Relationships between the development of convective mixed layer and the occurrence of dust weather in arid and semi-arid regions of East Asia
We statistically described the relationship between the convective mixed layer and the dust weather over the arid and semiarid regions in East Asia by using operational surface-station observation data. In this study, we used the lifting condensation level (LCL) height as a substitute for the mixed-layer height. We divide East Asia area into 5 regions (west / east Taklamakan Desert, west / east Gobi Desert, northeast China) and have classified dust weather into three categories (floating dust, blowing dust, dust storm). We found that the relationship between the number of occurrences of the three types of dust weather and the daily maximum LCL height appears differently depending on the 5 regions. Floating dust occurs the most frequently in west Taklamakan Desert. In Taklamakan Desert, all the dust weather types occur even at low wind speeds, and they seldom occur if the daily maximum LCL height is lower than about 1000 m. The floating dust events spread widely inside the Tarim basin, once they occur. In Gobi Desert, when the maximum LCL height reached about 3000 m, all the dust weather types tend to spread within the region. In northeast China, dust weather occurrence is less frequent than in the other desert regions. Furthermore, our results indicated that the daily maximum LCL heights are higher in the dust weather categories than in the no-dust weather category in all the analysis regions. When severe dust weather occurred in Taklamakan and Gobi Desert, the maximum daily LCL heights reached around 4000-5000 m above the mean sea level under higher wind conditions. It is suggested that during the occurrence of dust event in well-developed mixed-layer conditions, dust particles are easily raised from the boundary layer into the free troposphere, which is favorable for long-range transport of dust aerosols in East Asia and farther.