Uncertainty in Dust Budget over East Asia Simulated by WRF/Chem with Six Different Dust Emission Schemes

WU Cheng-Lai^1,², LIN Zhao-Hui¹

Figure 2 shows the total dust emission flux simulated by the different schemes. The simulated dust emissions were strongest in the Gobi desert in Mongolia, deserts and sandy regions in northern China, and the Taklimakan desert in northwestern China. Generally, differences in simulated dust emission flux were small in the Gobi and in the regions of western Inner Mongolia, Hetao area and, the Hexi Corridor.
However, large differences in simulated dust emission flux were revealed in the Taklimakan, in the central- eastern region of Inner Mongolia, and in the southwestern region of northeastern China. The GOCART scheme produced dust emission over nearly the entire Taklimakan region, with a magnitude of dust emission flux of 0.1-20 g m -2 . In the remaining five schemes, only scattered dust emissions were simulated in the Taklimakan with a dust emission flux of less than 10 g m -2 , with the exception of a very local flux of 10-100 g m -2 in the eastern part of the Taklimakan simulated by the Shao96 scheme. These results are generally consistent with the remarkable differences in simulated surface dust concentration reported in these regions Fig. 1. The stronger and broader dust emissions in the Taklimakan simulated by the GOCART scheme can be attributed to the lower criteria value of threshold wind velocity used in the scheme, as discussed by Wu and Lin 2013 . It should be noted that LS99, Shao01, and Shao04 schemes produced similar distributions of dust emission because these three schemes are based on the same physical mechanism of saltation bombardment but with different assumptions for vertical dust flux Table 1. 3.2 Regional dust budgets over northern China and Mongolia As shown in Fig. 3, three regions of potential dust sources have been identified for dust budget calculation. Region A 36-44��N, 74-94��E represents western sources; Region B 35-49��N, 94-112��E represents central sources including Mongolia and adjacent Inner Mongolia, in addition to the eastern region of northwestern China; and Region C 40-49��N, 112-126.5��E represents eastern sources including North and northeastern China. Generally, dust budgets over a certain region consist of dust emission E , dust deposition D , inflow and outflow of dust particle transportation, and changes in dust loading C integrated over the entire atmospheric column of the region. As suggested by the wind vector at 850 hPa Fig. 3, dust is mainly transported westward in the lower troposphere in Region A but with eastward transportation in the eastern part of the region. In regions B and C, dust is mainly transported eastward and southward. Table 2 shows the dust budgets over the three regions, and the fractions of total dust emission for individual dust size bins are shown in Table 3. In Region A, the total dust emission simulated during the study period differed significantly among schemes, with maximum total emissions of 2.6 Tg and 2.76 Tg for GOCART and Shao96 schemes, respectively, and mini mum emissions of 0.23 Tg, 0.3 Tg, and 0.56 Tg for LS99, Shao01, and Shao04 schemes, respectively. During the simulation period, the total inflow of dust particles for most dust emission schemes was very low, with magnitudes less than 0.02 Tg. However, the GOCART scheme simulated an inflow of 0.12 Tg, which reflects transportation from a strong dust emission region in Kazakhstan northwest of Region A. Figure 2 Spatial distribution of total dust emission g m -2 simulated with each dust emission scheme during the period of 14-25 March 2002.