Numerical simulation of monsoon depressions over India with a high-resolution nested regional model

Abstract

The structure and track of monsoon depressions over India during the summer monsoon have been simulated using a double-nested limited-area numerical weather prediction model. Four distinct cases of monsoon depressions that formed over the Bay of Bengal and adjoining areas have been studied. Initial conditions for the simulations are from either the European Centre for Medium Range Weather Forecasts, Reading, UK or the National Centre for Medium Range Weather Forecasting, New Delhi, India. The model is integrated for up to 48 hours for each case and the results are compared with verification fields. Forecasts of mean sea level pressure and low-level wind indicate that the location of the centres of the depressions and their track could be predicted satisfactorily even though the magnitude of the central pressure is slightly too high. Temperature forecasts show close agreement with the verification analyses and the distribution of precipitation is well simulated. The vertical cross-sections of temperature and wind forecasts show the correct vertical structure. RMS errors of the mean sea level pressure, wind and temperature indicate that the model could simulate the large-scale fields reasonably well. RMS errors of the tracks of the depressions confirm the fact that the high-resolution nested grid model can predict the tracks of the depressions with reasonable accuracy.