An Improvement of the Vertical Interpolation Method for the Initial Field of a Regional Model

Abstract

The “increment” method in the p-sigma conversion to obtain the initial fields is applied to a regional model in order to get more realistic initial planetary boundary layer (PBL). This method vertically interpolates the increment, i. e , the difference between the analysis and the forecast of previous run, while the operational method interpolates the analysis only. Forecast experiments are carried out for two cases in winter, in order to investigate the impact of the method on the initial and forecast fields. Results are compared with those by the operational method. Initial fields by the increment method can maintain fairly well the mixed layer over the warm sea and the stable layer above the cold continent. The patterns are much close to the observations. In another case, the initial moisture and wind fields around a cyclone become more realistic by the increment method. The improvements on the initial fields affect not only the spin-up time of precipitation but also the development of a cyclone.