Unraveling the spatio-temporal structure of the atmospheric and oceanic intra-seasonal oscillations during the contrasting monsoon seasons

Abstract

Using remotely sensed data sets of rainfall and outgoing longwave radiation (OLR) over Indian land and adjacent oceanic regions and sea surface temperature (SST) over adjacent oceanic regions; we examine the major characteristics of the intra-seasonal oscillations of Indian summer monsoon (ISM) during the flood and drought years. Intra-seasonal oscillations of rain, OLR and SST corresponding to 30–60days transpires to contribute more to the intra-seasonal variability over the Arabian Sea, whereas 10–20days' mode is found to be more dominating over the Bay of Bengal during the drought years. Therefore, suggesting that both of the Seas surrounding the Indian land region respond in a different way to the below normal rainfall conditions of Indian land region. Another important finding of the present work is that during the drought years, 30–60days intra-seasonal oscillations of SST over both of the seas follow the intra-seasonal oscillations of rain at 30–60days' time scale over central India approximately after 26days. Conversely in the flood years, intra-seasonal oscillations of SST at 30–60days over the Arabian Sea and Bay of Bengal lead the intra-seasonal oscillations of rain over central India by 6days. Present analysis also reveals that the intra-seasonal variability of ISM at two different time-scales (10–20 and 30–60days) possess different spatio-temporal characteristics during the contrasting monsoon conditions over the oceanic regions; therefore it is advisable to study the two modes individually for understanding the underlying physical mechanism. Results presented in this paper may be useful for improved ISM prediction.