Gustiness and Coherent Structure of Strong Winds and Their Role in Dust Emission and Entrainment

Authors: 

ZENG Qingcun¹ (曾庆存), CHENG Xueling¹ (程雪玲),HU Fei^*1 (胡 非), and PENG Zhen² (彭 珍)
¹ Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
² Department of Atmospheric Science, Nanjing University, Nanjing, Jiangsu 210093

Abstract:

After the passage of a cold front, spring in northern China, the outbreak of strong wind is often accom-panied by dust emissions. Through analyses of data in the atmospheric boundary layer during a typical case, it is revealed there are rather regular gust wave packets superimposed on the basic strong wind flow.The gust-wind wave packets have a period equal to around 3{6 mins and possess coherent structure. As the vertical transport of momentum is decomposed into separate parts by (a) basic flow, (b) gust-wind,and (c) turbulence, they are all in a downwards direction at the lower levels of the atmospheric boundary layer during strong wind periods. However, (a) is the largest, while (b) and (c) are comparable. All these are very di®erent from the case of normal weather. Besides, the friction velocity at the ground surface is also much larger than that of normal weather and should be corrected by taking the contributions of the basic flow and gust-wind into account.The strong basic flow with descending motion is very favorable for soil erosion and sand/dust emissions, but suppresses the entrainment of dust particles by keeping them within the bottom levels of the atmospheric boundary layer. Owing to the coherent structure of gust-wind, dust particles can e®ectively overcome the systematic descending air motion and penetrate into the middle and upper levels of the atmospheric boundary layer, and then propagate further and di®use into the troposphere where ascending air motion prevails.

Keywords:

gust-wind, coherent structure, descending motion, dust storm, soil erosion, dust entrainment

Citation:

Zeng, Q. C., X. L. Cheng, F. Hu, and Z. Peng, 2010: Gustiness and coherent structure of strong winds and their role in dust emission and entrainment. Adv. Atmos. Sci., 27(1), 1{13, doi: 10.1007/s00376-009-8207-3.