Abstract
Abstract. Dust in snow on the Tibetan Plateau (TP) could reduce the visible snow albedo by changing surface optical properties and removing the snow cover through increased snowmelt, which leads to a significant positive radiative forcing and remarkably alters the regional energy balance and the eastern Asian climate system. This study extends our previous investigation in dust–radiation interactions to investigate the dust-in-snow radiative forcing (SRF) and its feedbacks on the regional climate and the dust cycle over eastern Asia through the use of the Community Atmosphere Model version 4 with a Bulk Aerosol Model parameterizations of the dust size distribution (CAM4-BAM). Our results show that SRF increases the eastern Asian dust emissions significantly by 13.7 % in the spring, countering a 7.6 % decrease in the regional emissions by the dust direct radiative forcing (DRF). SRF also remarkably affects the whole dust cycle, including transport and deposition of dust aerosols over eastern Asia. The simulations indicate an increase in dust emissions of 5.1 %, due to the combined effect of DRF and SRF. Further analysis reveals that these results are mainly due to the regional climatic feedbacks induced by SRF over eastern Asia. By reducing the snow albedo over the TP, the dust in snow mainly warms the TP and influences its thermal effects by increasing the surface sensible and latent heat flux, which in turn increases the aridity and westerly winds over northwestern China and affects the regional dust cycle. Additionally, the dust in snow also accelerates the snow-melting process, reduces the snow cover and then expands the eastern Asian dust source region, which results in increasing the regional dust emissions. Hence, a significant feature of SRF on the TP is the creation of a positive feedback loop that affects the dust cycle over eastern Asia.
Highlights
A large amount of desert dust from eastern Asian arid and semiarid regions is emitted into the atmosphere, which can be carried over the wide downwind regions, including eastern China and the Pacific Ocean, and deposited in snow over the Tibetan Plateau (Wake et al, 1994; Zhang et al, 1997; Zhao et al, 2006)
In our previous study (Xie et al, 2018), we showed, using the improved Community Atmosphere Model version 4 with a Bulk Aerosol Model parameterization of the dust size distribution (CAM4-BAM), that direct radiative forcing (DRF) decreases the eastern Asian dust cycle owing to the negative surface radiative forcing through the PBL mechanism, which counteracts northern African dust emissions induced by DRF
A large amount of desert dust from eastern Asian arid and semiarid regions is deposited on snow over the Tibetan Plateau (TP)
Summary
A large amount of desert dust from eastern Asian arid and semiarid regions is emitted into the atmosphere, which can be carried over the wide downwind regions, including eastern China and the Pacific Ocean, and deposited in snow over the Tibetan Plateau (Wake et al, 1994; Zhang et al, 1997; Zhao et al, 2006). There exists a larger amount of deposition on snow of black carbon and dust aerosols over the TP due to the high industrial and natural emissions in Asia from observational studies (Xu et al, 2009; Ming et al, 2013; Qu et al, 2014; Lee et al, 2017; Li et al, 2018; Zhang et al, 2018) Over this region, the particles of dust are the dominant insoluble impurities compared with black carbon in terms of particle mass (Ming et al, 2013; Qu et al, 2014). In our previous study (Xie et al, 2018), we showed, using the improved Community Atmosphere Model version 4 with a Bulk Aerosol Model parameterization of the dust size distribution (CAM4-BAM), that DRF decreases the eastern Asian dust cycle owing to the negative surface radiative forcing through the PBL mechanism, which counteracts northern African dust emissions induced by DRF.
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