THE ORGANIZATION OF OCEANIC CONVECTION DURING THE ONSET OF THE EAST ASIAN SUMMER MONSOON

摘要

A preliminary analysis of radar data from the BMRC C-POL radar on Dongsha Island from 15 to 25 May, 1998 — a ten-day period following the onset of the East Asian summer monsoon over the northern South China Sea - reveals that lower and middle level vertical shears exert a dominant control over the structure and orientation of mesoscale convective systems in this region. The findings are consistent with those of LeMone et al. (1998) for TOGA CO ARE,. except two new organizational modes have been identified: weak, shear-parallel bands (2r in Fig. 1) for strong low-level shear and weak midlevel shear when the air is dry aloft, and shear-parallel bands (4c) for strong shears in both layers when the shear vectors are in the same direction. Midlatitude influences likely contributed to these two additional modes by producing strong westerlies (in the case of 4c) during the passage of a strong upper-level trough and midtropospheric drying (in the case of 2r) following passage of the trough. The average stratiform rain fraction for the onset period (25%) is much less than that reported for the Tropics as a whole (～40%), but is consistent with the recent modeling results of Tao et al. (2003).