Analysis On A Remote Typhoon Rainstorm Process During The Meiyu Period

In this work, the analysis on the rainstorm process during the late Meiyu period of2011in Nanjing city of Jiangsu province is performed with NCEP1°×1°reanalyzed data, ground station and sounding data of MICAPS system, precipitation data from TRMM satellite, rainfall data from Automatic Weather Stations, Doppler radar data from Nanjing and Changzhou baseline station and data from multi-functional transport satellite-2of Japan, from the rainstorm weather process and the synoptic background and basic conditions which rainstorm occurred in. on this basis, Simulation and sensitivity experiment about removing typhoon was carried out to the rainstorm process by the mesoscale model, which revealed the influence of typhoon on the rainstorm process. The main results are as following:The precipitation between0000BST18July and0000BST19July in Nanjing area was south-north and was mainly concentrated within three periods. The precipitation in the first two periods was caused by the isolated convection cells and the torrential rainfall in the third period was caused by three mesoscale convective systems, which are in the north of Nanjing, near Nanjing and in the southwest of Nanjing. These convective systems merged successively and lasted long time near Nanjing area and leads to heavy precipitation in Nanjing.In this case, the heavy rainfall occurred ahead of a deep trough in the mid-upper troposphere, near the low-level shear line, and in the northeast of the surface depression. It was caused by the combined effect of the mid-latitude low system and the accompanied low vortex in low layer and typhoon "Ma-on" which was moving northwest. In the southeast coastal areas of China, the southeast-to-easterly flow located in the northeast of the low vortex at925hPa transported water vapor which came from the West Pacific to the heavy rainfall area continuously, which provided favorable moisture conditions for the occurrence of the heavy rainfall. Not only that, this southeast-to-easterly flow also made warm advection obvious in the south china and the southeast coastal areas. The slight warming induced by the warm advection in the low troposphere and the thickening of humidity layer resulted from the water vapor transportation led to instability near Nanjing, which was beneficial to the heavy rainfall occurrence. Along with the northwest movement of Ma-on, the dry air in the subtropical high on its north side was gradually advected to the southeast coastal areas of China. As a result, an energy front developed between the dry air and the warm moist flow on the mainland. Meanwhile, in the middle reaches of the Yangtze River area, the remnants of Meiyu front also manifested as an energy front. Two energy fronts intersected near Nanjing, and gave rise to the apparent ascending motion there. It is the upward motion that triggered the heavy rainfall in Nanjing area.