Wave climatology of the Indian Ocean derived from altimetry and wave model

Abstract

GEOSAT altimeter data for the period 1986-1989 have been utilised to derive wave climatology for the Indian Ocean region bounded by 20 degrees S to 25 degrees N and 40 degrees E to 110 degrees E. The results are presented in the form of mean monthly maps, for three typical months representing calm, SW monsoon and NE monsoon seasons. The corresponding in situ values of significant wave height and wave period are grouped into 1 degrees x 1 degrees grid size and averaged grid-wise for each typical month. Similar procedure is followed for Geosat data for comparison purpose. The wave model, WAVEIN has been run using ECMWF winds to hindcast waves over the Indian Ocean and to compare with Geosat wave parameters. As altimeter does not provide wave direction, the same has been generated from the model results to fill up the gaps.Though the Geosat and model wave heights show good match, this could be further improved by reducing the spatial and temporal ranges. Wave periods computed from the Geosat data are found to be low compared to model values. As expected, central Indian Ocean region is found to have higher waves, generally swells, generated by strong winds prevailing over there in all seasons. In July, the entire Arabian Sea is under the influence of high sea states with wave heights exceeding 5 m. SWHs in the Bay of Bengal are less ( less than 3 m) during NE monsoon compared to SW monsoon (approx. equal to 5 m). `Seas' are dominating the north Indian Ocean during February and the Arabian Sea in November. The satellite derived significant wave heights are extremely valuable to evolve long term distribution for generating wave climatology.