Initialization of a Mesoscale Model for April 10, 1979 Using Alternative Data Sources

A 35 km grid limited area mesoscale model was initialized with high density SESAME radiosonde data and high density TIROS-N satellite temperature profiles for April 10, 1979. These data sources were used individually and with low level wind fields constructed from surface wind observations. The primary objective was to examine the utility of satellite temperature data for initializing a mesoscale model by comparing the forecast results with similar experiments employing radiosonde data. The impact of observed low level winds on the model forecasts was also investigated with experiments varying the method of insertion. All forecasts were compared with each other and with mesoscale observations for precipitation, mass and wind structure. Preliminary forecasts initialized with radiosonde winds and balanced winds showed that balanced winds substantially reduced initial model shock and provided smoother and more accurate mass fields. The radiosonde and satellite precipitation forecasts differed significantly although both had some very realistic qualities. A low level short wave which was present in both the radiosonde and satellite initial states was retained by the model and propagated around the synoptic scale trough from Oklahoma to Nebraska. The radiosonde short wave was associated with a mesoscale precipitation band that verified with a short wave band evident in radar and SESAME radiosonde observations. The satellite short wave showed a weaker association with a precipitation band, however, the satellite forecast gave a slightly better depiction of convective precipitation over Oklahoma, exhibiting the same general location and orientation as observed. Continuous insertion of low level winds during the initialization period had impacts on mass, wind and precipitation fields. The most dramatic was an improvement in sea level pressure patterns by reducing the fast eastward propagation of the mass field experienced in other forecasts. The model simulated several additional mesoscale features including intensification of a low level dry line and generation of a low level jet. Several forecasts produced convective precipitation systems with characteristics satisfying criteria for a mesoscale convective complex. The study demonstrated that high density satellite temperature data and balanced winds can be used in a mesoscale model to produce forecasts which verify favorably with observations.