The semi-diurnal cycle of deep convective systems over Eastern China and its surrounding seas in summer based on an automatic tracking algorithm

摘要

Deep convective systems (DCSs) are associated with severe weather events and can affect regional and global climate. To study the semi-diurnal variation of DCSs over Eastern China and its surrounding seas in summer, we modified the Tracking of Organized Convection Algorithm through a 3-D segmentatioN (TOOCAN) by employing Himawari-8 operational cloud property (CLP) products instead of original infrared images, and renamed the algorithm as TOOCAN-CLP. The DCSs detected over land and sea are divided into small-, medium-, and large-sized classes based on the convective core equivalent radius. The small and medium-sized DCSs over land exhibit a maximum occurrence in the afternoon, which is associated with local thermal instability and sea breeze circulation. The occurrence of small DCSs over the tropical sea areas varies analogously to that of small continental DCSs but with a smaller amplitude. However, medium-sized DCSs over the sea, which account for the majority of DCSs over the sea, exhibit weak semi-diurnal variability. Large DCSs over inland China and its surrounding seas tend to initiate at night and decay in the daytime. The generation of large DCSs over inland China at night is mainly due to the enhanced transport of warm and moist air by strong large-scale prevailing southerly or southwesterly winds, while the large offshore DCSs accompanied by heavy rainfall is closely associated with the interaction between local offshore breeze and large-scale monsoon flows, as well as gravity waves.