Co-existence of wind seas and swells along the west coast of India during non-monsoon season

Wave data collected along the west coast of India (off Goa, Ratnagiri and Dwarka) during non-monsoon season have been analysed to study the co-existence of wind seas and swells. Diurnal variation in wind and wave parameters is noticeable along the central west coast of India (off Goa and Ratnagiri), and this is not present along the northwest coast of India (off Dwarka). Swells are predominantly mature (91%) and old (88%) during late pre-monsoon and post-monsoon seasons, respectively. Sea Swell Energy Ratio quantifies wind sea, swell and mixed seas prevailing in the regions during non-monsoon season. Intermodal Distance (ID) between the energy peaks is moderately separated during non-monsoon season, whereas, during the shamal events, energy peaks are very close to each other (ID ~ 0). However, pure wind seas (ID ~ 1) are found to co-exist with the swells during non-monsoon season. Wind seas are growing, when wind and wind seas are opposite to swell direction. Wind seas have minimum angular spreads in multimodal state. Under low winds, the interaction between wind sea and swell dominates and thereby the multimodal state reduces to unimodal state. The fetch available for the evolution of the wind sea spectrum has been estimated, and it is found to be less than 150 km. For the fetch limited condition, a non-dimensional empirical relation has been derived relating the significant wind sea height in terms of wind speed and peak wind sea period, and this relation fits for the west coast of India.