Based on Doppler Radar products and observation data in Shaanxi from 2012 to 2016, the standard for the backward-propagating thunderstorm survey in Shaanxi was established.The temporal and spatial distribution characteristics of 48 backward-propagating thunderstorm processes in 5 years were statistically analyzed.It indicates that backward-propagating thunderstorms tend to emerge between 14:00 and 18:00 (Beijing Time) from June to August in area of Shanbei and northern Guanzhong.The disasters are mainly short-term heavy rainfall.The new echo survives 1 to 2 hours, while its center can develop to be the strongest at 10 to 30 minutes.According to the moving direction, the new echo pattern can be categorized into three types: Forward-propagation along advection (type 1), continuous backward propagation (type 2) and low movement (type 3).Typical processes are selected for analysis.The results show that type 1 thunderstorm occurs in the unstable environment of upper-level cold vortex and lower-level shear line, which is triggered by coordination of ground convergence line and the dew point front.The convective movement develops along the convergence line and the dew-point front, and eastward advection develops reversely, which forces the thunderstorm propagates backwards.After regeneration, the strong environmental wind and the weak vertical wind shear cause the thunderstorm to move forward with the advection.The propagation of type 2 thunderstorm is closely related to the movement of gust front.The gust front in the front of cold pool on the ground forces warm moist air to ascend near the ground convergence line to generate a new thunderstorm.The thunderstorm propagates along the intersection of the moving gust front and the ground convergence line.Type 3 thunderstorm occurs where the upper-level trough leans forwards.In this structure, the ground convergence line and the significant dew point front trigger the generation of a storm cell, and the strong vertical wind shear strengthens its maintenance.The storm tends to move towards the unstable layer on the northwest side of the dew-point front, which shows characteristics of backward propagation.However, this self-propagation is offset by eastward advection, resulting in stable and low movement.
Qiyuan HU
,
Nan WANG
,
Pingyun LI
,
Jing YUE
. A Preliminary Study on Statistical Characteristics and Mechanism of Backward-Propagating Thunderstorms in Shaanxi[J]. Plateau Meteorology, 2020
, 39(5)
: 973
-985
.
DOI: 10.7522/j.issn.1000-0534.2019.00099
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