The Analysis And Forecasting Research Of Short-duration Rainstorm In Wuhan

Short duration rainstorm is a weather phenomenon,common in the summer of Hubei province.It may have strong distory,and easy to cause significant economic losses..Wuhan City in Hubei Province as the economic, cultural, and political center, short duration rainstorm brought the city waterlogging, which resulting in a greater impact on the public transportation, and a high degree of social concern. In this paper, Short-duration Rainstorm were analyzed by the1961-2011annual rainfall recording observation data, NECP1°×1°gridded data, infrared satellite data. Short duration rainstorm have been divided four type,such as::shear vortex warm eastward type (Ⅰ), the northern trench cold shear type (Ⅱ), the South inverted trough (Ⅲ) and double vortex type (Ⅳ). MCS and the weather systems,as well as the main feature of water vapor momentum, and energy stability, were studied through the actual one case analysis, and the causes four types of short duration rainstorm and forecast point were revealed, its main forecast index was discussed and tested in2013.the main result that:(1) Interannual variation of short-duration rainstorm is larger,1hours more than30mm is current in a rich period, but3hours more than50mm is in the short period time. short duration rainfall evens occur most frequently in July and June. similar to heavy rainfall distribution; January-March, October-December of every year has no short duration rainstorm. it appears most in the19:00, but at least appear in13:00.(2) In addition to the Ⅱ class of Wuhan, short duration rainstorm mostly by vortex or low value directly affect the system, accounting for more than83%. In addition to Ⅲ, there are the southwest low jet impact a wind speed exceeding12m/s Wuhan short duration rainstorm, the analysis of satellite images show, warm shear at the southwest low jet vortex in front of the left or the Northeast easy generation of mesoscale convective cloud cluster, the shear, the wind speed convergence or the cyclonic convergence effect, the development of strong convective clouds, caused by the occurrence of short duration storm.(3) Thermodynamic conditions and convective instability condition analysis showed, Wuhan mean K index at36℃or above, convective available potential energy is generally in the600～800J/Kg. Theta se over345K. Convective instability conditions of0se (850hPa-700hPa) Wuhan mostly in more than5K, the Ⅰ class for3K.(4) The water vapor condition analysis showed, except Ⅲ, Wuhan were located in the wet tongue. Above monolayer mean specific humidity in Wuhan14g/Kg, single average dew point Wuhan4deg..3layer specific humidity and more than38g/Kg,4layer of dew point and more than34℃. On the vertical distribution of the wet layer thickness, high humidity,500hPa above4g/Kg.(5) The I class of short duration storm the main mechanism lies in the eastern Sichuan Basin and Chongqing plateau vortex, vortex carries positive vorticity along the warm shear to the east of Hubei, the Northeast Vortex warm cutting point strong ascending motion and promoted the development of the mesoscale convective clusters, is the main cause of Wuhan short duration rainstorm. The main point of forecast:500hPa on the plateau to the east of volatility continue eastward, middle layer in the eastern plateau to Sichuan, Chongqing and small vortex vortex development division east out of. The development of mesoscale convective cloud near the Wuhan, lasted more than3hours. Warm tongue to the eastward expansion, Hubei senior (500hPa,700hPa) east west cold warm. Significantly decreased925hPa and500hPa specific humidity, indicates the strong precipitation will be weakened.(6) The Ⅱ class of short duration storm the main mechanism lies in the westerly trough deep carry a strong cold air and the subtropical high peripheral southwest warm wet air current intersection produce strong ascending motion frontal cloud system, wind convergence at low level cold frontal cloud system Shear strong, mesoscale convective cloud cluster strengthen in Wuhan., resulting in short duration rainstorm. The main point of forecast:westerly trough deep grooves, northwest air carries the strong cold air southward. The subtropical high control department of Southern China was East belt. Wuhan is located in front of the warm ridge trough. Warm ridge towards the extension from the south to the north. Significantly decreased925hPa and500hPa specific humidity, indicates the strong precipitation will be weakened.(7) The III class of short duration storm the main mechanism lies in the tropical low value system through Southern China into the land, the periphery of easterly waves or low value system in high moisture flow influenced by the uplift of the cyclonic circulation convergence and the westerly trough or special terrain, resulting in short duration rainstorm. The main types of forecast point:tropical low value system or easterly wave in high humidity air strengthen convergence in inverted shear at. The westerly trough and trough with. The Western Pacific subtropical high is located in East China coast or subject.(8)The IV class of short duration storm the main mechanism lies in the eastern plateau low value system to the southeast from the low trough in the vicinity of Guizhou, and Guizhou in the vicinity of a vortex generating eastward, along the West Pacific subtropical high peripheral to the northeast from the southwest airflow, split, forming double vortex circulation. Vortex to move to the northeast of the Jianghan Plain, northeast of strong convergence, resulting in Wuhan short duration rainstorm. The main point of forecast is:westerly trough system, the Yunnan Guizhou trough are obvious, the subtropical high is located on the southeast coast, a vortex along the subtropical high peripheral flow northeast to move to Hubei in the East, southern Henan. Warm and humid air comes(9)According to the characteristics of the circulation configuration and elements of four short duration rainstorm combined with case analysis, summarizes the prediction index. In20136times forecast test shows,1hour rainfall close to30mm/h of trough type rainstorm is easy to false alarm and missing.