Advances in Earth Science ›› 2019, Vol. 34 ›› Issue (12): 1316-1327. doi: 10.11867/j.issn.1001-8166.2019.12.1316

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Dynamic Relationship Between Entrainment Rate and Summer Monsoon in the Transition Area of Monsoon in the East of Northwest China

Yanying Li 1, 2, 3( ),Ying Cai 2,Chunyan Zhang 3,Ting Zeng 3,Jiping Yang 4   

  1. 1.Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province/Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA/ Institute of Arid Meteorology,CMA,Lanzhou 730020, China
    2.Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, CAS, Lanzhou 730000, China
    3.Wuwei Meteorological Bureau in Gansu Province, Gansu Wuwei 733000, China
    4.Minqin Meteorological Bureau of Gansu Province, Gansu Minqin 733300, China
  • Received:2019-09-11 Revised:2019-11-02 Online:2019-12-10 Published:2020-02-12
  • About author:Li Yanying (1970-), female, Wuwei City, Gansu Province, Professor of engineering. Research areas include weather forecasting and research. E-mail: lyyqxj@163.com
  • Supported by:
    the National Natural Science Foundation of China "Study on land-air interaction and its response to summer monsoon in transition area affected by typical summer monsoon in China"(41630426);The Open Fund of the Key Laboratory of Land Surface Process and Climate Change of the Chinese Academy of Sciences "Characteristics of atmospheric boundary layer variation in the East of Northwest China and its response to summer monsoon activities"(LPCC2016005)

Yanying Li,Ying Cai,Chunyan Zhang,Ting Zeng,Jiping Yang. Dynamic Relationship Between Entrainment Rate and Summer Monsoon in the Transition Area of Monsoon in the East of Northwest China[J]. Advances in Earth Science, 2019, 34(12): 1316-1327.

Entrainment rate refers to the ratio of surrounding air quality to air quality involved in rising unit distance, including turbulent entrainment and dynamic entrainment, which are applied to the boundary layer parametrization of convective clouds, the improvement of numerical model, the observation of cloud droplet spectral dispersion and the study of tropical cyclones.Based on the daily data at 07:00 and 19:00 every 10 m of five stations such as Minqin, Yuchong, Pingliang, Yinchuan and Yan'an from May to September during 2006-2016, combined with the daily observation data on the ground, the Entrainment Rates(ER) of different heights were calculated, and the relationships between ER and height in different regions, precipitation as well as monsoon during the monsoon period were further obtained. The main results were as follows: The ER was proportional to air temperature and saturated water vapor pressure, but inversely proportional to relative humidity. The relative humidity threshold of cloud was 65%. The higher the relative humidity threshold was, the lower the cloud height of different orders of precipitation was, and the cloud height was higher with the increase of rainfall. ER had obvious diurnal changes and regional differences: It was obviously smaller at 07:00 than at 19:00 from ground to 3 km, which weakened with the increase of height in the near surface , but strengthened with the increase of height above 500 m; From small to large, the monsoon affected area, the monsoon swing area and the non-monsoon area were in turn, and there was no regional difference above 3 km. ER was closely related to the intensity and property of precipitation in monsoon period. The ER weakened with the enhancement of rain intensity from near ground to below 600 m, but strengthened with the enhancement of rain intensity from 500 m to 2~3 km.From near ground to below 700 m, the ER of stable precipitation was strong, but that of convective precipitation was strong above 700 m. The convective precipitation had big saturated water vapor pressure and strong ER , while the stable precipitation had big saturated water vapor density, rich water vapor but weak ER. The relationship between ER and monsoon as well as its duration: From no monsoon to monsoon ER was weakened, the strongest maximum height was also decreasing. There was no significant difference in the duration of ER between the non-monsoon area and the monsoon affected area, but the longer the monsoon swing area lasted in the near ground layer, the smaller the ER was, while the opposite was at 1~2 km in the high altitude. The relationship between ER and the APO monsoon intensity index showed that: At 07:00, the ER strengthened with height from near ground to below 800 m, but weakened with height above 800 m,and the monsoon intensity was not related to the ER. At 19:00, the ER strengthened with the height near ground but weakened with the height above 300 m, and the stronger the monsoon was, the smaller the ER was. The ER weakened with the decrease of boundary layer height.

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