Study on dust occurrence and transportation related to boundary layer height in Northwest China. (24th February 2022) - Tan, Ziyuan
Abstract: Boundary layer development has a significant influence on dust emission and transportation. The effects of surface heat flux on distribution of dust related to BLH (boundary layer height) during a dust event in Northwest China are discussed by numerical simulation. The results show that: the dust emissions start in Dunhuang and strengthen in Minqin with large dust emission fluxes (as high as 3000 μg m −2 s −1 ) and surface wind speed (up to 20 m s −1 ). The dust at the early stage mainly concentrates below 500 m above the ground, then lifts over 3000 m above the ground at the strengthening stage, and the concentration in high value center is more than 24, 000 μg m −3 at the dust source Dunhuang. The high dust concentration in Minqin maintains at about 1000 m above the ground. Weak dust emission in Minqin makes the dust concentration near the ground less than that in the upper air. The BLH in the high dust concentration center is higher than that in the surrounding area at the emission stage in Dunhuang. Sensitivity experiment with turning off surface heat flux shows obvious decrease of the dust concentration in Dunhuang, with more than four times reduction of the surface dust concentration. The BLH near the high dust concentration area reduces significantly in the sensitivity experiment. However, the gap between the two experiments reduces with the dust development. The BLH in the sensitivity experiment has small spatial differences with uniform distribution in Dunhuang. It means that the thermodynamic contribution is main reason for the distribution differences. The two experiments in Minqin also show that the height of high concentration dust has a difference of about 500 m. The dust lifts with the boundary layer development, but shows different distribution characteristics and influencing factors between Dunhuang and Minqin. Abstract : Distribution characteristics of a dust related to its boundary layer height and effects of surface heat flux are discussed by numerical simulation during a dust event in Northwest China. At the source Dunhuang, the dust mainly concentrates below 500 m above the ground at the early stage, then lifts over 3000 m at the strengthening stage. At the transport point Minqin, the high dust concentration maintains at about 1000 m above the ground. The boundary layer height in the high dust concentration center is higher than that in the surrounding area at the emission stage. Sensitive experiment without the surface heat flux shows obvious decrease of the dust concentration in Dunhuang, more than four times reduction of the surface dust concentration. The boundary layer height in the sensitive experiment has small spatial differences with uniform distribution. It means that the thermodynamic contribution is a main reason for the distribution differences of the boundary layer height which has a significant influence on the dust diffusion range and vertical distribution.