The South China Sea Monsoon Experiment—Boundary Layer Height (SCSMEX-BLH): Experimental Design and Preliminary Results

Knowing the relationship between local convective precipitation and boundary layer processes is critical for forecasting rainstorms. For the South China Sea area, such a forecast is particularly important during the monsoon season. During such a season, the authors examined the boundary layer features at three sites as part of the South China Sea Monsoon Experiment—Boundary Layer Height (SCSMEX-BLH) experiment. The sites are spread from inland to over sea along a 43.4-km line. Here the authors analyze SCSMEX-BLH data from an intensive observing period that includes a convectively suppressed (inactive) period, a period influenced by a tropical storm, and a convectively active monsoon period. Some preliminary findings include the following: 1) The absorption of shortwave radiation over the sea is the primary driver of the land–sea temperature difference. The difference produces a diurnal variation below 400 m, with a warmer surface layer over the coast at night. 2) In the inactive and storm periods, the sensible heat flux is larger than that in the active period, whereas in the active period, the heat flux (primarily latent heat flux) over sea is significant. Also in the active period, the depth of the mixed layer inland is smaller than that in other periods, but the depth on the coast is always higher than that in other periods. 3) In the active period at night, as a monsoon vapor surge advects horizontally over the warm sea surface, a large latent heat flux driven by strong winds aids the growth of marine cumulus, which eventually develop into inland cumulonimbus bringing inland rainfall.