Plateau Meteorology

Plateau Meteorology >

2018 , Vol. 37 >Issue 5: 1277 - 1288

DOI: https://doi.org/10.7522/j.issn.1000-0534.2017.00070

Causation Analysis of a Short-Time Strong Rainfall Triggered by Cold Front at the Northern Piedmont of Qinling Mountains

  • WANG Nan ,
  • ZHAO Qiang ,
  • JING Yu ,
  • ZHANG Xiaowen
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  • Shaanxi Meteorological Observatory, Xi'an 710014, shaanxi, China;National Meteorological Centre, Beijing 100081, China

Received date: 2017-06-21

  Online published: 2018-10-28

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Abstract

On August 3, 2015, a short time heavy rainfall suddenly occurred at the northern piedmont of Qinling Mountains, whose intensity has been rarely seen in recent years, triggered floods and caused casualties.Based on the analysis of aerological sounding data, intense surface observation data, NCEP reanalysis data, wind profile data and Doppler radar data, it was found that the precipitation process has good convective potential and humidity condition, and it was triggered by the cold front system.The structural features of the cold front system include:thewater vapor content was greater than 18 g·kg-1 near surface in front of the front zone, the frontal rising motion located above the sinking movement and below the free convection level, there was significant convection instability ahead of the front and so on, which are all favorable conditions for the occurrence of convective strong precipitation.The calculation result of frontogenetical function showed that strong frontogenesis(up to 20×10-10 K·s-1·m-1) of this process mainly occured in the middle and lower troposphere.The main reason is that the cold front system was accompanied by strong cold advection at 850 hPa which caused the horizontal frontogenesis; convective instability and the ascending motion caused vertical frontogenesis.In addition, the strong cold advection at 850 hPa caused shallow temperature inversion of the layer, so that convective instability energy can be concentrated, that is another favorable factor for the development of strong convection in the afternoon.The wind shifted to the west and formed ultra low level strong westerly wind with feedback of heavy rainfall after the cold front passed due to the blockage of Qinling Mountains.The westerly winds combining with the windward slope of Qinling Mountains made amplitude effect to the precipitation and brought low level water vapour transportation for the precipitation area, but the presence of the ultra low westerly wind causes the environment wind appeared negative vertical wind shear and was consistent with the moving direction of the storm.Under the influence of such wind field, the bottom of the storm which has just been established moving eastward faster than the top, and the vertical structure of the storm is difficult to maintain for a long time.The wind profile radar can detect the fine vertical wind structure of the cold front system, which reflects the vertical structure information of the cold front and predict weather system development much earlier than the other meteorological elements, which has a good indicative significance for the forecast.

Key words： Frontogenesis; short-time heavy rai; wind profile radar; ultra-low-level west

Cite this article

WANG Nan , ZHAO Qiang , JING Yu , ZHANG Xiaowen . Causation Analysis of a Short-Time Strong Rainfall Triggered by Cold Front at the Northern Piedmont of Qinling Mountains[J]. Plateau Meteorology, 2018 , 37(5) : 1277 -1288 . DOI: 10.7522/j.issn.1000-0534.2017.00070

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