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अमूर्त

Wave Hindcasting Using WAM and WAVEWATCH III: A Comparison Study Utilizing Oceansat-2 (OSCAT) Winds

Swain J, Umesh PA, Balchand AN, B. Prasad Kumar

In this study, the state-of-the-art third generation wave models WAM and WAVEWATCH-III (WWIII) have been used to predict waves for the North Indian Ocean over 1°× 1° (lat × long) grid resolutions utilizing six-hourly processed winds which was possible with the launch of OCEANSAT-2 (OSCAT) by ISRO, on 23 September 2009. The study demonstrates the application of interpolated OSCAT winds to hindcast waves across the globe using two deep-water models WAM and WAVEWATCH III (WWIII) and to compare the skill of the models using error analysis. In this context, the wave models WAM and WWIII were forced using OSCAT winds for the year 2011 over the global domain as well as for the North Indian Ocean (regional domain) using appropriate boundary conditions/inputs. The output from the models such as significant wave height (Hs) and mean wave period (Tc) were validated with an NDBC buoy measurement during January to December 2011 in the North Atlantic Ocean and for few selected buoys in the Bay of Bengal for the month of July 2011 (peak southwest monsoon). The comparisons of OSCAT winds with NDBC wind measurements reveal that the overall trend and dominant directions are consistent with the observational data. The validation of significant wave parameters of the selected buoy in the North Atlantic ocean revealed very high correlation (R>0.9) with percentage error <20% for Hs and Tc. The comparisons between the observed and predicted wave parameters in the Bay of Bengal showed that percentage error ranged between 9 to 24% for Hs and within 10% for Tc. It is noted that WAM describes the variability of wave heights realistically with smaller error estimates and better correlation coefficients than WWIII. Such validation studies are proven to be useful in quantifying the performance of these wave models which are being utilized or yet to be further explored for routine operational applications as well as for long-term wave hindcasting in the strategic areas of importance in deep as well as shallow waters by nesting with suitable near-shore models in the littoral zone.