| Rainstorm is one of the primary disastrous weather in China. It has significant importance to predict rainstorm precisely and timely, which can greatly reduce its damage. This paper analyzes a heavy rainstorm process that occurred in Taiyuan Region, the south-central part of Shanxi province, during 15th～17th August 2005. The analysis is based on NCEP 1°×1°global grid point data, MICAPS ground and air data offered by China Weather Bureau, T213 objective analysis data and the cloud picture data of FY-2C satellite. Furthermore, this paper diagnoses and studies the data simulated by MM5 meso-scale model and gets the following results:(1) Under the weather background of Europe-Asia middle and higher latitudes being two ridge one trough meridional circumfluence, cold air moved towards east and south, which made West Pacific subtropical high weaken and withdrew to south and east. This rainstorm process was resulted by the influence of 500hPa cold low trough, middle and low layer shear line, West Pacific subtropical high, ground cold front and other weather scale system.(2) Before the rainstorm occurred, unstable energy and abundant water vapor accumulation of the air above Taiyuan prepared the ground for the occurrence of the rainstorm; During the process, the transportation of the middle and low layer leaning south air current to water vapor and energy and the convergence climbing movement of low layer water vapor was of great benefit to the production and maintenance of the rainstorm; The strong precipitation during the rainstorm process was just occurred in the atmosphere "up-dry-down-wet" convection unstable region, and low layer high energy tongue leaned to the energy front side.(3) The good configuration of vorticity, divergence and vertical velocity resulted in the strong climbing movement of fargoing strong air current below 200hPa, it also provided dynamical condition for the production of the rainstorm; Meso-βconvergence line provided advantageous trigger condition for strong precipitation.(4) The space time distributing of the rainstorm was quite asymmetric. The precipitation mostly presented to the east of Taiyuan. The strong precipitation focused on 5-11 am. on August 16. And it was caused by 2 Meso-βrain group movement which created from southwest of Taiyuan and became more stronger during the movement to northeast. Because the rain group appeared repeatedly on very small area during very short time, the great rainstorm came into being in center city, heavy flood damage was formed.(5) Weather satellites can provide abundant detection data of high space time resolution. Tracking and analyzing the data can help us catching characteristic information of meso-and-small-scale system earlier and accurately. Therefore it can make up the shortage of analyzing conventional data and numerical mode production, gain time for short-time warning in advance for the rainstorm and other disaster weather, and furthest alleviate losing.MM5 meso-scale model successfully simulated the precipitation process, which indicated that:(1) The distribution ofθse field showed that unstable energy of low latitude was delivered northward continuously under the effect of the leaning south air current, which made new unstable energy supplied to the air near shear line, kept the strong convection and the strong precipitation weather.(2) The section structure of divergence field primely reflected four phases of the foundation, development, flourishing and vanishment of low altitude convergence and high altitude divergence. During the occurrence process of strong precipitation, the rainfall region maintained the structure of the low altitude convergence and high altitude divergence all along. It indicated that the distribution of divergence field and the occurrence time of the strong precipitation had satisfactory corresponding relations.(3) The raising altitude and intensity of vertical motion had good fitting relations with precipitation intensity. The maintenance of strong raising motion resulted in the persistence of the precipitation.(4) 700hPa isobaric surface potential vorticity can be corresponded well with precipitation intensity and predicted area. Strong precipitation was always laid the east of potential vorticity center where the value of potential vorticity was small, and the stronger the value of potential vorticity center, the stronger of corresponding precipitation. It showed that potential vorticity had good indication meaning to the precipitation intensity and predicted area. So it was an important physical quantity of rainstorm diagnosis.(5) To the rainstorm, spiral value is a parameter of strong relativity. The rainstorm occurred in the area where the spiral value is as big as 600~700hPa. The max. of the rainstorm appeared at about 4 hours later after the appearance of the spiral value extremum. And the increase or decrease of the positive center intensity of spiral value has a meaningful indication to the appearance and the end of precipitation.
|
PDF Full Text Request