Freak waves off Ratnagiri, west coast of India

Abstract

<span style="font-size:11.0pt;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-bidi-font-family:mangal;="" mso-ansi-language:en-in;mso-fareast-language:en-us;mso-bidi-language:hi;="" mso-no-proof:yes"="">Freak <span style="font-size:11.0pt;mso-fareast-font-family: " times="" new="" roman";mso-bidi-font-family:mangal;background:white;mso-ansi-language:="" en-in;mso-fareast-language:en-us;mso-bidi-language:hi;font-style:normal"="">waves<span style="font-size:11.0pt;font-family:" times="" new="" roman";mso-fareast-font-family:="" "times="" roman";mso-bidi-font-family:mangal;background:white;mso-ansi-language:="" en-in;mso-fareast-language:en-us;mso-bidi-language:hi"=""> are relatively large and spontaneous ocean surface gravity waves whose heights are larger than the expected maximum wave height for a given sea state. <span style="font-size:11.0pt;font-family:" times="" new="" roman";mso-fareast-font-family:="" "times="" roman";mso-bidi-font-family:mangal;mso-ansi-language:en-in;="" mso-fareast-language:en-us;mso-bidi-language:hi"="">Wave data collected off Ratnagiri, along the west coast of India during <span style="font-size:11.0pt; mso-fareast-font-family:" times="" new="" roman";background:white;mso-ansi-language:="" en-in;mso-fareast-language:en-us;mso-bidi-language:hi"="">1 January to 31 December 2011<span style="font-size:11.0pt;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-bidi-font-family:mangal;="" mso-ansi-language:en-in;mso-fareast-language:en-us;mso-bidi-language:hi"=""> using directional wave rider buoy at 13 m water depth is used to study the freak waves. Abnormality Index (AI), the ratio between maximum wave height and significant wave height, is used to identify and study the variation of the freak wave events off Ratnagiri. From the half hourly wave data covering one year period, 89 freak wave events are observed. The statistics built on these selected events suggests that maximum freak events (29 events) are during the rough SW monsoon and 20 events during the calm pre-monsoon season. Highest freak wave (wave height=6.9 m) is observed in July 2011. The Abnormality Index varied from 2 to 2.5 during the study period. Daily variations in number of freak wave events are associated with the interaction between sea-breeze generated random wind sea and swells propagating towards the study area.</span></span></span></span></span></span>