Wind-generated wave climate variability in the Indian Ocean using ERA-5 dataset

The present study analyzed 41 years of ERA-5 wind-wave data (1979-2019) to understand the long-term trend, inter-annual, and inter-seasonal variability of total wind-generated waves, wind-seas, and swell waves in the Indian Ocean (IO). The significant wave height (SWH) of ERA-5 was validated with the multi-platform calibrated altimetry wave height. The correlation coefficient of SWH was about 0.97 considering the entire domain, and it is greater than 0.9 for different sectors in the IO basin. The absolute and root mean square errors in different subdomains are observed in the range of 0.16-0.3 m and 0.2-0.37 m, respectively and found higher in the extra tropical IO (ETSI). The ETSI showed an increasing trend for both wind-seas and swell waves (0.5-1 cm/year). In context to wind-seas, shift in the westerly wind belt leads to pole-ward increasing and equator-ward decreasing trend. In the northern Arabian Sea, the swell waves exhibited an increasing trend (0.8 cm/year) during the southwest monsoon. Meanwhile, the wind-sea activity over the Arabian Sea and Head Bay of Bengal are seen to decrease. The regions in the IO that experienced higher variability of SWH in the last four decades are identified using EOF (Empirical Orthogonal Function) analysis. The dominant mode of Principal Component Analysis signified the explicit contribution of swell waves over the total significant wave height. The second and third modes of variability are majorly contributed by wind-seas, especially in the south IO attributed due to the Southern Annular Mode (SAM). The wavelet spectrum analysis conducted at the identified locations of higher variability manifests the domain sensitivity by which the Makran coast experienced an increased average variance in annular and semi-annular scales.