| Dust cycle including dust emission,transport and deposition,as the primary part of dust cycle,dust emission affects the next two parts,is the basis of study on the dust and global changes.The Taklimakan Desert is one of the major dust sources in China and East Asia.However,the lack of systematic study on the dust emission processes caused poor simulated results of it for all the main parameterization schemes of dust emission.In view of this,the March 2008 to February 2018 data of dust emission,microclimate and soil environment are used to analyze the dust emission processes and characteristics,investigate effects on dust emission by precipitation,soil moisture,air humidity and temperature,obtain the key parameters including surface roughness,dust emission thresholds and dust emission fluxes,and so on,establish and correct parameterization schemes of soil moisture effect on dust emission thresholds,horizontal and vertical dust fluxes combining wind tunnel tests,carry out localization improvement of parameterization scheme of dust emission and sand-dust numerical model of Xinjinag.Conclusions mainly indicated that at the study site:(1)These data suggested that dust emission time in study area were 3609.8 hours,accounting for more than 4.1%of the total time during ten years,and a single dust emission event could continue for four hours.Dust emission amounts and time all displayed clear seasonal variations in the following rule:summer(49.6/45.1%)>spring(40.0/39.2%)>autumn(8.7/11.8%)>winter(1.7/3.8%).Diurnal variations of dust emission amount and time presented an unstandard bell-shaped with some fluctuations,the data showed that 79.6and 78.7%of the total dust emission amount and time occurred during daytime(08:00–20:00LST),and only 20.4 and 21.3%of them occurred at night and early morning(20:00–08:00LST).The ratio between dust emission amount on dust and non-dust days was 89.8:10.2,and the ratio of the dust emission time was 77.4:22.6.The inhibition effect of a rain event on the dust emission has totally disappeared in about 24 h in after a rain event,however the inhibition effects of rain events on the seasonal dust emission were inapparent.(2)In study area,threshold velocity for 2 m heights ranged between 4.0 and 6.0 m/s,and threshold friction velocity ranged between 0.24 and 0.36 m/s.The threshold for soil moisture to affect the dust emission thresholds was about 0.025 m3/m3.During a single sandstorm process,the horizontal dust flux that passed through a section of 100 cm in width and 200 cm in height could reach 459.4 kg,the vertical dust flux could reach 3.69 kg/m2,and that of PM20was 9.79×10-2kg/m2,respectively.(3)The parameterization schemes of soil moisture effect on dust emission thresholds were corrected,and a new parameterization scheme was established,the corrected and new parameterization schemes have lowered the sensibility of dust emission thresholds on soil moisture.The parameterization schemes of horizontal dust flux were also corrected,and a new parameterization scheme was also established,the optimizing order of parameterization schemes of horizontal dust flux was corrected scheme based on wind tunnel test of White,original scheme of Owen and new scheme based on field experiments.The parameterization scheme of vertical dust flux was also corrected.(4)After localization improvement of parameterization scheme of dust emission,dust emission threshold,horizontal and vertical dust flux changed significantly.After localization improvement of air density,dust emission thresholds differed 1.5 to 10.9%from original value,horizontal dust fluxes differed 11.4 to 299.0%from original value.After localization improvement of surface roughness,dust emission thresholds differed 19.0 to 33.2%from original value,horizontal dust fluxes differed 42.2 to 425.7%from original value.After localization improvement of smooth surface roughness,dust emission thresholds differed 0.4to 4.6%from original value,horizontal dust fluxes differed 1.8 to 19.9%from original value.After localization improvement of soil moisture,dust emission thresholds decreased 32.1 to49.5%,horizontal dust fluxes increased 65.8 to 69.2%when gravimetric soil moisture was lower than 5.0%.After localization improvement of parameterization scheme of horizontal and vertical dust flux,them decreased 300.0 and to 90.0%,respectively.After localization improvement of surface soil particle size distribution data,horizontal dust fluxes differed 9 to15 times from original value.(5)By means of localization improvement of parameterization scheme and replacement of the parameterization schemes of surface roughness element effect on dust emission thresholds,the simulated results of horizontal dust flux were significantly improved.Localization improvement of Xinjiang dust numerical model could improve the simulated results of dust concentration and scope of dust emission over the Taklimakan Desert. |
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