagation over North China:The northern Bohai Sea region belongs to the"dynamic guidance type",where systems are steered southeastward into the sea by a 500 hPa shortwave trough.Post-trough dry,cold air advection at 700 hPa enhances convective instability,and strong vertical wind shear helps balance the cold pool outflow,sustaining the system's offshore propagation.In contrast,the southern Bohai Sea region is characterized as the"warm-moist advection type,"driven by a robust 700 hPa southwesterly low-level jet(LLJ).The LLJ not only provides steering but also continuously transports energy and moisture,supporting the system's northeastward extension within a warm and moist background.This research not only advances the physical understanding of convective system evolution across the land-sea transition zone but also provides a technical foundation and new perspectives for future studies on the mechanisms governing MCS offshore evolution.Furthermore,it offers objective guidance for the operational forecasting of severe convective weather in coastal regions.