High-Resolution Subtropical Summer Precipitation Derived from Dynamical Downscaling of the NCEP-DOE Reanalysis: How Much Small-Scale Information Is Added by a Regional Model?

[摘要] This study assesses the regional-scale summer precipitation produced by the dynamical downscaling ofanalyzed large-scale fields. The main goal of this study is to investigate how much the regional model adds smaller scaleprecipitation information that the large-scale fields do not resolve. The modeling region for this study covers thesoutheastern United States (Florida, Georgia, Alabama, South Carolina, and North Carolina) where the summer climateis subtropical in nature, with a heavy influence of regional-scale convection. The coarse resolution (2.5deg latitude/longitude)large-scale atmospheric variables from the National Center for Environmental Prediction (NCEP)/DOE reanalysis (R2) aredownscaled using the NCEP Environmental Climate Prediction Center regional spectral model (RSM) to produceprecipitation at 20 km resolution for 16 summer seasons (19902005). The RSM produces realistic details in the regionalsummer precipitation at 20 km resolution. Compared to R2, the RSM-produced monthly precipitation shows betteragreement with observations. There is a reduced wet bias and a more realistic spatial pattern of the precipitationclimatology compared with the interpolated R2 values. The root mean square errors of the monthly R2 precipitation arereduced over 93 (1,697) of all the grid points in the five states (1,821). The temporal correlation also improves over 92(1,675) of all grid points such that the domain-averaged correlation increases from 0.38 (R2) to 0.55 (RSM). The RSMaccurately reproduces the first two observed eigenmodes, compared with the R2 product for which the second mode isnot properly reproduced. The spatial patterns for wet versus dry summer years are also successfully simulated in RSM.For shorter time scales, the RSM resolves heavy rainfall events and their frequency better than R2. Correlation andcategorical classification (above/near/below average) for the monthly frequency of heavy precipitation days is alsosignificantly improved by the RSM.

[发布日期] 2010-08-10

[学科分类] 大气科学