Observations of long-period waves in the nearshore waters of central west coast of India during the fall inter-monsoon period

2017

Ocean Sci.

Self Cite

Abstract. An understanding of the wave spectral shapes is of primary importance for the design of marine facilities. In this paper, the wave spectra collected from January 2011 to December 2015 in the coastal waters of the eastern Arabian Sea using the moored directional waverider buoy are examined to determine the temporal variations in the wave spectral shape. Over an annual cycle for 31.15 % of the time, the peak frequency is between 0.08 and 0.10 Hz; the significant wave height is also relatively high ( ∼ 1.55 m) for waves in this class. The slope of the high-frequency tail of the monthly average wave spectra is high during the Indian summer monsoon period (June-September) compared to other months, and it increases with an increase in significant wave height. There is not much interannual variation in the slope for swell-dominated spectra during the monsoon, while in the non-monsoon period when wind-seas have a high level of influence, the slope varies significantly. Since the exponent of the high-frequency part of the wave spectrum is within the range of −4 to −3 during the monsoon period, the Donelan spectrum shows a better fit for the high-frequency part of the wave spectra in monsoon months compared to other months.

Section: Wave Spectrummentioning

confidence: 99%

Section: Wave Spectrummentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Wave spectral shapes in the coastal waters based on measured data off Karwar on the western coast of India

Nair

2017

Ocean Sci.

Self Cite

“…The long-period waves cause problems for navigation and offshore operations, and induce large motion on moorings (McComb et al, 2009); hence, it is necessary to know the occurrence of long-period waves at a location. Recently, many studies identified long-period waves in the eastern Arabian Sea (Sanil Kumar et al, 2012;Glejin et al, 2016;Amrutha et al, 2017). Sanil Kumar et al (2003) observed that, in the Indian waters, the wave energy spectra contain multiple peaks for about 60 % of the year and when the signifi- cant wave height (H m0 ) is higher than 2 m, they are generally single-peaked.…”

Section: Introductionmentioning

confidence: 99%

“…The multi-peaked wave spectra observed in the coastal region of India are largely dominated by swells (Sanil Kumar et al, 2003). Most of the studies in the Indian waters are in the eastern Arabian Sea (Sanil Kumar et al, 2003Kumar et al, , 2012Glejin et al, 2016;Amrutha et al, 2017;Anjali Nair and Sanil Kumar, 2017) and the western Bay of Bengal (Sundar, 1986;Nayak et al, 2013;Patra and Bhaskaran, 2016). The studies on waves in Indian waters based on measured wave data covering 1 year and above are presented in Table 1.…”

Section: Introductionmentioning

confidence: 99%

Observation of dominance of swells over wind seas in the coastal waters of the Gulf of Mannar, India

Amrutha

2017

Ocean Sci.

Abstract. Wind seas typically dominate over swell seas in coastal gulfs. Waves measured at a location having a water depth of 12 m in the near-shore waters of the Gulf of Mannar during a 1-year period (1 May 2015 to 30 April 2016) are used to examine the predominance of wind seas and swells through spectral characterization. The study shows that even though the location is in a gulf, the annual average value ( ∼ 0.84 m) of the significant wave height in this area is comparable to that along the coastal waters of the Indian subcontinent, but the annual maximum value (∼ 1.7 m) recorded is much less than that (3 to 5 m) observed in those regions. Also, large seasonal variations are not observed in the wave height. The waves of the study region are under the control of sea breeze, with the maximum in the late evening hours and the minimum in the early morning hours. A 5 % increase in the forcing wind field during the monsoon period improved the comparison statistics between the model wave height and the measured values. A total of 53 % of the surface height variance in the study area is a result of swells from the southeast and south, and the remainder are wind seas from the east and southeast.

Climatology and trends of the Indian Ocean surface waves based on 39‐year long ERA5 reanalysis data

Naseef

Intl Journal of Climatology

2019

In this study, the wind and the surface waves in the Indian Ocean (IO) during 1979–2017 are studied based on the ECMWF ERA5 Reanalysis data. Long‐term statistical analysis of extreme waves is carried out based on Generalized Extreme Value distribution using annual maxima and the spatial distribution of return levels for 50 and 100 years are studied. In general, the ERA5 significant wave height (Hs) and maximum wave height (Hmax) show a good agreement with measured buoy data in the coastal (bias ~0.29 m) and deep waters (bias ~0.18 m). During the tropical cyclone, underestimation of Hs and Hmax in the ERA5 data compared to buoy data is 2.7 and 1.4%, but in general the bias is large (~0.69 m). Swell domination is observed in larger regions of the IO, whereas wind‐seas are comparable to swells in the Southern Ocean. The meridional wind speed largely influences the spatial pattern of Hs in the North IO. The stronger winds over the Southern Ocean play a major role in generating higher waves at higher latitudes. Maximum value of the 100‐year return level for Hs in IO is 17.8 m, whereas highest value of the Hs is 16.7 m and Hmax is 32.0 m. Severe wave events are common at 50°–60°S and only during 25% of the time in a year, Hmax is less than 5 m in this region. Ratio of the Hmax to Hs varies from 1.46 to 2.3 with a mean value of 1.87. The 100‐year return value of Hs changed by −4 to 5 m, when the length of the dataset is decreased from 39 years (1979–2017) to recent 20 years. On an average, from 1979 to 2017, the annual average Hmax increased by 0.73 cm/year. In major areas of the IO, a clear decrease of the Hs is observed during 1991–2017, whereas during 1979–2017, an increase in Hs is found.