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NESTED GRID MESOSCALE ATMOSPHERIC CHEMISTRY MODEL
Citation:
Pleim, J., J. Chang, AND K. Zhang. NESTED GRID MESOSCALE ATMOSPHERIC CHEMISTRY MODEL. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-91/192 (NTIS PB91233551), 1991.
Description:
A nested grid version of the Regional Acid Deposition Model (RADM) has been developed. he horizontal grid interval size of the nested model is 3 times smaller than that of RADM (80/3 km 26.7 km). herefore the nested model is better able to simulate mesoscale atmospheric processes while maintaining consistency with larger-scale features. he nested model uses dynamic boundary conditions along inflow boundaries which arc interpolated from coarse grid model (RADM) results. ince the nesting is one-way, the outflow boundary conditions art specified to minimize numerical reflections. hree-day wet deposition amounts of sulfate and nitrate simulated by the nested grid version of RADM as well as the coarse grid version were compared to measurements made by the regional scale network during the Oxidizing and Scavenging Characteristics of April Rains (OSCAR) IV experiment. oth models were able to predict wet depositions of sulfate to within a factor of 2 for over 8O% of the sampling sites. itrate predictions were slightly worse with just over 70 of the pairs within a factor of two for both models. lthough the nested grid model showed no improvement over the coarse grid model in terms of point by point comparisons, it did demonstrate the ability to predict a more realistic range and spatial variability of wet deposition amounts. Plots of predicted deposition fields show that the nested model predicted values similar to the observations in their vicinity more often than did the coarse grid model. ested model simulations of wet deposition were also compared to measurements made by a high density sampling network over a 110 x 110 km area of northeastern Indiana. ost of the spatial features of the observed distribution wert well simulated by the model demonstrating the nested model's ability to resolve processes on scales which art subgrid to the coarse grid model. he predictions of wet depositions by both models were in better agreement with observations than were predictions of precipitation. ince the OSCAR IV experiment was characterized by very efficient washout, the rate of wet deposition was often primarily controlled by the rate of supply of airborne material to the precipitating system rather than aqueous oxidation and precipitation processes. herefore errors in precipitation rate had little impact on wet deposition predictions.
