| The flash heavy rain is a severe convective weather with high frequency in warm season.Jiangxi Province is located in the south of the Yangtze River.The flash heavy rain occurs frequently in warm season,resulting in serious flood and waterlogging disasters.In addition,it is difficult to forecast because of the dense hills and rivers and lakes,complex topography in Jiangxi Province.This paper starts from the statistical characteristics of flash heavy rain in warm season in Jiangxi Province,and then builds the conceptual model of sensitive physical quantities and weather situation related to flash heavy rain.Finally,WRF mesoscale numerical model is used to study the effect of Poyang Lake on flash heavy rain.The results can be used as reference for flash heavy rain forecast in Jiangxi Province.The main conclusions are as follows:(1)The total rainfall of flash heavy rain in Jiangxi Province has the phenomenon of uniform more or less rain in the whole region,and there is also the difference between the north,south and the Poyang Lake plain.The high frequency area of flash heavy rain are mainly distributed in Mountainous areas and near river valleys.They are the eastern side of the Luoxiao Mountain,the western foot of Wuyi Mountain,the Xinjiang,the Lean and the Changjiang river valleys.The frequency of flash heavy rain near the river valley is the highest in the Changjiang river valley(16.9 times one year),the highest near the Mountains is the east side of the Luoxiao Mountain(12.6 times one year).The extreme flash heavy rain are located in the Mountain area of northeast Shangrao(3.7 times one year)and the Jinjiang river valley(3.3 times one year).Flash heavy rain mainly occurred in the 3rd hou of May,middle of June and July,and from 2nd to 3rd hou of August.The diurnal variation characteristics of region ? and ? are single peak type,diurnal variation characteristics of regions ?,? and ? with bimodal patterns.The main peaks are concentrated at 17 o'clock in the afternoon;the second peak is at 08—10 o'clock in the morning.(2)The average of flash heavy rain in Jiangxi Province is about 5 times in the warm season,most of which are mainly 20~30 mm? ?-1,The contribution rate of flash heavy rain to rainstorm is basically above 40%.The Xinjiang river valley is the center of rainstorm rainfall,while it is not the center of flash heavy rain rainfall.But the Changjiang river valley and the western foot of Wuyi Mountain are both the center of rainstorm and the center of flash heavy rain rainfall.(3)Flash heavy rain is maintained within 1 hour,and 2 hours is less than 10%.The flash heavy rain with duration of 3 hours or more mainly concentrated in the southern side of Poyang Lake.The narrow tube zone composed of Lushan Mountain and it's western side of the Mountain,the Mengshan leeward slope of Xinyu City,the windward slope of Huangshan Copulse at the border of Jiangxi and Anhui provinces,the Changjiang river valleys,the southwest side of Poyang Lake,the north part of Fuzhou City,Jinggang Mountain,western Ganzhou City,these areas are prone to trigger flash heavy rain gtater than 40 mm one hour and duration more than 2 hours.Even Changjiang valley area can reach the extreme flash heavy rain for 6 hours and the heavy rain weather for 3 days.(4)There are five main weather patterns affecting the flash heavy rain in Jiangxi: cold front type,southwest jet type,the subtropical high type,warm shear type and typhoon type,each type accounts for 31%,41%,9%,12% and 8%.The flash heavy rain of cold front type,southwest jet type and warm shear type appeared in May and June,the subtropical high type mainly occurred in July,the typhoon type occurred in July to September,but most of them were concentrated in August.(5)The characteristics of environmental parameters are: The CAPE of cold front type,subtropical high type and typhoon type is larger,average is 1200 J/kg,the southwest jet type and warm shear type are concentrated between 500 and 1200 J/kg.Cin is basically between 20 J/kg and 60 J/kg.The K index of the typhoon type is higher than 38 ?,and the other four categories reach 32 ?.The S index is basically less than-1.1?.The lowest of the southwest jet type and the warm shear type is 21 ?,the second is the cold front type(the threshold is 22?),the typhoon type is 24?.About 70% of T700-T500 is above 13?,and 75% of T850-T500 is above 23?.In regard to 850 h Pa ?se the cold front type and southwest jet type greater then 340 K can be obtained,the other three types need to be more than 345 K.Most of the PW is above 50 mm,the maximum is typhoon type,the average PW is 70 mm,the second is the cold front type,average is 63.7 mm,the average height of the sub high edge type and the warm shear type is about 61 mm,the threshold value is about 50 mm,the southwest jet type is the lowest,the average is less than 60 mm.(6)The cold front type,southwest jet type and warm shear type is controlled by the 588 line on the 500 h Pa and the subtropical high located the South China Sea.The subtropical ridge line is located near 15°N and is stable with little movement.850 h Pa warm and wet airflow from the Bay of Bengal is steadily transported to Jiangxi area.Precipitation is mainly concentrated in the Poyang Lake Plain.The 588 line of the subtropical high type in 500 h Pa controls much of South China,lifting northward to the south of Jiangxi Province.The subtropical ridge line is located near 20°N and is stable with little movement.850 h Pa has warm and wet airflow from the Bay of Bengal,and at this time the low layer to the near surface is high temperature for a long time.At the same time,the stratification instability develops violently in summer afternoon,and precipitation is mainly concentrated in the middle and east of Jiangxi Province at the edge of the subtropical high,which leads to atmospheric instability due to the increase of the temperature difference between the lower and middle layers of the atmosphere and the accumulation of a large amount of energy at the same time.Typhoons often occur from August to September.Typhoon landings in Guangdong or Fujian will affect the flash heavy rain in the south and northeast of Jiangxi Province.The precipitation is mainly concentrated on the north or west side of the typhoon.(7)According to the comparative experiment of lake or not,the precipitation process in area A is reduced by about 10%.The influence range on humidity is less than temperature,the temperature field can be reduced roughly in the vertical direction of 500 m and horizontally in the range of 100 km,and the sensible heat,latent heat flux field can be reduced by about 50% in the horizontal range of 100 km.At the same time,Poyang Lake can provide continuous water vapor transport for the nearby area,but the thermodynamic effect of the lake is stronger than that of water vapor,so that the precipitation near Poyang Lake can be reduced. |
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