Long period waves in the coastal regions of north Indian Ocean

Abstract

The sea surface height (SSH) anomaly derived from TOPEX/POSEIDON altimeter was used to study the characteristics of long period waves in the coastal belt of north Indian Ocean. Wavelet analysis at typical locations revealed that the most dominant signals were in the bands of intra-seasonal oscillation (ISO), i.e. 30-60 days, 3-4 months, semi-annual and annual. Among them, the annual signal contained maximum energy at all the locations. But, inside the Andaman Sea, and off the Gulf of Aden, the ISO component is of nearly equal magnitude as that of annual. In the regions of large SSH variability, low frequency components (more than 3 months) dominated, whereas they contained less energy in the region of minimum SSH variability. Hovmullor diagrams revealed large inter- and intra-annual variability in the SSH fields. In general, along the eastern boundary of the ocean, high sea level was observed during April-June and October-December in association with equatorial Kelvin waves. Another notable observation was the formation of high SSH in the western Indian Ocean during February-May and August-October. Among them, the former one propagated northward while latter one was found stationary. The Markan coast was found as the region of meeting place of two waves, one from the western Indian Ocean and the other from the eastern Bay. The results can be utilized to enhance the understanding of various coastal processes controlled by long period waves, viz. upwelling, sinking, circulation and meso-scale features.