Contrasting Lightning Activity and Convective Structures between Tropical Cyclones over Open Ocean and Enclosed Sea

        Most tropical cyclones (TCs) landfalling Southern China originated from the Northwest Pacific (NWP) and tracked over the South China Sea (SCS) before landfall. The internal structures such as convective characteristics of the tropical cyclones may change as the TCs translate from the open ocean (NWP) to the enclosed sea (SCS) due likely to the impacts from nearby landmass. This study compares the lightning activity and convective structures, as well as the large-scale environments, of TCs over the NWP and SCS to better understand the structural changes and underlying physical mechanisms. It is interesting that TCs over SCS are much more electrically active than NWP TCs (especially in the outer rainbands), even though the NWP TCs precipitate heavier. Multi-satellite observations suggest that the NWP TCs have a deeper layer of ice particles, producing heavier surface rainfall; however, the SCS TCs own more large ice particles or supercool liquid in the mixed-phase region, which is essential for charge separation thus lightning production. It is surprising that the thermodynamic conditions (e.g., SST and atmospheric instability) of the NWP are more favorable for convective development than SCS. A few factors may contribute to higher lightning activity in SCS TCs, including stronger vertical wind shear, thinner warm cloud depth and higher aerosol optical depth, all may help to produce asymmetric intense convection and active mixed-phase processes. Furthermore, SCS TCs display a marked lightning maximum in the front quadrants of the moving direction, but NWP TCs are less so, likely because the thermodynamic and aerosol impacts from land are stronger in the SCS. Lightning in the SCS TCs is also more asymmetric relative to the vertical wind shear than the NWP TCs, which is featured by a maximum in the right of the downshear region of the outer rainband (opposite to the precipitation pattern).