Using conventional observation data, satellite cloud images, doppler radar data of Xi'an station and ECMWF reanalysis data (0.25°×0.25°), the convective environmental conditions and triggering mechanism of two short-term rainstorms which occurred in Xi'an on 2 and 3 August 2015, causing flash floods and mudslides and resulting in railway interruption and casualties were comparative analyzed.Results show that atmospheric environment conditions are obviously different.Xi'an is controlled by subtropical high, has high temperature and humidity and ground temperature reaches 39 ℃, CAPE value is more than 2000 J·kg-1.The decline rate of vertical temperature from ground to 850 hPa is close to superadiabatic state, which is very conducive to the triggering of convection on 2 August 2015.However, on 3 August 2015, Xi'an is located at the intersection of cold and warm air between the trough and subtropical high.There is a ground cold front moving southward in northern Shaanxi and air instability near surface layer decreases.Cold advection is stronger and ground temperature drops to 30 ℃, CAPE value is 800 J·kg-1.The synoptic scale system forcing is stronger on 3 August, although the temperature and unstable energy are significantly lower than those on 2 August.From the perspective of triggering mechanism, the surface convergence line triggers convection in the afternoon of 2 August in Yan'an and produces cold pool in the process of moving southward.The gust front of outflow triggers new convection, due to the large water vapor content and sufficient energy around Xi'an area, short-term rainstorm is generated and hourly precipitation is as high as 47.2 mm.However, the rainstorm in the afternoon of 3 August is triggered by cold front.Strong frontogenesis area corresponds well with the low-level cold advection area, which locates in the near-surface layer to 850 hPa.Diagnosis result indicated that vertical movement from ground to 850 hPa caused by frontogenesis secondary circulation makes the air mass overcome convective inhibition energy and rise to the level of free convection, which makes unstable energy release and produces heavy precipitation.During the process of cold front moving southward, due to the blocking effect of Qinling Mountains, a jet stream is formed in the boundary layer along the northern foot of Qinling Mountains.Strong thunderstorms continuously generated along the jet stream and train effect formed during the strom moving eastward, which causes heavy rain in the mountains.
Qiang ZHAO
,
Nan WANG
,
Xingxing GAO
,
Xiaoting CHEN
. Comparative Analysis of Convective Conditions and Triggering Mechanisms of Short-term Rainstorm in Xi'an on Two Consecutive Days[J]. Plateau Meteorology, 2021
, 40(4)
: 801
-814
.
DOI: 10.7522/j.issn.1000-0534.2020.00053
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