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

Abstract

Abstract. An attempt has been made to understand the coexistence of wind seas and swells along the west coast of India during non-monsoon season. Wave data were collected in different years during non-monsoon season (off Goa during May 2005, off Ratnagiri during January-February 2008 and off Dwarka during December 2007-January 2008), which is fairly a calm weather season along these regions. Diurnal variation in wave parameters is noticeable along the central west coast of India (off Goa and Ratnagiri), which is due to the interaction of multidirectional waves (both wind seas and swells) of varying magnitudes and frequencies. 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 these 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 weakly present and found to co-exist with the swells almost all the time during non-monsoon season. Wind sea growth has been found while the swell propagates opposite to the direction of the wind and wind sea. 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.

Performance Assessment of ERA5 Wave Data in a Swell Dominated Region

“…During these events, there is a sharp increase in wave height that may exceed 3.5 m in the northwestern Arabian Sea and 1.0-2.0 m along the west coast of India. Although south swells from the Indian Ocean are always present along the west coast of India, Shamal events are the main contributor to the sea states [31].…”

Recent Studies on Wind Seas and Swells in the Indian Ocean: A Review

“…Identification and separation of wind sea and swell energies from the measured spectra allow us to have a more realistic description of the sea state (Wang and Hwang, 2001). The wind sea and swell parameters can be separated using the methodology given by Gilhousen and Hervey (2001), which is based on the wave steepness algorithm (Rashmi et al, 2013). It is observed that during late premonsoon season, swells are dominant (54 % and 71 % at 25 m and 15 m water depths off Goa, respectively) ( Table 1).…”

“…However, when wind seas dominate, mixed seas also increase as the waves are still in the developing stage. (Rashmi et al, 2013).…”

Development of a bi-modal directional wave spectrum

“…Measured wave data in Chabahar bay in the northern coasts of Gulf of Oman are used to verify the proposed approach. The area is experiencing both wind-sea and swell regimes throughout the year especially in Monsoon seasons (Rashmi et al, 2013). As the border of Indian Ocean and Gulf of Oman, it is under construction and development activities and its field observations are recently released.…”