Abstract:Based on conventional and unconventional observation data, and with squall lines preceding tropical cyclone caused by two typhoons (Typhoon 201409 Rammasun and Typhoon 200606 Prapiroon) of great intensity differences in inland (Hunan Province and Jiangxi Province) as analysis objects, we diagnosed reasons of differences from the aspects of observation, large scale circulation background and difference stages of squall line. Our contrastive analysis focused on environmental circumstances of initial stage, surface mesoscale characteristics and vertical structure of mature stage. The results show that inverted typhoon trough and subtropical high lead to the squall line preceding Rammasun, while squall line preceding Prapiroon is caused by the inverted typhoon trough, subtropical high and westerly trough; the different locations of subtropical high bring about the difference between positions of southeast jet surrounding these two typhoons, and the southeast jet surrounding Prapiroon is more favorable to the maintenance of squall line. In the initial stage, abundant vapor source, distinct convective instability, accumulation of instable energy and decrease of convective inhibition provide beneficial conditions, and the scattered convective cells are organized into squall lines by the surface convergence line; the different vapor conditions and locations of surface convergence line lead to different positions of two squall lines initially; potential instability of conditional unstable air layer, CAPE (convective available potential energy) and CIN (convective inhibition) indicate the convective development potential of squall line Prapiroon is more intense than the squall line Rammasun. The temperature characteristics of squall line preceding Prapiroon is more evident than that of Rammasun; vertical dynamic structure benefits the generation and development of severe convection; compared with previous research on westerly squall lines, thunderstorm high and positive variation of pressure are not found in these two squall line processes, but cold pool, distinct temperature gradient and pressure gradient have been detected, and vertical wind shear in the bottom layer relies mainly on the wind vector difference. When the bottom of westerly trough and the top of inverted typhoon trough are combined in the north of Hunan Province, convective cells strengthen and form the squall line of later stage. Compared with previous westerly squall line, during the two squall line processes, strong thunderstorm high pressure and positive pressure are not fingered out instead of cold pool, obvious temperature gradient and pressure gradient, and the lower vertical wind shear is given by the wind vector difference.