Diagnostic Study of Apparent Heat Sources and Moisture Sinks in the South China Sea and its Adjacent Areas during the Onset of 1998 SCS Monsoon

The apparent heat sources (?Q1 ?) and moisture sinks (?Q2 ?) are calculated based on the reanalyzed data of the South China Sea Monsoon Experiment (SCSMEX) from May 1 to August 31, 1998. It is found that the formation and distribution of the atmospheric heat sources are important for the monsoon onset. The earlier onset of the SCS monsoon is the result of enduring atmospheric heating in the Indo–China Peninsula and South China areas. The atmospheric heating firstly appears in the Indo–China Peninsula area and the sensible heat is the major one. The 30–50 day periodic oscillation of atmospheric heat sources between the SCS area and the western Pacific warm pool has a reverse phase distribution before the middle of July and the low frequency oscillation of heat sources in SCS area has an obvious longitudinal propagation. The 30–50 day low frequency oscillation has vital modificatory effects on the summer monsoon evolution during 1998. Key words Apparent heat sources - Apparent moisture sinks - The South China Sea monsoon - Diagnostic Study Sponsored by the National Key Project of Fundamental Research “ SCSMEX” and the Research Fund for the Doctoral Program of Higher Education: “ Study of the Air-sea Interaction in the SCS Monsoon Region”.

A Study on the Mesoscale Convective Systems during the Summer Monsoon Onset over the South China Sea in 1998 Part II: Effect of Mesoscale Convective Systems on Large-Scale Fields

The apparent heat sources and apparent moisture sinks, and large-scale wind,temperature as well as the surface pressure fields during the summer monsoon onset over the northernSouth China Sea (SCS) in 1998 were diagnosed. The results suggested that there was a kind ofpositive feedback mechanism between large-scale circulations and mesoscale convective systems(MCSs). Before the monsoon onset, the large-scale background provided favorable synoptic and dynamicconditions for the summer monsoon onset and the formation of mesoscale convective activities,whereas after the summer monsoon onset, occurrence of the persistent and extensive mesoscaleconvective activities produced obvious feedback effect on large-scale circulations. Because of therelease of latent heating produced by enhanced convective activities, the intense atmosphericheating appeared over the northern SCS, which resulted in: (1) the meridional temperature gradientover the SCS reversed from upper-level to low-level and then the large-scale circulations werechanged seasonally; (2) correspondingly, the surface pressure over the northern SCS deepenedcontinually and formed a broad monsoon trough and the obvious pressure-fall areas, thus making thesubtropical high move out of the SCS eventually; (3) with the development of the low pressurecirculations in the middle and low troposphere, the MCSs further enhanced and extended southward,which was conducive to the SCS monsoon onset and maintenance over the middle and southern SCS; and(4) the deepening of monsoon trough facilitated the monsoon flow and moisture transport on itssouthern side, thus the monsoon onset reaching peak period.

NATURE OF PRECIPITATION AND ACTIVITY OF CUMULUS CONVECTION DURING THE 1991 MEIYU SEASON OF CHANGJIANG-HUAIHE RIVER BASIN

Seasonal variability regarding the nature of precipitation and the activity of cumulus convection during the 1991 Meiyu season of Changjiang-Huaihe River Basin(Jianghuai)has been investigated by calculating apparent heat source/apparent moisture sink and analyzing TBB(cloud-top blackbody radiation temperature)data.It is found that three periods of strong ascending motion during the Meiyu season lead to three episodes of heavy rain,and the latent heat due to the precipitation is of the sole heat source of the atmosphere.The nature of precipitation shows distinct seasonal variability,from frontal precipitation of the first episode to the extremely strong convective precipitation of the third episode.TBB field of East Asia may well reflect not only the intensity of convection and rainfall,but also the movement of rain belt and convection belt.In the whole Meiyu season.convection belt mainly stays in Jianghuai.but may shift within the domain of East Asia.Its locating in Jianghuai or not determines the maintenance or break of Meiyu.In the third episode,the narrow convection belt over Jianghuai is mainly caused by southwest monsoon which takes moist and convective atmosphere from tropical ocean.