Wet Deposition. Dust Model Parameters And Simulation Of The Process

According to available study and researches: up to now, there are only a few dust models, which takes wet deposition into consideration. This is because of the lack of understanding about microphysical Mechanism of dust and sand storms, and the fact that dusty weather rarely occurred at the same time with precipitation. Though some dust models did consider precipitation factor, they still have some imperfections, such as the parameterization process is relatively simple, or the physical rationality need to be improved.Based on studying the domestic and international theory of solid aerosol's wet cleansing, and considering the physical mechanism, practicability, and the characteristics of a "Integrated Dust Model System", we designed a parameterized scheme for dust aerosol's wet deposition. In the scheme, we considered the pulling and cleansing effects of simulated grid-scale precipitation both in and under clouds; distinguished the cleansing effects of rain and snow, As calculating the wet deposition effects caused by snow, we took the direct effects of temperatures into consideration. Supposing that the level of free convection is equal to the cloud bottom level, we considered the pulling effects of simulated sub-grid scale precipitation, which is under clouds. Up to this point, we finished the design of parameterized scheme for wet deposition.Based on Zhao Lima's study result (NMC;2002), taking use of the daily running integrated dust model system, which was established by using local resources, and according to the characteristics of this dust model system, which doesn't considers the precipitation factor, we designed this parameterized scheme and introduced it into the integrated dust model system. Through altering the main programming of the weather model in the integrated dust model system and displaying the main programming of both water vapor and convection parameterized schemes, we calculated and provided the data about precipitation intensity. Through altering the main programming of dust transport model, we calculated the effects of wet deposition, and output wet deposition flux. Up to this point, we have completed the work of introducing the parameterized scheme into the dust model.Taking two dusty weather process appearing over China as test examples, which were accompanied by precipitation and appeared in April, 2003 and March 2004 respectively, using the parameterized wet deposition scheme designed by us, wecarried out simulated numerical tests to check the design of the parameterized scheme and the process of introducing the scheme into dust model, as well as to analyze the influence of wet deposition on simulated dust concentration and the susceptibility of wet deposition toward simplified rain-cleansing coefficient schemes. The 3 groups of numerical simulated tests are: controlling tests which considers wet deposition process, comparison tests which didn't consider the precipitation factor, and susceptibility tests which used different rain-cleansing coefficient schemes to calculate rain cleansing effects. The result is: both the design of the parameterized scheme and the process of introducing the scheme to the dust model are correct. The wet deposition caused by the precipitation pulling effects had a relatively noticeable influence on the distribution of dust aerosols, (mainly to decrease the simulated dust concentrations), and this influence can be found in the atmosphere from surface all the way up to the low troposphere. Over precipitation areas, wet deposition has almost the same effect as dry deposition. And as precipitation level was relatively low, wet deposition is not very sensitive to rain-cleansing coefficient schemes.