Regional distribution and diurnal variation of deep convective systems over the Asian monsoon region

Abstract

Using 12 years of data from the Tropical Rainfall Measuring Mission (TRMM)-based Precipitation Radar (PR), spatial and diurnal variations of deep convective systems (DCSs) over the Asian monsoon region are analyzed. The DCSs are defined by a 20 dBZ echo top extending 14 km. The spatial distribution of DCSs genesis is also discussed, with reference to the National Centers for Environmental Prediction (NCEP) reanalysis data. The results show that DCSs occur mainly over land. They concentrate in south of 20°N during the pre-monsoon season, and then move distinctly to mid-latitude regions, with the most active region on the south slope of the Himalayas during monsoon season. DCSs over the Tibetan Plateau are more frequent than those in central-eastern China, but smaller in horizontal scale and weaker in convective intensity. DCSs in central-eastern China have more robust updrafts and generate more lightning flashes than in other Asian monsoon regions. The horizontal scale of DCSs over the ocean is larger than that over the other regions, and the corresponding minimum infrared (IR) brightness temperature is lower, whereas the convective intensity is weaker. Continental DCSs are more common from noon through midnight, and DCSs over the Tibetan Plateau are more frequently from noon through evening. Oceanic DCSs frequency has a weaker diurnal cycle with dawn maximum, and diurnal variation of DCSs over the tropical maritime continent is consistent with that over the continent.