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Analysis on a Meso-scale Convective Complex over Central Hebei Province

Author: FanJunHong
Tutor: GaoZhiQiu；TianWenShou
School: Lanzhou University
Course: Meteorology
Keywords: MCC satellite image characteristic environmental condition physics mechanism numerical simulation
CLC: P458.121.1
Type: Master's thesis
Year: 2008
Downloads: 68
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Abstract


Mesoscale convective system（MCS）and Mesoscale convective complex play important role on torrential rain and severe convective weather include hail,gale and thunderstorm in summer season,so the study on its environment conditions,satellite image characteristics ,structure,physics mechanism and so on are essential.A MCC is analyzed which occurred in central Hebei Province at night July 30,2007,using 1°×1°reanalyzed material, FY2 infrared images and TBB materials,doppler radar material, sounding data,precipitation and wind data by AWS .finally the numerical simulation is made by MM53.6.Results are as follows:（1）The MCC is produced by a combination of three convective cloud clusters.The charactistics of meso-βare maintained on a even meso-αanvil,and does the precipitation intensity of≥10mm..pricipitation .The heavy rain mainly occours during the periods of development and mature of MCC.（2） The MCC is located in the low pressure ahead of a cold front ,accompanied by a short wave moving from west to east on the level of 500hPa.The souther low level jet transports the moist and warm air,and the warm moist advection is a main forcing factor to produce MCC which easily forms in the region with big wind gradient ahead of the center of low level jet. The warm core occurs , the cyclone vorticity increases and the divergence alternates with height in the middle-level at the forming stage of MCC,and the levels of ascending motion are thick.（3）Based on mesoscale filtering method,the cyclonic circulation is presented on the level of 500hPa ,meanwhile the divergence outflow occours both on the low-level and high-level during the forming period of MCC,accordingly the positive temperature anomaly is on the middle level,and the negative anomaly both on the low-level and high-level.This is due to the development of deep convection.The latent heating makes warm-core on the middle-level,and the moist cold downdraft makes the cold pool from the boundary layer to surface.（4） The cold air with high value of MPV sliding along abrupt isentropic surface will pass through the environmental air with a stability gradually decreased,Based upon the conservation principal of moist potential vorticity ,the absolute vorticity will continuously increase,thus make MCC developed.The cold air which leads to the formation of MCC is from the middle level.（5）When the weak cold air triggers the convective unstable energy.MCC will form,When MCC is in the period of mature ,the higher level is neutral or stable.Due to the symmetric instability ,the slantwise updraft strengthen the convective updraft.During the mature period of MCC,a pair of positive and negative values of mpv2 presented,and their values are almost equal ,and the negative value of mpv2 is in the upper part（6）The MM5 outputs reveal that the center of jet of lower level presents ladder form in vertical direction,which strengthen the ascending motion.The relative positionbetween heavy rain and mesoscale jet on the levels of 600hPa and 700hPa changeswith different period of MCC,but is stable with mesoscale jet on the level of950hPa,and the heavy rainfall is always in the front end of the mesoscale jet on thelevel of 950hPa.（7）The heavy rainfall center depends on the wind direction of mesoscale jet.If it issouthwesterly, the heavy rainfall will be in the right- fron ,left-front when it issouthesterly.（8）The radar echo intensity is uniform with some linear cumulus during the matureperiod of MCC.Based upon EVAD method,the height of main divergence and verticalvelocity calculated by radar raw data is higher than that by MM5,but can refect thedynamics characteristics basically.

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CLC: > Astronomy,Earth Sciences > Atmospheric science (meteorology ) > Weather Forecast > Weather analysis of the process > Profile analysis > Individual analysis > Analysis of the precipitation process > Analysis of torrential rain
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