Diabatic heating structures varying with convective and rainfall intensities in different areas of the pan-South China Sea region

Abstract

This study investigates and compares diabatic heating structures related to vertical velocity, cloud types, and rainfall intensities in the northeast rainy sea subregion named Dongsha, the west rainless sea subregion named Xisha, and the north rainy land subregion named Coastland in the pan-SCS region. The diabatic heating rate of >2 K hr−1 over Dongsha and Coastland has a higher frequency and a deeper distribution than over Xisha where it requires stronger upward motion to achieve the same heating rate, indicating more frequent and deeper convection over the north coastal sea and land areas than the west sea area of the pan-SCS region. The deep convective Q1 profiles show a stronger peak at ~500 hPa and a weaker peak at ~700 hPa over two sea subregions while a single peak at ~500 hPa over Coastland. The nimbostratus Q1 profile has a weakened heating peak at 350–550 hPa over Dongsha, 500–600 hPa over Xisha, and 425–575 hPa over Coastland. The shallow cumulus Q1 profile of Dongsha shows weak heating in the mid-to-lower troposphere while that of Xisha and Coastland has hardly heating. Latent heating and vertical turbulence significantly affect the diabatic heating structure related to deep convective clouds and nimbostratus but hardly affect that related to shallow cumulus. Despite cloud types, Dongsha has the strongest diabatic heating among the three subregions due to its geographical advantages. The no-rainfall Q1 profiles over three subregions have a similar shape with a weak cooling peak at ~700 hPa due to boundary-layer evaporation and eddies. But the small-rainfall Q1 profiles present upper heating and lower cooling over sea subregions whereas the opposite over Coastland possibly due to stronger surface sensible heating on the land. From moderate to heavy rainfall, the Q1 profiles over three subregions are similar with a heating maximum at ~500 hPa associated with deep convection, except for heating intensity which is much stronger over Xisha than the other two subregions. This suggests that Xisha presents stronger convection to achieve the same rainfall intensity as Dongsha and Coastland, which is closely due to a positive effect of coastal terrain blocking and uplifting on precipitation for Dongsha and Coastland whereas a negative effect of the Annam Mountains for Xisha.