Wave modelling for the north Indian Ocean using MSMR analysed winds

NCMRWF (National Centre for Medium Range Weather Forecast) winds assimilated with MSMR (Multi-channel Scanning Microwave Radiometer) winds are used as input to MIKE21 Offshore Spectral Wave model (OSW) which takes into account wind induced wave growth, non-linear wave-wave interaction, wave breaking, bottom friction and wave refraction. The model domain covers the north Indian Ocean, bounded by Equator to 30°N and 50° to 100° E. An experiment has been conducted to find out improvement in wave prediction when NCMRWF winds blended with MSMR winds are utilised in the wave model. A comparison between buoy and TOPEX wave heights of May 2000 at 4 buoy locations provides a good match, showing the merit of using altimeter data, wherever it is difficult to obtain measured data for comparison with model wave heights. This is further confirmed when model wave heights for January 2001 in the entire model domain was compared with TOPEX altimeter data a good match for the full range of wave heights considered. Model wave heights, periods and directions have been compared with the data of deep and shallow water buoys. The correlation coefficients  between model and measured wave heights are in the range of 0.85 to 0.91. The model slightly overpredicts wave periods, but match is reasonably good. In general, model wave periods are of the order of 6-9 s during June-July 2001 and 4-8 s during May, August and September 2001. The wave periods clearly indicate that waves during June September are generated by monsoon wind forcing, and dominated by ‘wind waves’.