Characteristics of Warm-Sector Rainstorms in Southern Hunan Province from 2012 to 2021

ZHOU Yiqing; SONG Nan; ZHOU Changqing; TANG Minghui; YUAN Tao

doi:10.16032/j.issn.1004-4965.2024.038

Abstract：By using conventional observational data and NCEP reanalysis data,the present study analyzed the temporal and spatial distribution characteristics of 66 warm-sector rainstorm(WR)cases in southern Hunan province from March to September between 2012 and 2021.These cases were categorized into three distinct types based on synoptic situation:warm sector in front of cold front(CF)type,southerly wind(SW)type,and warm shear(WS)type.Synoptic conceptual models were established for each type,and the physical parameters leading to these storms were explored.The results show that:(1)The annual variability of WRs in southern Hunan exhibited an undulating upward trend,with daily peaks occurring between 19:00 and 22:00.The storms were most extensive in May,most frequent in June with the highest maximum daily rainfall,and more localized from July to September.(2)The SW type was the most frequent with the highest maximum daily rainfall,followed by the WS type,while the CF type was the least common,with each type peaking in different months:April to June for the CF type,May to August for the SW type,and June to July for the WS type.(3)The diurnal variation of short-duration strong rainfall(hourly rainfall≥20 mm)of the CF type and the WS type was intense,while that of the SW type was slightly gentle.(4)The high-frequency area for WRs was closely related to the terrain distribution of the Nanling Mountains,Luoxiao Mountains,and Yangming Mountains;the Dongjiang Lake also contributed to increased precipitation.The CF type was more likely to occur at trumpet-shaped topography in the southwest;the WS type was concentrated on the windward slope of the Nanling Mountains and near different underlying surfaces,while the SW type's occurrence was more dispersed.(5)The main influencing systems included upper-level troughs,low-level and ultra-low-level jet streams,surface inverted troughs,and convergence lines.Moreover,the 200 hPa divergence zone,the 850 hPa warm high ridge,the significantly humid region,and the topographic effect contributed to increased precipitation.(6)The jet streams at 700 hPa,850 hPa,and 925 hPa played important roles in the water vapor transport of the CF type,the WS type,and the SW type rainstorms,respectively.(7)The average values of physical parameters before WRs were as follows:specific humidity of 850 hPa≥13 g·kg-1,CAPE≥1 100 J·kg-1,K-index≥37℃,Showalter index≤-1.5,temperature difference between 850 hPa and 500 hPa≥23℃,lifting condensation level between 0.6 and 0.9 km,0℃ isotherm height between 4.9 and 5.1 km,and 0-6 km vertical wind shear between 10 m·s-1 and 16 m·s-1.