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Introducing Surface Gravity Waves into Earth System Models
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
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. , p. 50
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1478
Keyword [en]
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: urn:nbn:se:uu:diva-314760ISBN: 978-91-554-9822-1 (print)OAI: oai:DiVA.org:uu-314760DiVA, id: diva2:1071650
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
List of papers
1. Surface Wave Impact When Simulating Midlatitude Storm Development
Open this publication in new window or tab >>Surface Wave Impact When Simulating Midlatitude Storm Development
2017 (English)In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 34, no 1, p. 233-248Article in journal, News item (Refereed) Published
Abstract [en]

Surface gravity waves, present at the air–sea interface, can affect the momentum flux and heat fluxes by modifying turbulence in the lower layers of the atmosphere. How to incorporate wave impacts into model parameterizations is still an open issue. In this study, the influence of a dynamic roughness length (considering instantaneous wave-induced stress), horizontal resolution, and the coupling time resolution between waves and the atmosphere on storm simulations are investigated using sensitivity experiments. Based on the sim- ulations of six midlatitude storms using both an atmosphere–wave coupled model and an atmospheric stand- alone model, the impacts are investigated. Adding the wave-induced stress weakens the storm intensity. Applying a roughness length tuned to an average friction velocity is not enough to capture the simulation results from ‘‘true’’ wave-related roughness length. High-horizontal-resolution models intensify the simula- tion of storms, which is valid for both coupled and uncoupled models. Compared with the atmospheric stand- alone model, the coupled model (considering the influence of dynamic roughness length) is more sensitive to the model horizontal resolution. During reasonable ranges, the coupling time resolution does not have a significant impact on the storm intensity based on the limited experiments used in this study. It is concluded that the dynamic wave influence (instantaneous wave influence) and the model resolution should be taken into account during the development of forecast and climate models.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-313154 (URN)10.1175/JTECH-D-16-0070.1 (DOI)000391826300016 ()
Funder
Swedish Research Council, 2012-3902
Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2017-11-29Bibliographically approved
2. 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, article id 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
3. Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere-wave model
Open this publication in new window or tab >>Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere-wave model
2016 (English)In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 121, no 7, p. 4633-4648Article in journal (Refereed) Published
Abstract [en]

Over the ocean, the atmospheric turbulence can be significantly affected by swell waves. Change in the atmospheric turbulence affects the wind stress and atmospheric mixing over swell waves. In this study, the influence of swell on atmospheric mixing and wind stress is introduced into an atmosphere-wave-coupled regional climate model, separately and combined. The swell influence on atmospheric mixing is introduced into the atmospheric mixing length formula by adding a swell-induced contribution to the mixing. The swell influence on the wind stress under wind-following swell, moderate-range wind, and near-neutral and unstable stratification conditions is introduced by changing the roughness length. Five year simulation results indicate that adding the swell influence on atmospheric mixing has limited influence, only slightly increasing the near-surface wind speed; in contrast, adding the swell influence on wind stress reduces the near-surface wind speed. Introducing the wave influence roughness length has a larger influence than does adding the swell influence on mixing. Compared with measurements, adding the swell influence on both atmospheric mixing and wind stress gives the best model performance for the wind speed. The influence varies with wave characteristics for different sea basins. Swell occurs infrequently in the studied area, and one could expect more influence in high-swell-frequency areas (i.e., low-latitude ocean). We conclude that the influence of swell on atmospheric mixing and wind stress should be considered when developing climate models.

Keyword
air-sea interaction; swell waves; wind stress; atmospheric mixing
National Category
Oceanography, Hydrology and Water Resources Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-302007 (URN)10.1002/2015JC011576 (DOI)000383468500013 ()
Funder
Swedish Research Council, 2012-3902
Available from: 2016-08-27 Created: 2016-08-27 Last updated: 2018-01-10Bibliographically approved
4. Atmospheric boundary layer turbulence closure scheme for wind-following swell conditions
Open this publication in new window or tab >>Atmospheric boundary layer turbulence closure scheme for wind-following swell conditions
2017 (English)In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 74, no 7, p. 2363-2382Article in journal (Refereed) Published
Abstract [en]

Over the ocean, atmospheric boundary layer turbulence can be altered by underlying waves. Under swell conditions, the impact of waves on the atmosphere is more complicated compared to that under wind-wave conditions. Based on large-eddy simulation (LES), the wind-following swell impact on the atmospheric boundary layer is investigated through three terms: swell-induced surface momentum flux, the vertical profile of swell-induced momentum flux, and the swell impact on atmospheric mixing. The swell-induced surface momentum flux displays a decreasing trend with increasing atmospheric convection. The swell-induced momentum flux decays approximately exponentially with height. Compared with atmospheric convection, the decay coefficient is more sensitive to wave age. Atmospheric mixing is enhanced under swell conditions relative to a flat stationary surface. The swell impact on the atmospheric boundary layer is incorporated into a turbulence closure parameterization through the three terms. The modified turbulence closure parameterization is introduced into a single-column atmospheric model to simulate LES cases. Adding only the swell impact on the atmospheric mixing has a limited influence on wind profiles. Adding both the impact of swell on the atmospheric mixing and the profile of swell-induced momentum flux significantly improves the agreement between the 1D atmospheric simulation results and the LES results, to some extent simulating the wave-induced low-level wind jet. It is concluded that the swell impact should be included in atmospheric numerical models.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-314757 (URN)10.1175/JAS-D-16-0308.1 (DOI)000405556700015 ()
Funder
Swedish Research Council, 2012-3902
Available from: 2017-02-06 Created: 2017-02-06 Last updated: 2017-10-24Bibliographically approved
5. 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, p. 8210-8228Article 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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