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Journal of Desert Research ›› 2019, Vol. 39 ›› Issue (2): 122-133.DOI: 10.7522/j.issn.1000-694X.2018.00054

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The Gale Concentration Period and Degree over the Tibetan Plateau and Related Atmospheric Circulation during the Windy Period

Yao Huiru1,2, Li Dongliang1   

  1. 1. College of Atmospheric Science/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China;
    2. Meteorological Disaster Prevention Technology Center of Tianjin, Tianjin 300202, China
  • Received:2018-02-27 Revised:2018-04-27 Published:2019-04-11

Abstract: Based on the daily maximum wind speed data of 47 stations in the Tibetan Plateau and JRA-55 reanalysis data, by using the concept of concentration period and concentration degree, the concentration of gales over the Tibetan Plateau and related atmospheric circulation during windy period from 1971 to 2012 are analyzed. The results show that the gales over the Tibetan Plateau occur mostly in spring (from March to May) and occur least from August to October. There is a declining trend of the gale days during 1971-2012 with a rate of -14 d/10a, and the annual range of the gale days is also reduced. The gale concentration period (GCP) over the Plateau is usually delayed with latitude and is moving up earlier in the recent 42 years, which is from the early April to early March. The gale concentration degree (GCD) has an increase tendency, and it depends on the number of gale days. The more the gale days are, the lower the concentration degree is. GCP is affected by the meridional displacement of the subtropical jet stream. In February and March, when the subtropical jet stream in North Africa and Western Asia and the low-level westerly belt in April tended to be southerly, along with the lower pressure in the subtropical region, there is more gale days over the Tibetan Plateau and GCP is delayed; Otherwise, GCP is advanced. GCD is related to the intensity of the subtropical jet stream in Central Asia and Tibetan Plateau from February to April. When the subtropical jet in February and April is weak and the jet in March is strong, the gale days over the plateau are concentrated in March and the GCD is high, and vice versa. In spring, especially in March, the occurrence of gales over the Tibetan Plateau is the result of the interaction of cold and warm air system. The gales in the eastern plateau are affected mostly by the cold air from the North, while the gales in the west of the plateau are influenced by the warm air from the South, which is dominated by the southwest wind.

Key words: Tibetan Plateau, gale days, concentration period, concentration degree

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