| As one of the warm season heavy rainfall centers in the Yangtze Huaihe River Basin,the Dabie Mountain has attracted much attention because of its complex terrain and the mechanism of precipitation by circulation interaction.Previous studies are mostly based on numerical simulation or case analysis,explaining the precipitation mechanism in the Dabie Mountains under certain weather conditions.In this paper,we hope to make a more objective analysis of the diurnal variation of precipitation in the different weather patterns in Dabie Mountains from a longer time series and a higher resolution grid data,and reveal the mechanism of the interaction between the topography and circulation in the Dabie Mountains.Therefore,in this paper,the 2008-2015,Jun.-Aug.0.10 × 0.1° CMORPH satellite-ground automatic station combined precipitation data,and the Hefei S band Doppler radar data are used in this study.The statistical characteristics of the diurnal variation of precipitation in the warm season in the Dabie Mountains are analyzed based on the oblique rotation T modal principal component analysis.And a case study is also carried out by a convective scale high resolution model named WRF_NJU.Firstly,the daily average 925hPa height field of the 2008-2015 06-08 is divided into 9 circulation patterns objectively.It is found that the precipitation contribution of the first 3 patterns to the warm season precipitation can be up to 70%in the Dabie Mountains.The first 3 types correspond to the southwesterly airflow(first type),the southeasterly airflow(second type)and the easterly airflow(third type)respectively.The space-time distribution characteristics of the Dabie Mountain precipitation under different circulation types are statistically analyzed by using the observation data with high temporal and spatial resolution.It is found that the precipitation,the frequency of precipitation and the intensity of precipitation are closely related to the circulation patterns:the first type is mainly the early morning heavy rainfall in the southwestern slop and the second type is mainly the early morning and afternoon precipitation in the southeastern slope,and in the third type,the precipitation in the Dabie Mountains is of high frequency and weak intensity in the afternoon though with a early morning second peak.In addition,it is found that the average precipitation intensity at peak time of the first pattern's early morning precipitation on the southeastern slope and the second pattern's early morning precipitation on the southeastern slope can reach about 4.5mm/h,while the average precipitation intensity at peak time of the third pattern's afternoon precipitation is only about 2.5mm/h.Secondly,to further study the early morning heavy rainfall on the southwestern slope of the first type,the difference of the daily average environmental field and its relationship with low altitude upstream wind speed in the no-morning precipitation type(153 days)and the typical morning precipitation type(28 days)in the southwest slope of Dabie Mountains are studied by using the 1°×1° FNL reanalysis data.The results show that when the 500hPa subtropical high is strengthened with a westward extension in Southern China,and the small trough of 700hPa is located on the north side of Dabie Mountains,and the 700hPa?850hPa low jet stream shows up on the southeastern side of Dabie Mountains,and the closed low vortex in the northwestern side of the Dabie Mountains,it is favorable for the early morning strong precipitation on the southwestern slope of the Dabie Mountains.Finally,by using the convective scale high resolution(4km)numerical model of Nanjing University,the early morning precipitation process occured on Jun.25th,2013 is selected as an example of the typical early morning strong precipitation of the first pattern on the southwestern slope.We reveal some main characteristics and the diurnal variation mechanism of precipitation on Dabie Mountains under the first circulation type by this case.The topography has two functions:one is to upraise the southwest jet and boundary layer jet stream comes from south of Dabie Mountains;the other is to block the northeast wind of the rainband in boundary layer so that the air pile stays in the north of Dabie Mountains can further lift up the airflow over mountains. |
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