Author(s)

Xiaoyan Gong

Affiliation(s)

Space Science and Applied Research Center, Chinese Academy of Sciences, Beijing 00190, China.

Corresponding Author

Xiaoyan Gong

ABSTRACT

The entrainment rate refers to the ratio of the surrounding air mass to the air mass involved in the rising unit distance, including turbulent entrainment and dynamic entrainment. It is applied to the boundary layer parameterization of convective clouds, numerical model improvement, and observation of cloud droplet spectrum dispersion and tropical cyclone studies. Using the high-altitude intensive observation data at 07:00 and 19:00 every day from May to September 2006 to September 2016 in the monsoon transition zone in the northwestern part of Minqin, Yuzhong, Pingliang, Yinchuan, and Yan'an, combined with the daily observation data on the ground, calculate the entrainment rate at different heights, and obtain the relationship between entrainment rate and height, monsoon precipitation and monsoon in different regions. The results show that: ① The entrainment rate is directly proportional to air temperature and saturated water vapor pressure, but inversely proportional to relative humidity. The relative humidity threshold of clouds is 65%. The higher the relative humidity threshold, the lower the cloud heights of different magnitudes of precipitation, and the cloud heights increase with the increase of rainfall. ② There are obvious early-night changes and regional differences in the entrainment rate: from the surface to 3 km, at 07 o'clock is significantly smaller than at 19 o'clock, the near-surface layer weakens with increasing altitude, and increases with altitude above 500 m; from small to large is the monsoon affected area, monsoon swing area and non-monsoon area, there is no obvious regional difference above 3 km. ③ The entrainment rate is closely related to the intensity and nature of precipitation: the entrainment rate decreases with the increase of rain intensity from near the ground to below 600m, but increases with the increase of rain intensity from 500m to 2-3 km; Stable precipitation below has strong entrainment, while convective precipitation above has strong entrainment. Convective precipitation has high saturated water vapor pressure and strong entrainment, while stable precipitation has high saturated water vapor density and rich water vapor but weak entrainment. ④ The relationship between the entrainment rate and the monsoon and its duration: the entrainment rate weakens from no monsoon to monsoon presence, and the maximum height of the strongest entrainment also decreases. There is no obvious difference in the duration of the entrainment rate between the non-monsoon area and the monsoon-affected area. Only in the monsoon swing area, the longer the duration near the surface, the smaller the entrainment rate, and the opposite is true at 1-2 km high. ⑤ The relationship between the entrainment rate and the Asian-Pacific Oscillation (APO) monsoon intensity index shows that: at 07:00, the near-surface layer increases with height, and above 800 m, it weakens with height, and the correlation between monsoon intensity and entrainment rate is not obvious; at 19:00, the near-surface It increases with altitude, and weakens with altitude above 300 m, and the stronger the monsoon, the smaller the entrainment rate. The entrainment rate decreases as the boundary layer height decreases.

KEYWORDS

Entrainment rate; Summer monsoon; Dynamic relationship; Monsoon transition zone; Northwestern and eastern.

CITE THIS PAPER

Xiaoyan Gong. Relationship between entrainment rate and summer monsoon dynamics in the eastern northwest monsoon transition region. Academic Journal of Earth Sciences. 2023, 1(1): 10-15.

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