In this study a non-hydrostatic version of the PSU/NCAR Betts-Miller (or Grell) schemes as PBL and convection parameterisation schemes respectively are best compared to the other schemes used in this study.

Accurate prediction of thunderstorms during the pre-monsoon season (April-June)

The rainfall associated with the Indian summer monsoon shows large intraseasonal and interannual variability. Breakmonsoon conditions are one of the important epochs of the monsoon, and they contribute significantly to the intraseasonal variability of the monsoon. The National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis data sets are used to investigate the significant energy budget terms during the pre-break (5 days prior to the commencement of the break), break and post-break (5 days after the cessation of the break) periods. In the present study, certain dynamic and thermodynamic characteristics of the monsoon circulation during break-monsoon conditions are investigated. The important terms in the various energy budget equations are analysed between the surface and 100 hPa for the break and its departures from pre-and post-break for the period 1968-96. The statistical significance of these departures is also examined by Student's t-test at the 95% confidence level. The volume integral of the budget terms is also examined in four sectors, i.e. the Arabian Sea, Bay of Bengal, northern India and central India.Significant changes in the wind field and vorticity at 850 hPa take place in the monsoon trough zone, coastal regions of the western coast of India and the southwestern Bay of Bengal off the southern Indian coast. The vertically upward rising arm of the Hadley cell weakens during the break phase. The strong flux convergence of kinetic energy in the central Arabian Sea and flux divergence in the northeastern Bay of Bengal weakens during pre-and post-break periods. Significant changes in the diabatic heating horizontal flux of heat and moisture are observed in the monsoon trough zone, central and northwestern Bay of Bengal. The Bay of Bengal and central India sectors show higher magnitudes and changes in respect of dynamic and thermodynamic parameters compared with the Arabian Sea and northern India.

The south-west monsoon (June-September)

In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields and heat budget components) over monsoon region (30 • E-120 • E, 30 • S-30 • N) during the pre-monsoon month of May and summer monsoon season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for 42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon years in the surface meteorological fields are also examined by Student's t-test at 95% confidence level. Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2 m) in the month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2 m) in the month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows positive anomalies over NW India and north Arabian Sea. There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered as an advance indicator of the possible behavior of the subsequent monsoon season. The distribution of net heat flux is predominantly negative over eastern Arabian Sea, Bay of Bengal and Indian Ocean. Anomaly between the two extreme monsoon years in post 1980 (i.e., 1988 and 1987) shows that shortwave flux, latent heat flux and net heat flux indicate reversal in sign, particularly in south Indian Ocean. Variations of the heat budget components over four smaller sectors of Indian seas, namely Arabian Sea, Bay of Bengal and west Indian Ocean and east Indian Ocean show that a small sector of Arabian Sea is most dominant during May and other sectors showing reversal in sign of latent heat flux during monsoon season.