Intraseasonal Convection and Air–Sea Fluxes Over the Indian Monsoon Region Revealed from the Bimodal ISO Index

The present study aims to elucidate the intraseasonal oscillations (ISO) of atmospheric convection and air–sea fluxes over the Indian region during summer monsoon season. To accomplish this, the study employs the extended empirical orthogonal function-based bimodal ISO index developed by Kikuchi et al. [Clim Dyn 38(9–10):1989–2000, 2012]. The propagation of deep convective anomalies and air–sea fluxes are explored during the different phases (P1–P8) of the bimodal index. This is achieved by examining the Tropical Rainfall Measuring Mission satellite rainfall, outgoing long-wave radiation (OLR), sea surface temperatures (SST), downward shortwave radiation (DSR) and reanalysis products of 850-hPa winds, potential vorticity and latent heat fluxes (LHFs). Composite analysis of the anomalies depicts the strong (weak) northward (eastward) propagation of convective anomalies over the Indian region (equatorial Indian Ocean). Over the Indian region, active (suppressed or weak) convection is evident during the phases of P4 and P5 (P1, P2 and P7, P8). Enhanced deep convection is lead by a phase of 850-hPa westerly winds and negative SST anomalies. Signatures of ISO during different phases are examined from Research Moored Array for African-Asian-Australian Monson Analysis and Prediction (RAMA) buoy observations over the Bay of Bengal. Rainfall, SST and LHF anomalies from RAMA buoy measurements are in concurrence with the spatial composites of bimodal ISO phases. Plausible drivers for the variability of intraseasonal convection and air–sea fluxes were reviewed using published observational and modelling studies. Findings from the present study advocate the applicability of Kikuchi bimodal index [Clim Dyn 38(9–10):1989–2000, 2012] over the Indian region and have practical application for the validation of ocean-atmospheric coupled models.