Bhanu Kumar, O S R U, S Ramalingeswara Rao and S S Raju
Keywords: Convective activity, circulation changes, variability.
Abstract: In this study satellite derived Outgoing Long wave Radiation (OLR) and National Centre for Environmental Prediction (NCEP) reanalysis zonal wind (U-850 and U-200 hPa levels) datasets for 27-years are used to examine important and unique characteristics of summer monsoon circulation variability across India. Among mean 73 pentads of annual cycles for OLR and zonal wind components, large scale monsoon convective activity, monsoon westerlies at 850 hPa and strengthening of easterlies at 200 hPa levels are conspicuously represented by P-30 to P-55 pentads over India. More details of monsoon circulation change are inspected in spatial distribution of OLR and wind fields for the climatological annual cycles. The OLR field is inversely related with U-850 hPa, while it is directly related with U-200 hPa levels; both are statistically significant at 0.1% level in this study. Annual cycles of the OLR and wind fields (anomaly) reveal striking interannual monsoon circulation variability in El Nino (2002) and La Nina (1998) years. The monsoon seasonal circulation changes in above contrasting years are highlighted and they reveal that U-850 hPa is almost a mirror image of U-200 hPa distribution of wind fields over the monsoon region. Finally the strength of ISO index in terms of Monsoon Hadley Index (MHI) and Madden and Julian Oscillation (MJO) index are evaluated to study year-to-year monsoon variability across India. Above ISO indices are related with Indian summer monsoon rainfall and the relationships are statistically significant.
[View Complete Article]