| Short-duration heavy rainfall(SDHR)forecasting is important and difficult in severe convective weather forecasting, for its characteristics that being sudden, short duration, dispersed in location and hazardous. Especially in Gansu, the arid and semi-arid area, a severer disaster could be brought about by SDHR. This paper analyzed the temporal and spatial distribution of SDHR in recent 11 years occurred in Gansu Province with statistical methods. Moreover, the differential characteristics were investigated with the diagnostic analysis method, by comparing the baroclinic frontogenes convective weather and the strong convection weather forced by low level warm advection, which occurred in the same season and similar climate.Based on the hourly precipitation data from 81 stations in Gansu province from2002 to 2012, the characteristics of SDHR were discussed from the spatial and temporal variation.The results showed that: in Gansu Province, SDHR mainly dispersed in Hedong area of Gansu, the number of days with SDHR gradually increased from the northwest to the southeast, SDHR were the most intensive in the southeast of Gansu. There were two high centers, one of which in eastern Gansu region with the center of Heshui,another in Huicheng basin with the center of Hui xian. SDHR occurred from May to September, and mostly from July to August, followed by June, May and September.Precipitation which is heavier than 30mm/h also occurred in May, and resulted in hazards, because of the abruptly and early occurring and then uneasy to forecast, even though in low frequency. The interannual variation showed that the frequency of SDHR increased from 2002 to 2012, and with peaks in 2006 and2010. SDHR occurred most frequently in 2010, up to 52 times, and happened only 17 times in 2004.SDHR mainly occurred during the night, especially in the early night, concentrated in the period between 16:00 to 00:00,with high-incidence time around 18:00.Precipitation with more than 50 mm/h easily occurred around 21:00, which should be noticed.SDHR occurred in Gansu from2004 to2014, were divided into two groups of the baroclinic frontogenes convective weather and the strong convection weather forced by low level warm advection. SDHR in the strong convection weather forced by low level warm advection precipitated more, usually occurred in July and August,with the characteristics that being intensive, regional, long-time duration. On the other hand, SDHR in the baroclinic frontogenes convective weather precipitated less,mainly in May and June, with the characteristics that being intensive, regional,short-time duration, dispersed, often with hail, lighting storm, gale and soon, and even reach rainstorm in some areas.Two typical cases of SDHR which occurred in the same season and similar climate were analyzed, namely the strong convection weather forced by low level warm advection(June 19 th in 2013)and the baroclinic frontogenes convective weather(June 18 th in 2014).The results showed that:(1)Baroclinic frontogenesis heavy rainfall is the intense interaction between cold and warm air in the lower level,which accompanied with significant temperature in the lower intersection of cold and warm advection strong and obvious frontogenesis, the ground cold front. The cold and warm advection cause baroclinic frontogenesis, convergence and uplift of the formation of such coercion is an important condition for the occurrence of SDHR. The warm advection forced heavy rainfall in the lower is mainly controlled by the warm advection areas,the warm and moist advection played a leading role in the establishment of thermal in stability, no obvious frontogenesis phenomenon.(2)The instability of baroclinic frontogenesis heavy rainfall is greater than the warm advection forced heavy rainfall. And there is a convection inhibitory energy,conducive to the development of severe convection weather. The wet layer thickness of warm advection forced heavy rainfall is higher than baroclinic frontogenesis heavy rainfall. The baroclinic frontogenesis heavy rainfall behaves more vertical wind shear.Two types of heavy rainfall are positive vorticity and vertical ascent motion.(3) The cloud characteristic of warm advection forced heavy rainfall is the rapid development strip cloud to the north. But the cloud characteristic of baroclinic frontogenesis heavy rainfall is manifested with the comma cloud corresponding with the herringbone shear of the low level. Developments and changes of the cloud is closely related to the development and changes of the precipitation area.(4) The radar characteristic of warm advection forced heavy rainfall is the mixed precipitation echo mainly of cumuliform cloud. The small gradient of echo,low center of mass,which called the warm cloud precipitation. But the radar characteristic of baroclinic frontogenesis heavy rainfall is the bulk convective echo dispersed in the layered cloud. The large gradient of the echo large, high echo centroid development, can develop into a echo intensity.In practical of weather forecasting, we can confirm the basic configuration by analyzing the large-scale circulation, and judge the weather phenomena and precipitation characteristics which might occur in a short time. Then basing on three basic conditions of the formation of strong convection, we can analyze the multiple physical characteristics to confirm the development of weather systems, as well as the precipitation area and intensity. |
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