Directional characteristics of waves in the nearshore waters of the eastern Arabian Sea

Abstract

Directional characteristics of the waves at a coastal location in the eastern Arabian Sea are studied based on the data measured from April 2008 to December 2020. The multiple-scale variations; daily, monthly, intraseasonal, seasonal, and interannual; in the directional characteristics are examined. The variations in mean wave direction (Dp), and peak wave period (Tp) during monsoon, pre- and post-monsoon are inspected. The study also investigates the influence of cyclones on Dp. Annually 97.9 % of the time, the waves measured at 9 m water depth fall in intermediate water depth. Waves are predominantly swells, and short-period waves are more during January-March. The waves during monsoon are mainly from 240° to 270°. During the pre-monsoon, a frequent occurrence of multiple waves originating from the northwest, characterised by a relatively short-period (Tp<8 s) is noted. The Tp and Dp collectively exhibit a distinctive tri-modal sea-swell configuration. Waves of low frequency, ∼0.05 Hz, with a direction spanning 180°-210°, are more prominent during the post-monsoon. Since Dp varied significantly (∼175°) in a day, it is vital to take the observations at hourly intervals while researching coastal dynamics. The directional spread of waves at primary peak (27°) is much less than that at the secondary (37°) peak.