Analytical and numerical studies of a quasi-stationary precipitation band observed over the Kanto area associated with Typhoon 9426 (Orchid)

Abstract

A quasi-stationary precipitation band, which persisted for more than 10 hours, was observed along a mesoscale front over the Kanto area, when Typhoon 9426 (Orchid) approached the Japan Islands. The band was analyzed using data of special upper sounding at Tsukuba, two Doppler radars, and operational meteorological observations. The band had the carrot-shaped form and characteristic features of the back-building type. In the precipitation band, which aligned from south to north, a multi-cellular structure was observed. New cells were repeal edly generated at the southern edge of the band, and moved northward, expanding westward. Numerical simulations with the horizontal resolution of 2 km were performed using the Meteorological Research Institute mesoscale non-hydrostatic anelasuc model. The characteristic features of a quasi-stationary precipitation band was well simulated, although a mesoscale front was generated about 100 km southeast of the observed position. This lasted for more than 3 hours, and reproduced features of the back-building type. In the simulated band, the carrot-shaped form is produced by the northwestward movements of the cells, and the enhancement of the cells on the eastern flank of the band. By changing environmental fields and cloud microphysical processes, sensitivity experiments were conducted to investigate the formation mechanisms of the precipitation band. It was shown that the supply of high equivalent potential temperature air, from the upwind side of the middle level wind, and the vertical wind shear are essential.