“Shamal” swells in the Arabian Sea and their influence along the west coast of India

Abstract

Wave data collected off Ratnagiri, Goa and Dwarka along the west coast of India during winter season (NE monsoon and early pre-monsoon) present distinct wave characteristics with periodicity ranging between 2 and 5 days associated with shamal events. The notable wave characteristics during these events are: an increase in wave height, decrease in swell period and a common propagation direction (northwest) for wind sea and swell. IFREMER/CERSAT blended winds clearly show the presence of strong northwesterly winds in the Arabian Peninsula and northwestern Arabian Sea, which are associated with the winter shamal events. The winds during such events generate large northwesterly swells (shamal swells) in the northwestern Arabian Sea and propagate towards the west coast of India in the NW direction with mean periods ranging between 6 and 8 s. Numerical simulations reproduce the shamal swells over the Arabian Sea, and they can be traced all along the west coast of India, however, with lesser order of magnitude from north to south. Generation and propagation of shamal swells and their influence along the west coast of India have been described.