Analysis Of Mesoscale Convective System (MCS) Initiation In Central-eastern China

Mesoscale convective systems frequently occur in central-eastern China(110-124°E,27-40°N). Severe convection weather caused by MCS in summer gave rise to the countlessdisaster that threatened local people’s life and property security and brought serious economic lossevery year. It seemed to have been particularly difficult for whether MCS happened; from theradar and satellite cloud pictures, we can monitor the initiation and development of convectivesystem, but it’s difficult for objective estimating whether the primary thunderstorm system candevelop and organize into the MCS. In this paper, to this problem, there is much analysis anddiscussion. This article summarized the mesoscale convective system research in recent years,included generalizing the definition, identification standard, the geographical distribution and lifecharacteristic, development stage characteristic, structure and evolution characteristic and theinitiation circulation background for MCS etc., which are done research by scholars at home andabroad. First, MCSs of all shapes and sizes were objectively identified and analysed for thegeographical distribution and life characteristic. Then, environment of the day without MCS and6h prior to MCS initiation were chosen for analysis. At the end, typical parameters were selectedby comparing the different conditions for the widespread convection and MCS. It’s hoped that thepicked better physical parameters during many physical parameters derived from the key factorsforming MCS are able to forecast the MCS objectively.First, Based on the FY-2geostationary satellite infrared digital cloud images during summertime（June-August）of2008-2010, the space and time characteristic of mesoscale convectivesystems were investigated in central-eastern China (110-124°E,27-40°N). According to size, theclassification scheme used for this study includes two previously defined categories: meso-αmesoscale: meso-α mesoscale convective system(MαCS) and meso-β mesoscale convectivesystem(MβCS). Then on the basis of the shape, MαCSs were classified mesoscale convective complexs(MCC) and persistent elongated convective systems(PECS), MβCSs were classifiedmeso-β circular convective systems (MβCCS) and meso-β elongated convective systems(MβECS). The result reveals:(1) There are208MCSs in summer during the three years, including68MαCSs and140MβCSs. Elongated systems accounted for79.3％of the total MCS samplewhich indicates the elongated systems were the most common type of MCS in summer in thisregion.(2) On the whole, most MCSs moved from the west to the east and some from the south tothe north or the north to the south, and it’s consistent with the moving weather system ofmid-latitude westerly in China.(3) The peak time of MCS initiation is between0900and1000UTC, and most MCSs reached their maximum size between1000and1100UTC. Most of thesystems dissipated between1200and1300UTC. The life scale of MCS is about6.5hours.(4)MαCSs from the initiation to mature stage need about three to four hours, while from mature totermination phase should last for about four to five hours; And for MβCSs, the developing andweakening stage have the same time about two to three hours.Then, the fixed-point composites for conditions between63days without MCS selected byprimary satellite datasets and64of208MCSs were estimated by data of NCEP reanalysis withtemporal resolution1°×1°and time resolution6hours that were taken at about6h prior todevelopment at initiation in summer from2008to2010. The result shows that it’s significantlydifferent in condition between the two kinds of system:(1) At middle and low troposphere it’ssouthwest flow, strong wind and there is warm advection near the genesis position where existsshear line at the upstream; There is significant upper level jet in the north of the genesis region;The west Pacific subtropical high is stronger and strengthen westward expansion; The South AsiaHigh is stronger and strengthen eastward expansion.(2) At low levels, there exists positivevorticity that is in the northwest of genesis position and convergence; At high levels, there existsnegative vorticity and divergence; Low-level vapor transported from the Bay of Bengal and theSouth China Sea gathered at middle and low troposphere.(3) It appears obvious unstablestratification at low-level, neutral at mid-level and stability at high-level. Convective instabilityincreases from north to south.At the end, the174widespread convection that is defined as a highly concentrated group ofthunderstorms that does not ungergo upscale growth and organization into an MCS were identifiedby artificial with the same satellite data which used in previous chapter. To obtain the differentdatasets to identify features important to MCS developing from the widespread convection, onemethod used in this analysis involved simply taking a single value of a given field for theprecursor environment of208MCSs at about6h prior to development at initiation and for the174cases of widespread convection at the time of the maximum number of convective cells by NCEP reanalysis data. Strom-relative composites were created to find out the essential parameters todistinguish the two systems. At last, an objective method called dichotomous forecast (HSS, POD,FAR, TS, BS) was also implemented to test the skill and accuracy of the various parameters inforecasting MCSs. As a result, we found out about seven parameters better forecasting MCSs,they are the SWEAT, MK, LFTXS, surface2m specific humidity,850hPa relative humidity andtemperature advection and0-3km vertical wind shear.