Some characteristics of Limited-Area Model-Precipitation forecast of Indian monsoon and evaluation of associated flow features

Summary

The Florida State University based Limited-Area Model is in operational use at India Meteorological Department, New Delhi. This paper assesses the performance of the model in temporal and spatial scale to provide 24 hours rainfall forecast over Indian region during south-west monsoon (June to September) and north-east monsoon season (October and November) using three years data (1997–1999). Characteristic features of mean flow pattern produced by the forecast (24 hours) are also examined comparing them with the corresponding analysis fields.

The study demonstrates that performance of the numerical model in predicting precipitation varies with month, geographic location and by synoptic regime. The model, in general, is able to reproduce the spatial pattern of monthly and seasonal rainfall but under-estimates orographic rainfall and over estimates rainfall associated with the monsoon low pressure systems. In October and November when the low pressure belt shifts to the southern latitudes of India, the model is able to capture the heavy rainfall zone confined over south Peninsula. Time series and categorical statistics show that there is a very good correspondence between observed and predicted rainfall.

The other important characteristic features of south west monsoon are well captured by the model and are comparable with the analysis field. But some of the significant deficiencies noticed in the forecast are: higher mean sea-level pressure, particularly over the domain of heat low and relatively weaker lower tropospheric westerlies.

The results of this paper will provide useful input on model performance to operational forecasters and model developers.