Temporal and Spatial Distribution of Thunderstorm in Wuwei of Gansu Province

Thunderstorm is one of the most frequently disastrous weather in Wuwei of Gansu Province. The temporal and spatial distribution characteristics and changed trend of thunderstorm weather were analyzed by using the statistical methods based on thunderstorm data from 5 meteorological stations in Wuwei city during 1961- 2010,firstly. Combined the daily NCEP reanalysis data with 6 h temporal and 1° × 1° spatial resolution from April to October during 2001- 2010,the circulation pattern of thunderstorm weather were summarized through north- south airflow configuration. Results showed that the spatial distribution of thunderstorm weather in Wuwei was regionally obvious due to the altitude and topography,and the thunderstorm days in Tianzhu of southern mountain area was far more than those in other parts,which accounted for 40. 6% of the total thunderstorm days during 1961- 2010. The annual and decadal changes of thunderstorm days appeared declining tends on the whole,the declining trend in Tianzhu was most significant,and the climatic linear tendency was- 5. 819 d /10 a. The quasi- period of thunderstorm days in Wuwei was seven to eight years. The thunderstorm in Wuwei mainly occurred from June to August,which accounted for 70. 8% to 78. 6% of the annual total thunderstorm days.Additionally,the daily changes of thunderstorm weather in Wuwei were significant,mainly occurred from 12: 00 to 22: 00,especially from 13: 00 to 17: 00,and the average durations were 10 to 40 minutes. Regional characteristic of thunderstorm weather was very obvious,and the thunderstorm days reduced rapidly with the increase of thunderstorm station numbers. The circulation pattern of thunderstorm weather was divided into three categories in Wuwei city,i. e. northwest airflow,southwest airflow and westerly airflow types. To the thunderstorm with northwest airflow type,the cold advection on upper level was deep and slow- moving,which was beneficial to the occurrence of strong convective weather,the proportion of thunderstorm was the most. The cold air didn't remain after the weather system passed through Wuwei for the southwest airflow type,which wasn't conductive to the occurrence of strong convective,the proportion of thunderstorm was the least. The location of the upper vortex was to the north and the cold air was stronger for the westerly airflow type,which was more advantageous to strong convective weather occurrence,the proportion of thunderstorm was relatively higher.