Spatio-Temporal Distribution and Variability of High Threshold Wind Speed and Significant Wave Height for the Indian Ocean

Space-borne satellites provide extensive coverage of measuring sea surface wind field and wave heights on a global scale. The present study provides a comprehensive assessment of distribution of extreme wind and wave fields over the Indian Ocean (IO) utilizing satellite-based scatterometer and altimeter datasets. Merged scatterometer data from ERS-1/2, QuikSCAT, and ASCAT for a period of 27 years produced continuous record of wind speed, whereas the calibrated altimeter data for different satellite missions provided information on the significant wave height. A comparison study between merged scatterometer and calibrated altimeter derived long-term maximum wind speed shows an overestimation of altimeter product by an average measure of 3 m/s and higher as compared to the scatterometer winds in 92.8% of the total observational points considered. A decadal variability was observed in the inter-annual spatial distribution of the 90th and 95th percentile winds for the study region. Interestingly, the study reveals a declining trend in the dispersion of higher waves (90th, 95th, and 99th percentiles) in the entire IO except the South China Sea. Further, 2011 onwards there is an increasing trend in the annual distribution of extreme winds and waves for the Extra-tropical South Indian Ocean having implications on the generation of swell wave fields.