Impact of assimilating satellite and in-situ buoy observed significant wave height on a regional wave forecasting system in the Indian Ocean

This paper discusses the upgraded data assimilation (DA) wave forecasting system at the Indian National Centre for Ocean Information Services (INCOIS). Significant wave height (SWH) observations from deep and shallow water buoys in the North Indian Ocean are incorporated into the assimilation system in conjunction with satellite observations from SARAL/AltiKa, Jason-3, Sentinel-3a, and Sentinel-3b. In deep water, satellite DA improved the SWH forecast by similar to 16%, and the inclusion of buoy observations enhanced it up to similar to 43% in the initial forecast hours. The impact of satellite DA persists throughout the forecast period of 5 days for swell height, with 11-27% improvement. Ingestion of buoy observations further improved it up to similar to 31.5% at the 3rd hr forecast. For the wind-sea height, buoy DA resulted in an improvement of 9-26% during the initial 12 hr. In general, the positive impact of buoy DA only lasts till the 30th hr forecast. In shallow water, the impact of satellite DA on SWH prediction is moderate, with positive improvements of 4-7.5%. Adding buoy observations significantly improved it to 10-40% in the initial 12 hr, especially for the low wave heights. Although the buoy DA improved the prediction of wave periods compared to the non-assimilated model, it tends to degrade the forecast compared to the model with satellite DA alone. This points to the limitation of the current assimilation approach in correcting the wave energy distribution in the background spectrum, particularly at higher frequencies.