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Upper-ocean mixing due to surface gravity waves
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2015 (English)In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 120, no 12, 8210-8228 p.Article in journal (Refereed) Published
Abstract [en]

Surface gravity waves play an important role in the lower layer of the atmosphere and the upper layer of the ocean. Surface waves effect upper-ocean mixing mainly through four processes: wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by nonbreaking waves. We introduce the impact of these four processes into a 1-D  ocean turbulence model. The parameterizations used are based mainly on existing investigations. Comparison of simulation results and measurements demonstrates that considering all the effects of waves, rather than just one effect, significantly improves model performance. The nonbreaking-wave-induced mixing and Langmuir turbulence are the most important terms when considering the impact of waves on upper-ocean mixing. Under high-wave conditions, the turbulent mixing induced by nonbreaking waves can be of the same order of magnitude as the viscosity induced by other terms at the surface. Nonbreaking waves contribute very little to shear production and their impact is negligible in the models. Sensitivity experiments demonstrate that the vertical profile of the Stokes drift calculated from the 2-D wave spectrum improves model performance significantly compared with other methods of introducing wave effects.

Place, publisher, year, edition, pages
2015. Vol. 120, no 12, 8210-8228 p.
Keyword [en]
ocean mixing; nonbreaking waves; Langmuir circulation; Coriolis-Stokes forcing; breaking waves
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-270913DOI: 10.1002/2015JC011329ISI: 000369153200027OAI: oai:DiVA.org:uu-270913DiVA: diva2:890836
Funder
Swedish Research Council, 2012-3902
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Impact of surface gravity waves on air-sea fluxes and upper-ocean mixing
Open this publication in new window or tab >>Impact of surface gravity waves on air-sea fluxes and upper-ocean mixing
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves play a vital role in the air-sea interaction. They can alter the turbulence ofthe bottom atmospheric layer as well as the upper-ocean layer. Accordingly, they can affect themomentum flux, heat fluxes, as well as the upper-ocean mixing. In most numerical models, waveinfluences are not considered or not fully considered. The wave influences on the atmosphereand the ocean are important for weather forecasts and climate studies. Here, different aspects ofwave impact on the atmosphere and the ocean are introduced into numerical models.In the first study, a wave-state-dependent sea spray generation function and Charnock co-efficient were applied to a wind stress parameterization under high wind speeds. The newlyproposed wind stress parameterization and a sea spray influenced heat flux parameterizationwere applied to an atmosphere-wave coupled model to study their influence on the simulationof mid-latitude storms. The new wind stress parameterization reduces wind speed simulationerror during high wind speed ranges and intensifies the storms. Adding the sea spray impacton heat fluxes improves the model performance concerning the air temperature. Adding the seaspray impact both on the wind stress and heat fluxes results in best model performance in allexperiments for wind speed, and air temperature.In the second study, the influence of surface waves on upper-ocean mixing was parameter-ized into a 1D k − ε ocean turbulence model though four processes (wave breaking, Stokes driftinteraction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves)based mainly on existing investigations. Considering all the effects of surface gravity waves,rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir turbulence are the most important terms when considering theimpact of waves on upper-ocean mixing. Sensitivity experiments demonstrate that vertical pro-files of the Stokes drift calculated from 2D wave spectrum improve the model performancesignificantly compared with other methods of calculating the vertical profiles of the Stokes drift.Introducing the wave influences in modelling systems, the results verified against measure-ments. Concluding from these studies for the further model development, the wave influencesshould be taken into account to improve the model performance.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, Department of Earth Sciences, 2016. 35 p.
National Category
Meteorology and Atmospheric Sciences Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:uu:diva-276466 (URN)
Presentation
2016-02-11, Norrland II, Villavagen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-02-24 Created: 2016-02-13 Last updated: 2016-02-24Bibliographically approved
2. Introducing Surface Gravity Waves into Earth System Models
Open this publication in new window or tab >>Introducing Surface Gravity Waves into Earth System Models
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects.

Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models.

Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence.

Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences.

Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing.

Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 50 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1478
Keyword
Surface gravity waves, Air-sea interaction, Earth-System Model, Atmospheric mixing, Upper-ocean turbulence
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-314760 (URN)978-91-554-9822-1 (ISBN)
Public defence
2017-04-12, Axel Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2017-03-10 Created: 2017-02-06 Last updated: 2017-03-20

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Wu, LichuanRutgersson, AnnaSahlée, Erik

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