Analysis of the Mesoscale Characteristics of an Unusually Heavy Rain on May 8,2014 in Guangdong

Based on the 1° × 1° reanalysis data from NCEP / NCAR,conventional surface observations,and TBB data from the FY-2E weather satellite,a warm-sector torrential rain that happened on May 8- 9,2014 in the southern part of South China was studied.The result is presented as follows.( 1) The first stage of the rain happened at the rear part of a transformed high ridge and was affected by cold air,belonging to the type of torrential rain caused by a return airflow in the warm sector,which is typical of South China.The second stage of the rain,however,was triggered by weak cold air from an eastward route,belonging to the type of torrential rain that is not caused by a return airflow.( 2) This process of torrential rain was directly caused by a meso-α scale MCC and a meso-β scale MCS,in which an MCS-D was formed over Guangxi and moved eastward gradually and multiple convective systems merged to prolong the lifecycle of the MCS-D to result in the generation of the meso-α scale MCC.( 3) A southeasterly flow was the main supplier of water vapor for this torrential rain.The intrusion of small-scale dry and cold air at mid-level,intense divergence at high levels and deep ascending motion were so allocated that mesoscale convective systems developed and maintained.( 4) As shown in an analysis of a wind field data from regional automatic weather stations,nighttime land wind( a northerly) converges with a strengthened southeasterly wind near 112.5°E,possibly intriguing the generation of an MβCS-H,a mesoscale convective system.