关键词: 大降水, 大气环流, 分型

Abstract:

Based on observational data of Hami ( eastern of Xinjiang)and NCEP reanalysis data，the atmospheric circulation features　which could cause large precipitation (greater than 12.0 mm)in Hami were analyzed． Results show that there were four kinds of synoptic patterns which could cause large precipitation in Hami，including the transverse‐trough‐type，low‐vorticity‐type，low －trough‐type(or ω‐type)and unstable‐small‐trough‐type．The cases of torrential rains (24 hours rainfall more than 24.0 mm)were mainly concentrated in the low‐trough‐type ( or ω ‐type) ，and the precipitation of the cases for transverse‐trough‐type was between 13.0‐22.0 mm，and it was between 15.0‐20.0 mm for the cases of low‐vorticity‐type，while it was less than 18.0 mm for cases of unstable‐small‐trough‐type．Four types atmospheric circulation characteristics were significantly different mainly in middle and upper troposphere．The circulation was straight in the middle and low level for transverse‐trough‐type，the north of the transverse trough was northwest airflow，and the south Asia high pressure was lying over the west of Qinghai‐Tibet Plateau．There was a trough over Bay of Bengal and a low vorticity in the north of the trough，the ridge in the west of low vorticity was strong，and the south Asian high was lying over the eastern of the Qinghai‐Tibet Plateau． The ridge in east of the trough was stranger and lay northwest to southeast in the cases of low‐trough‐type ( or ω ‐type) ， and the south Asian high was the Iran‐High‐type．As to unstable －small‐trough‐type，the south Asian high presented a band from Iranian plateau to the eastern Tibetan Plateau，and a straight westerly flow was over the west of 85°E，while a small shortwave trough lay over the eastern region of Xinjiang．

Key words:  large precipitation, atmospheric circulation, classification