Analysis of the linear mesoscale convective systems during the meiyu period in the middle and lower reaches of the Yangtze River. Part Ⅰ: Organization mode features.

Using the composite radar reflectivity data and operational observation data, the mesoscale convective system (MCS) that occurred in the middle and lower reaches of the Yangtze River in June and July 2010 are investigated. The numbers of the line MCS are more than the numbers of the nonline-MCS. There are eight identified classes line-MCS: Trailing stratiform MCS （TS), Leading-stratiform-MCS(LS),Training-line/Adjoiningstratiform MCS (TL/AS), Backbuilding/Quasi-stationary MCS (BB), Parallel stratiform MCS (PS), Broken line MCS (BL), Embedded line MCS (EL) and Long line MCS (LL), and six of them are the same as the previous classifyed archetype, but the embedding line MCS and the long zonal stratiform MCS are the new statistical classes in the middle and lower reaches of Yangtze river during the meiyu period. The TS，LS，PS and BL classes are movable during their life period, while the TL/AS, BB, EL and LL ones are immovable. The average lasting time of the line MCS is greater than 7 hours. The MCSs usually develop along the Yangtze River, with the more frequently occurring areas of the MCS located north of Chongqing city, in the Jianhan plain, south of Anhui Province and over the Dabie mountain. The MCSs move eastward, northeastward, southeastward or southward, and the moving track of the line MCS is related to the steering flow of its environmental field. Diurnal variations of the MCS are of several peaks during its early stages, while in mature stages, the occurring strong precipitation probabilities are distinctly larger from afternoons to nights than from late nights to mornings.