Journal cover Journal topic
Ocean Science An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/os-2017-77
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
19 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).
In situ observations of infragravity wave directionality at nearshore coastal sites
Takehiko Nose1, Alexander Babanin2, and Kevin Ewans3 1Faculty of Science, Engineering, and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122 Australia
2Department of Infrastructure Engineering | Melbourne School of Engineering, The University of Melbourne, Victoria 3010 Australia
3MetOcean Research Ltd, New Plymouth, 4310 New Zealand
Abstract. Infragravity waves is a term used to collectively describe surface gravity waves with periods arbitrarily between 30 and 300 s. In situ observations of infragravity waves at nearshore sites are scarce, and the directionality of the wave field has not received much attention in the past. This paper details a systematic directional analysis of experimental infragravity wave data. Through applying conventional and new directional analysis methods, qualitative and some quantitative characteristics of infragravity wave directions have been resolved. The analysis has found that infragravity waves have a bimodal directional structure with the dominant energy distributed in the propagation sector incident to the coast. It has also been demonstrated that mean infragravity wave directions can be derived, and there is evidence that the directional spreading of infragravity waves is correlated to their wind-generated wave counterparts. Using a numerical model, the qualitative findings were verified; however, contrary to the observations, the dominant direction of the modelled infragravity waves are in the propagation sector outward from the coast. The results provide improved insights into the directionality of infragravity waves, but the disparity between the dominant directions in the model and observations remains to be resolved.

Citation: Nose, T., Babanin, A., and Ewans, K.: In situ observations of infragravity wave directionality at nearshore coastal sites, Ocean Sci. Discuss., https://doi.org/10.5194/os-2017-77, in review, 2017.
Takehiko Nose et al.
Takehiko Nose et al.
Takehiko Nose et al.

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Short summary
Using in situ measurements, we have obtained improved insights into infragravity (IG) wave heights' correlation with the wind waves, which are the forcing of IG waves. We have derived the qualitative directionality of IG wave field, also using in situ observations, and the qualitative physics were verified utilising an IG wave model. IG wave directionality has not had much attention in the past, but the results show that directional characteristics should be considered to study this wave.
Using in situ measurements, we have obtained improved insights into infragravity (IG) wave...
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