A synthetic analysis of mesoscale precipitation system In northeastern China based on sattellite and radar data

On June 10^th , 2005 a serious mud-rock flow event occurred in Shalan river upper basin of Heilongjiang Province, northeastern China. The large-scale environmental condition and meso-scale precipitation systems (MPSs ) related to heavy rain process caused the disaster event are studied based on conventional observations as well as satellite and radar data. An elementary diagnosis is performed to the large scale circulation，the stratified evolution，the underlying surface condition and the meso-scale precipitation systems. To be summarized, the findings from the analyses are as follows: the rainstorm occurred in front of a upper level trough, which has a forward tilting and a diverging dispersive structure. MPSs are distributed in the foreside area of this upper air trough with divergence at the upper level and convergence at the lower level of the troposphere. Viewing from stratification characteristics of temperature and humidity, a SW-NE oriented moist tongue located at the lower level of troposphere was obviously seen before the rainstorm occurs, which feeds the rainfall area with favorable moisture condition. Furthermore, the differential advection induced by dry and cold air superposing the warm and moist air results in the increase in local instability. The distribution of incoming solar irradiance at underlying surface shows differential heating which is an important trigger to the MPSs of this rainstorm. With respect to the relationship between meso-scale shear line and the MPSs, it is found that over the shear line，the convective cells located near the highest curvature area of the shear line are the most intense. It is suggested that this is related with the orientations between the surface mesoscale shear line and the ambient wind fields.

Based on the results identified in above analysis, study on dynamical structural characteristics of the MPS which induced the rainstorm, which aim at furthering the understandings to the MPSs of rainstorm over Northeastern China, is further performed in this paper by using Doppler radar and satellite observational data. The present analysis indicates that the MPS is an isolated convective system having multi-cell storm structure and it is the rapid growth of some convection cells in the MPS that directly induced the Shalan river basin rainstorm. Furthermore, the research also reveals that low-level wind fields corresponding to the MPS during its nascent, developing and mature phases vary rhythmically. With rainfall increasing, the anti-cyclonic divergence of the low-level wind fields over the surface rainfall region goes up, which may be a demonstration of the increment in the thunderstorm high. Taking the movement direction (north east) of the system as front, warm and moist updrafts are input on the left back (westerly) part of the cloud while downdrafts are output on the right front (easterly) part. That is, as for the whole system, it is characterized by a backward input and forward output structure. As regard to the movement characteristics of the convective system, this MPS belongs to a left moving storm.

Key words: serious mud-rock flow event, meso-scale precipitation systems (MPSs ), satellite and radar data analysis, multi-cell storm, left moving storm

Fig. 1 The TT index distribution chart of 08BST June 10th, 2005 (Unit: ℃)

Fig.2 Solar energy received by underlying surface at 08BST and 09BST June 10^th,2005 (Unit:W/m^{) (According to the FY-2C geosynchronous satellite solar irradiance product)}

(a) Echoes at 3km (Unit: dbz) (b) wind fields at 1.5km (Unit:m/s)

(c) Cross-section in WE direction (d) Composite map of echoes and u-w

Stream fields at 1.5km wind fields

Fig.3 Radar echoes and wind fields retrieved by radar at 11:48BST on June 10^th,2005