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Impact of surface gravity waves on air-sea fluxes and upper-ocean mixing
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
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: urn:nbn:se:uu:diva-276466OAI: oai:DiVA.org:uu-276466DiVA: diva2:903099
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
List of papers
1. The impact of waves and sea spray on modelling storm track and development
Open this publication in new window or tab >>The impact of waves and sea spray on modelling storm track and development
2015 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 67, 27967Article in journal (Refereed) Published
Abstract [en]

In high wind speed conditions, sea spray generated by intensely breaking waves greatly influences the wind stress and heat fluxes. Measurements indicate that the drag coefficient decreases at high wind speeds. The sea spray generation function (SSGF), an important term of wind stress parameterisation at high wind speeds, is usually treated as a function of wind speed/friction velocity. In this study, we introduce a wave-state-dependent SSGF and wave-age-dependent Charnock number into a high wind speed–wind stress parameterisation. The newly proposed wind stress parameterisation and sea spray heat flux parameterisation were applied to an atmosphere–wave coupled model to study the mid-latitude storm development of six storm cases. Compared with measurements from the FINO1 platform in the North Sea, the new wind stress parameterisation can reduce wind speed simulation errors in the high wind speed range. Considering only sea spray impact on wind stress (and not on heat fluxes) will intensify the storms (in terms of minimum sea level pressure and maximum wind speed), but has little effect on the storm tracks. Considering the impact of sea spray on heat fluxes only (not on wind stress) can improve the model performance regarding air temperature, but it has little effect on the storm intensity and storm track performance. If the impact of sea spray on both the wind stress and heat fluxes is taken into account, the model performs best in all experiments for minimum sea level pressure, maximum wind speed and air temperature.

Keyword
sea spray, wind stress, heat fluxes, storms
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-263091 (URN)10.3402/tellusa.v67.27967 (DOI)000361746300001 ()
Funder
Swedish Research Council
Available from: 2015-09-25 Created: 2015-09-25 Last updated: 2017-12-01Bibliographically approved
2. Upper-ocean mixing due to surface gravity waves
Open this publication in new window or tab >>Upper-ocean mixing due to surface gravity waves
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.

Keyword
ocean mixing; nonbreaking waves; Langmuir circulation; Coriolis-Stokes forcing; breaking waves
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-270913 (URN)10.1002/2015JC011329 (DOI)000369153200027 ()
Funder
Swedish Research Council, 2012-3902
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2017-12-01Bibliographically approved

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