| Rainstorm is a common disastrous precipitation event,for it can usually reaulted in disasters such as flash,dike breaching,landslides and debris flow floods in summer.Yet,the formation mechanism and evolution of extreme rainstorm in North China where rainstorm disasters often happened was not known clearly.So there is an urgent need to strengthen the scientific research on the extreme rainstorm in North China.For the extremely heavy rainfall case occurring between 18 and 21 July 2016 in North China,precipitation characteristics firstly was fully recognized.On the basis,Interaction of multiple scale weather systems was examined and based on some dynamical parameters,a diagnostic analysis and forecasting study of this torrential rain event were carried out.The torrential rainfall event was carried simulated by using the Weather Research Forecast modeling system.The effects of microp hysics schemes,divided into two groups of nine single and seven double-moment schemes on rain fall area and intensity of precipitation were evaluated.The main results were as follows:(1)The amount of precipitation in the extremely heavy rainfall was the largest next to in that between 2 and 8 August 1963 in North China.For the slow-moving rain band,the strong rainstorm last more than three days.During the rainstorm,accumulative precipitation in most parts of North China was recorded greater than 100 mm with the maximum precipitation of 783.5mm.The Zonal heavy rainfall area was located in the western and nothern edge of the North China Plain and topography promoted precipitation increment.There were two strong rain centers in North China.The first one was located in Taihang Mountains and presented convective precipitation.The second one was located in south-central part of Beijing and presents stratiform precipitation.(2)The extremely heavy rainfall occurred under typical weather patterns with high pressure to the east and low pressure to the west.The overlapping of the east moving and growing westerly trough and east-north moving southwest vortex formed the North China cyclone.So there was a deep and moving slowly low-pressure system over North China as Subtropical high pressure moved to the west and lifts to the north,and came into being high pressure barrier together with high pressure ridge in northeast China together.There was the coupling of jets at the upper and lower levels from the northeast side of low-pressure system.And the abundant vapor with transferred by low-level jet stream was uplifted of the cyclonic circulation convergence.The east-north moving southwest vortex played a key role in the extreme heavy rainfall.Plantcau vortex from Upper troposphere enhances the baroclinity of vortex,which was conducive to vortex of low level.However,Importance role of latent heat of condensation should be taken into account.(3)There were two stages during the extremely heavy rainfall according to differences of synoptic situation.When the rainfall occurred in warm areas of upper trough,there was baroclinic instability develop in cyclone with cold air invasion,terrain of Taihang Mountains,and easterly wind in the prefrontal area.When rainfall occurred with low vortex(cyclone).Warm cloud precipitation was obviously in northern of North China.Under favorable synoptic circulations,the frequent development of stable and persistent MCS was important for the formation of the heavy rainfall event examined in this study.(4)When rainfall occurred in warm areas of upper trough,the moist thermodynamic advection parameter corresponded to the observed precipitation very well but When rainfall occurred with low vortex(cyclone),generalized moist potential vorticity and the second-order potential vorticity played an equivalent role.The divergence flux and vertical helicity,particularly thermal vertical helicity and thermal vertical divergence flux,could more accurately trace the heavy rainfall region.THP corresponded to the observed precipitation in two stages of rainfall.But when rainfall occurred in warm areas of upper trough value of THP is lower than when rainfall occurred with low vortex(cyclone).(5)As a rather good reproduction of rainfall,as time goes on,differences between schemes was more obvious.The results of the double-moment schemes present less simulation effect,com-pared to the results of the single-moment schemes in terms of rain mixing ratio,solid hydrometeor and vertical velocity.The double-moment schemes were much better than its contrary one.Overall,it was the SBU_YL in that provided the most successful simulation scheme on torrential,and the simulation of rainfall area and intensity of the rainfall agreed well with observations.In view of this,this study contributes to a deeper understanding of the formation mechanism and evolution of extreme rainstorm in North China,it can also provide some references for the research of the extreme precipitation.What's more,it is of great practical significance and scientific value to improve the accuracy of rainstorm prediction,early warning of extreme rainstorm in North China,which can ensure safety of life and property of the people. |
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