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Introducing surface waves in a coupled wave-atmosphere regional climate model: Impact on atmospheric mixing length
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (Meteorologi, AWEP)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (Meteorologi, AWEP)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (awep)
2012 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, C00J15- p.Article in journal (Refereed) Published
Abstract [en]

The marine atmospheric boundary layer is strongly influenced by the moving surface in the presence of surface waves; the impact depends on the wave conditions and the interaction with the atmosphere. Previous studies using measurements as well as numerical simulations with large-eddy simulations have shown that surface waves propagating faster than the wind (swell) alter the surface exchange as well as turbulence properties in the atmosphere. This impact is here introduced in a coupled wave-atmosphere regional climate model with a so-called E − l turbulence scheme (where E is the turbulent kinetic energy and l is a mixing length). A wave age dependent coefficient (here called Wmix) is added to the mixing length in the turbulence parameterization. This acts similarly to inducing additional convection, with larger mixing length and increased eddy diffusivity, when we have near neutral stratification and strong swell. For shallow boundary layers the regional coupled climate model shows a larger response to the introduced wave coupling with increased near surface wind speed and smaller wind gradient between the surface and middle part of the boundary layer. The impact for the studied areas is relatively minor for parameters averaged over 1 year, but for limited periods and specific situations the impact is larger. One could expect a larger impact in areas with stronger swell dominance. We thus conclude that the impact of swell waves on the mixing in the boundary layer is not insignificant and should be taken into account when developing wave-atmosphere coupled regional climate models or global climate models.

Place, publisher, year, edition, pages
2012. Vol. 117, C00J15- p.
Keyword [en]
boundary layer height, regional climate model, surface waves, turbulent mixing, wave-atmosphere coupling
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:uu:diva-173771DOI: 10.1029/2012JC007940ISI: 000305155400001OAI: oai:DiVA.org:uu-173771DiVA: diva2:525109
Available from: 2012-05-05 Created: 2012-05-05 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Fluxes and Mixing Processes in the Marine Atmospheric Boundary Layer
Open this publication in new window or tab >>Fluxes and Mixing Processes in the Marine Atmospheric Boundary Layer
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atmospheric models are strongly dependent on the turbulent exchange of momentum, sensible heat and moisture (latent heat) at the surface. Oceans cover about 70% of the Earth’s surface and understanding the processes that control air-sea exchange is of great importance in order to predict weather and climate. In the atmosphere, for instance, hurricane development, cyclone intensity and track depend on these processes.

Ocean waves constitute an obvious example of air-sea interaction and can cause the air-flow over sea to depend on surface conditions in uniquely different ways compared to boundary layers over land. When waves are generated by wind they are called wind sea or growing sea, and when they leave their generation area or propagate faster than the generating wind they are called swell. The air-sea exchange is mediated by turbulent eddies occurring on many different scales. Field measurements and high-resolution turbulence resolving numerical simulations have here been used to study these processes.

The standard method to measure turbulent fluxes is the eddy covariance method. A spatial separation is often used between instruments when measuring scalar flux; this causes an error which was investigated for the first time over sea. The error is typically smaller over ocean than over land, possibly indicating changes in turbulence structure over sea.

Established and extended analysis methods to determine the dominant scales of momentum transfer was used to interpret how reduced drag and sometimes net upward momentum flux can persist in the boundary layer indirectly affected by swell. A changed turbulence structure with increased turbulence length scales and more effective mixing was found for swell.

A study, using a coupled wave-atmosphere regional climate model, gave a first indication on what impact wave mixing have on atmosphere and wave parameters. Near surface wind speed and wind gradients was affected especially for shallow boundary layers, which typically increased in height from the introduced wave-mixing. A large impact may be expected in regions of the world with predominant swell. The impact of swell waves on air-sea exchange and mixing should be taken into account to develop more reliable coupled Earth system models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 51 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1024
Keyword
Waves, Growing sea, Swell, Marine boundary layer, Air-sea interaction, Mixing, Momentum flux, Wind stress, Flux attenuation, Sensor separation, Large eddy simulation, Multiresolution analysis, Coupling, Wave model, Climate model, Wave age
National Category
Meteorology and Atmospheric Sciences Climate Research
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-195875 (URN)978-91-554-8606-8 (ISBN)
Public defence
2013-04-19, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2013-03-25 Created: 2013-02-28 Last updated: 2013-04-02Bibliographically approved

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Rutgersson, AnnaNilsson, Erik

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