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Wave height analysis from 10 years of observations in the Norwegian Sea

Wave height analysis from 10 years of observations in the Norwegian Sea
Wave height analysis from 10 years of observations in the Norwegian Sea
Large waves pose risks to ships, offshore structures, coastal infrastructure and ecosystems. This paper analyses 10 years of in-situ measurements of significant wave height (Hs) and maximum wave height (Hmax) from the ocean weather ship Polarfront in the Norwegian Sea. During the period 2000 to 2009, surface elevation was recorded every 0.59 s during sampling periods of 30 min.

The Hmax observations scale linearly with Hs on average. A widely-used empirical Weibull distribution is found to estimate average values of Hmax/Hs and Hmax better than a Rayleigh distribution, but tends to underestimate both for all but the smallest waves. In this paper we propose a modified Rayleigh distribution which compensates for the heterogeneity of the observed dataset: the distribution is fitted to the whole dataset and improves the estimate of the largest waves. Over the 10-year period, the Weibull distribution approximates the observed Hs and Hmax well, and an exponential function can be used to predict the probability distribution function of the ratio Hmax/Hs. However, the Weibull distribution tends to underestimate the occurrence of extremely large values of Hs and Hmax.

The persistence of Hs and Hmax in winter is also examined. Wave fields with Hs>12 m and Hmax>16 m do not last longer than 3 h. Low-to-moderate wave heights that persist for more than 12 h dominate the relationship of the wave field with the winter NAO index over 2000–2009. In contrast, the inter-annual variability of wave fields with Hs>5.5 m or Hmax>8.5 m and wave fields persisting over ~2.5 days is not associated with the winter NAO index.
Wave statistics, Persistence, SBWR, NAO, Norwegian Sea
0278-4343
47-56
Feng, Xiangbo
ea69bf52-760a-46a1-921c-b3ebf172c754
Tsimplis, Michael
df6dd749-cda4-46ec-983c-bf022d737031
Quartly, G.D.
3d1e4e87-f001-4d18-b95f-9bca4db6ff9d
Yelland, M. J.
3b2e2a38-334f-430f-b110-253a0a835a07
Feng, Xiangbo
ea69bf52-760a-46a1-921c-b3ebf172c754
Tsimplis, Michael
df6dd749-cda4-46ec-983c-bf022d737031
Quartly, G.D.
3d1e4e87-f001-4d18-b95f-9bca4db6ff9d
Yelland, M. J.
3b2e2a38-334f-430f-b110-253a0a835a07

Feng, Xiangbo, Tsimplis, Michael, Quartly, G.D. and Yelland, M. J. (2014) Wave height analysis from 10 years of observations in the Norwegian Sea. Continental Shelf Research, 72, 47-56. (doi:10.1016/j.csr.2013.10.013).

Record type: Article

Abstract

Large waves pose risks to ships, offshore structures, coastal infrastructure and ecosystems. This paper analyses 10 years of in-situ measurements of significant wave height (Hs) and maximum wave height (Hmax) from the ocean weather ship Polarfront in the Norwegian Sea. During the period 2000 to 2009, surface elevation was recorded every 0.59 s during sampling periods of 30 min.

The Hmax observations scale linearly with Hs on average. A widely-used empirical Weibull distribution is found to estimate average values of Hmax/Hs and Hmax better than a Rayleigh distribution, but tends to underestimate both for all but the smallest waves. In this paper we propose a modified Rayleigh distribution which compensates for the heterogeneity of the observed dataset: the distribution is fitted to the whole dataset and improves the estimate of the largest waves. Over the 10-year period, the Weibull distribution approximates the observed Hs and Hmax well, and an exponential function can be used to predict the probability distribution function of the ratio Hmax/Hs. However, the Weibull distribution tends to underestimate the occurrence of extremely large values of Hs and Hmax.

The persistence of Hs and Hmax in winter is also examined. Wave fields with Hs>12 m and Hmax>16 m do not last longer than 3 h. Low-to-moderate wave heights that persist for more than 12 h dominate the relationship of the wave field with the winter NAO index over 2000–2009. In contrast, the inter-annual variability of wave fields with Hs>5.5 m or Hmax>8.5 m and wave fields persisting over ~2.5 days is not associated with the winter NAO index.

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Published date: 1 January 2014
Keywords: Wave statistics, Persistence, SBWR, NAO, Norwegian Sea
Organisations: Ocean and Earth Science

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Local EPrints ID: 360891
URI: http://eprints.soton.ac.uk/id/eprint/360891
ISSN: 0278-4343
PURE UUID: 31bc53ad-7f5a-4828-87a1-c98057b39d6d

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Date deposited: 06 Jan 2014 13:09
Last modified: 25 Nov 2019 20:44

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Contributors

Author: Xiangbo Feng
Author: Michael Tsimplis
Author: G.D. Quartly
Author: M. J. Yelland

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