ISSN 1006-9895

CN 11-1768/O4

An Analysis on Night Thunderstorm Weather over Beijing-Tianjin-Hebei Area during Mid-July 2015
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    Abstract:

    Thundershowers occurred every evening from 0000 UTC 15 July to 0000 UTC 19 July in Beijing-Tianjin-Hebei region. Results showed that the weather situation was different though the heavy rainstorm always occurred from evening to night. There was a "trough-ridge-trough" weather pattern at 500 hPa and Beijing-Tianjin-Hebei region was located in the unstable area in front of a trough from 15 July to 17 July. From 18 July to 19 July, the western part of Beijing-Tianjin-Hebei region was under the control of the trough while the eastern part was controlled by the subtropical high, which was a typical rainstorm pattern in North China. The water vapor transportation was also significantly different. From 15 July to 17 July, the warm wet southwesterly winds and the easterly winds along the periphery of a typhoon provided the main water vapor supply for thunderstorms in Beijing-Tianjin-Hebei region. From 18 July to 19 July, the major moisture supply was provided by warm wet southwesterly winds, which reached East China Sea first and then turned eastward, transporting moisture to Beijing-Tianjin-Hebei region. During the whole week, the center of water vapor convergence appeared near the Beijing-Tianjin-Hebei area, and the water vapor flux and convergence occurred at 1200 UTC were always greater than that at 0000 UTC, which suggested that the water vapor condition in the evening was better than in the daytime. As for the dynamic condition, Beijing-Tianjin-Hebei area was located in the peripheral divergence region of South Asia high, while convergence mainly occurred beneath 700 hPa and was stronger at 1200 UTC. The dry cold downdraft originated from the middle troposphere merged with the moist warm air originated from low levels. The dry cold downdraft descended to lower levels and the convergence was stronger at 1200 UTC. At the same time, vertical temperature difference beneath 800 hPa was stronger at 1200 UTC, which indicated the atmospheric instability was stronger at 1200 UTC. Though the vertical velocity at the upper level at 0000 UTC was stronger than that at 1200 UTC, the vertical velocity at low levels was always stronger at 1200 UTC. In summary, the thermodynamic and moisture conditions were more conducive to thunderstorm occurrence from evening to night.

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History
  • Received:October 14,2016
  • Revised:
  • Adopted:
  • Online: November 10,2017
  • Published: