Report on Project WIND - Preliminary Experiments with the UK Meteorological Office Mesoscale Model - September 1987.
READING UNIV (UNITED KINGDOM) DEPT OF METEOROLOGY
The Meteorological Office MO mesoscale model has been run for the simulation of the summer flow on 27 June 1985 in the Sacramento Valley, California. The purpose is to examine its predictive capability using the meso-Beta high resolution observations that were obtained during Phase I of U.S. Army Project WIND and compare with it similar runs made with the ASL SIGMET model. The simulated region is a 460 X 460 km area centered at 39.75 N, 121.8 W as in the SIGMET simulation by Williams et al., 1986. Three simulations were performed with the same topography, horizontal grid spacing Delta-x Delta-y 20 km and period of integration, and also the same radiosonde initialization that for Orchard, 1700 GMT as in the SIGMET run. Fig. 1 illustrates the topography of the region, which includes an artificial apron following the SIGMET run. Three simulations were performed and their characteristics are summarized in Table 1. In the first simulation, the MO model was modified to run with vertical levels as in the SIGMET run 36, 116, 213, 330, 471, 4779, 6219 m while the other experiments, Nos. 2 and 3, were run with the vertical spacings and number of levels 16 used by the operational MO mesoscale model simulations. In the third run the evaporation resistance was increased from 100 to 500 sm resulting in effectively reducing the evaporation to nearly zero. This reflects the relatively dry conditions over the Sacramento Valley at that time.