Inter-annual variations in wave spectral characteristics at a location off the central west coast of India

V Sanil Kumar,M Anjali Nair

doi:10.5194/angeo-33-159-2015

Abstract

Abstract. The inter-annual variations in wave spectrum are examined based on the wave data measured at 9 m water depth off the central west coast of India from 2009 to 2012 using a wave rider buoy. The temporal variation of the spectral energy density over a calendar year indicates similar variation in all the four years studied. The inter-annual variations in wave spectrum are observed in all months with larger variations during January to February, May and October to November due to the changes in wind-sea. The seasonal average wave spectrum during the monsoon (June–September) is single-peaked and the swell component is high in 2011 compared to other years. The annual averaged wave spectrum had higher peak energy during 2011 due to the higher spectral energy present during the monsoon period. During the non-monsoon period, two peaks are predominantly observed in the wave spectra; with the average peak at 0.07 Hz corresponding to the swells from the Indian Ocean and another at 0.17 Hz due to the local wind field.

Highlights

Surface waves generated by winds are of importance for scientific and practical use
The time series plot of the maximum spectral energy density over a calendar year indicates that the spectral energy density is high (5–37 m2 Hz−1) during the monsoon period (June–September) due to the persistence of strong southwest (SW) winds in the Arabian Sea as a result of the SW monsoon (Fig. 2)
The spectral energy density is relatively high during 2011 SW monsoon compared to other years

Summary

Introduction

The sea state is often described in the frequency domain by a wave spectrum. Several studies have shown that combined wind-wave and swell systems can occur both in the open ocean and in coastal areas (Soares, 1991). The earlier studies indicate that the wave spectra in the eastern Arabian Sea are bimodal due to the presence of wind-seas and swells (Baba et al, 1989; Kumar et al, 2000, 2003, 2014; Kumar and Kumar, 2008; Vethamony et al, 2011). Some studies based on satellite derived data have indicated that globally the mean wind speed and the wave height are increasing (Young et al, 2011). It is important to know the inter-annual variations in wave spectra based on the measured data

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