Factors influencing strength and variability of Convectively Coupled Kelvin Wave

Abstract

The horizontal structure, propagation characteristics, and the physical processes influencing the strength and interannual variability of convectively coupled Kelvin waves (CCKW) are studied using satellite observation and reanalysis data. An approach of amplitude­based classification of waves is used in this study. The convective signals of CCKW and the major domains of CCKW activity are identified by applying empirical orthogonal function analysis on CCKW wavenumber­frequency filtered OLR anomaly data. The waves are found to be dominant in Pacific and Atlantic domains. The CCKW activity over the Pacific domain exhibited a maximum during the May­June months, whereas the CCKW maximum over the Atlantic domain is during March­May. This suggested that a portion of CCKW over Atlantic might be independent of that over Pacific. Supporting this, the Pacific and Atlantic CCKW variance is identified to have an out of phase relationship during the five strong and weak CCKW activity years in each domain. The amplitudes of Pacific and Atlantic CCKW are found to be indeed depended on the large­scale background state. CCKW amplitude­based composite analysis revealed a strong linear relationship between the amplitude of the CCKWs and El Nino like background state. It was observed that the central Pacific El Nino like background state favors the CCKWs over the Pacific, whereas the eastern Pacific El Nino like background state supports the CCKWs over the Atlantic.