This study investigates the capability of the dynamic downscaling method （DDM） in an East Asian climate study for June 1998 using the fifth-generation Pennsylvania State University-National Center for Atmospheric Re...This study investigates the capability of the dynamic downscaling method （DDM） in an East Asian climate study for June 1998 using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research non-hydrostatic Mesoscale Model （MM5）.Sensitivity experiments show that MM5 results at upper atmospheric levels cannot match reanalyses data,but the results show consistent improvement in simulating moisture transport at low levels.The downscaling ability for precipitation is regionally dependent.During the monsoon season over the Yangtze River basin and the pre-monsoon season over North China,the DDM cannot match observed precipitation.Over Northwest China and the Tibetan Plateau （TP）,where there is high topography,the DDM shows better performance than reanalyses.Simulated monsoon evolution processes over East Asia,however,are much closer to observational data than reanalyses.The convection scheme has a substantial impact on extreme rainfall over the Yangtze River basin and the pre-monsoon over North China,but only a marginal contribution for Northwest China and the TP.Land surface parameterizations affect the locations and pattern of rainfall bands.The 10-day re-initialization in this study shows some improvement in simulated precipitation over some sub-regions but with no obvious improvement in circulation.The setting of the location of lateral boundaries （LLB） westward improves performance of the DDM.Including the entire TP in the western model domain improves the DDM performance in simulating precipitation in most sub-regions.In addition,a seasonal simulation demonstrates that the DDM can also obtain consistent results,as in the June case,even when another two months consist of no strong climate/weather events.展开更多
In nested nonhydrostatic mesoscale model MM5,the characteristic quantities of atmospheric turbulence,i.e.,the standard deviations of the turbulent fluctuated speeds for three directions in PBL are computed by Mellor-Y...In nested nonhydrostatic mesoscale model MM5,the characteristic quantities of atmospheric turbulence,i.e.,the standard deviations of the turbulent fluctuated speeds for three directions in PBL are computed by Mellor-Yamada's level 2.5 closure scheme.The magnitudes and the vertical profiles of these quantities computed from the model are closely connected with temperature and wind speed profiles as well as the type of the ground with a significant diurnal variation,and are in agreement with known magnitudes and regularities in different stratification conditions.Hence the method in this paper is reasonable and convincible.Their horizontal distribution depends on the horizontal distribution of the stratification.The method of predicted characteristic quantities of turbulence from mesoscale model in this paper can be used in the problem of atmospheric diffusion and atmospheric environment.展开更多
基金supported by the funding of the Key Program of the Chinese Academy of Sciences (Grant No.KZCX2-YW-328)the National Key Basic Research Program (2005CB422003)+1 种基金National Science Foundation Center of China (NSFC) (40871001)the US JPL Grant No. 1278492,NOAA Grant Nos NA07OAR4310226 and NA08OAR4310591
文摘This study investigates the capability of the dynamic downscaling method （DDM） in an East Asian climate study for June 1998 using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research non-hydrostatic Mesoscale Model （MM5）.Sensitivity experiments show that MM5 results at upper atmospheric levels cannot match reanalyses data,but the results show consistent improvement in simulating moisture transport at low levels.The downscaling ability for precipitation is regionally dependent.During the monsoon season over the Yangtze River basin and the pre-monsoon season over North China,the DDM cannot match observed precipitation.Over Northwest China and the Tibetan Plateau （TP）,where there is high topography,the DDM shows better performance than reanalyses.Simulated monsoon evolution processes over East Asia,however,are much closer to observational data than reanalyses.The convection scheme has a substantial impact on extreme rainfall over the Yangtze River basin and the pre-monsoon over North China,but only a marginal contribution for Northwest China and the TP.Land surface parameterizations affect the locations and pattern of rainfall bands.The 10-day re-initialization in this study shows some improvement in simulated precipitation over some sub-regions but with no obvious improvement in circulation.The setting of the location of lateral boundaries （LLB） westward improves performance of the DDM.Including the entire TP in the western model domain improves the DDM performance in simulating precipitation in most sub-regions.In addition,a seasonal simulation demonstrates that the DDM can also obtain consistent results,as in the June case,even when another two months consist of no strong climate/weather events.
基金This work was supported by National Natural Science Foundation of China under Grant No.49875005.
文摘In nested nonhydrostatic mesoscale model MM5,the characteristic quantities of atmospheric turbulence,i.e.,the standard deviations of the turbulent fluctuated speeds for three directions in PBL are computed by Mellor-Yamada's level 2.5 closure scheme.The magnitudes and the vertical profiles of these quantities computed from the model are closely connected with temperature and wind speed profiles as well as the type of the ground with a significant diurnal variation,and are in agreement with known magnitudes and regularities in different stratification conditions.Hence the method in this paper is reasonable and convincible.Their horizontal distribution depends on the horizontal distribution of the stratification.The method of predicted characteristic quantities of turbulence from mesoscale model in this paper can be used in the problem of atmospheric diffusion and atmospheric environment.
