Impact on Sea-Surface Electromagnetic Scattering and Emission Modeling of Recent Progress on the Parameterization of Ocean Surface Roughness, Drag Coefficient, and Whitecap Coverage in High Wind Conditions

AbstractOcean surface roughness and whitecaps are driven by the ocean surface wind stress; thus, their values calculated from the wind speed input may vary significantly depending on the drag coefficient formula applied. Because roughness and whitecaps are critical elements of the ocean surface response in microwave remote sensing, the extensive microwave remote sensing measurements contain the information of the drag coefficient, surface roughness, and whitecap coverage. The scattering radar cross sections from global measurements under calm to tropical cyclone conditions have been used effectively to improve the formulation of the surface roughness spectrum. In this paper, the microwave radiometer measurements in tropical cyclones are exploited to extract information of the drag coefficient and whitecap coverage in high winds. The results show that when expressed as a wind speed power function, the exponent in high winds (greater than about 35 m s−1) is about −1 for the drag coefficient, 0.5 for the wind friction velocity, and 1.25 for the whitecap coverage.

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A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam

Journal of Marine Science and Engineering ◽

10.3390/jmse9030246 ◽

2021 ◽

Vol 9 (3) ◽

pp. 246

Author(s):

Difu Sun ◽

Junqiang Song ◽

Xiaoyong Li ◽

Kaijun Ren ◽

Hongze Leng

Keyword(s):

Surface Roughness ◽

Wind Speed ◽

Drag Coefficient ◽

Sea Surface ◽

High Wind Speed ◽

Wave State ◽

Wind Speeds ◽

Sea Surface Roughness ◽

Extreme Wind ◽

The Impact

A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.

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Relationship between Sea Surface Drag Coefficient and Wave State

Journal of Marine Science and Engineering ◽

10.3390/jmse9111248 ◽

2021 ◽

Vol 9 (11) ◽

pp. 1248

Author(s):

Jian Shi ◽

Zhihao Feng ◽

Yuan Sun ◽

Xueyan Zhang ◽

Wenjing Zhang ◽

...

Keyword(s):

Drag Coefficient ◽

Momentum Flux ◽

Sea Surface ◽

Sea Spray ◽

Wave Age ◽

High Wind ◽

Surface Drag ◽

Wave State ◽

Wind Speeds ◽

Strong Winds

The sea surface drag coefficient plays an important role in momentum transmission between the atmosphere and the ocean, which is affected by ocean waves. The total air–sea momentum flux consists of effective momentum flux and sea spray momentum flux. Sea spray momentum flux involves sea surface drag, which is largely affected by the ocean wave state. Under strong winds, the sea surface drag coefficient (CD) does not increase linearly with the increasing wind speed, namely, the increase of CD is inhibited by strong winds. In this study, a sea surface drag coefficient is constructed that can be applied to the calculation of the air–sea momentum flux under high wind speed. The sea surface drag coefficient also considers the influence of wave state and sea spray droplets generated by wave breaking. Specially, the wave-dependent sea spray generation function is employed to calculate sea spray momentum flux. This facilitates the analysis not only on the sensitivity of the sea spray momentum flux to wave age, but also on the effect of wave state on the effective CD (CD, eff) under strong winds. Our results indicate that wave age plays an important role in determining CD. When the wave age is >0.4, CD decreases with the wave age. However, when the wave age is ≤0.4, CD increases with the wave age at low and moderate wind speeds but tends to decrease with the wave age at high wind speeds.

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Experimental Study of High Wind Sea Surface Drag Coefficient

Morskoy gidrofizicheskiy zhurnal ◽

10.22449/0233-7584-2015-1-53-63 ◽

2015 ◽

Cited By ~ 1

Author(s):

I.A. Repina ◽

A.Yu. Artamonov ◽

M.I. Varentsov ◽

A.V. Kozyrev ◽

◽

...

Keyword(s):

Experimental Study ◽

Drag Coefficient ◽

Sea Surface ◽

High Wind ◽

Surface Drag ◽

Wind Sea

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Ocean Surface Roughness Spectrum in High Wind Condition for Microwave Backscatter and Emission Computations*

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-12-00239.1 ◽

2013 ◽

Vol 30 (9) ◽

pp. 2168-2188 ◽

Cited By ~ 40

Author(s):

Paul A. Hwang ◽

Derek M. Burrage ◽

David W. Wang ◽

Joel C. Wesson

Keyword(s):

Remote Sensing ◽

Surface Roughness ◽

Surface Waves ◽

Microwave Remote Sensing ◽

Ocean Surface ◽

Short Wave ◽

Wind Condition ◽

Bragg Resonance ◽

High Wind ◽

Radar Backscatter

Abstract Ocean surface roughness plays an important role in air–sea interaction and ocean remote sensing. Its primary contribution is from surface waves much shorter than the energetic wave components near the peak of the wave energy spectrum. Field measurements of short-scale waves are scarce. In contrast, microwave remote sensing has produced a large volume of data useful for short-wave investigation. Particularly, Bragg resonance is the primary mechanism of radar backscatter from the ocean surface and the radar serves as a spectrometer of short surface waves. The roughness spectra inverted from radar backscatter measurements expand the short-wave database to high wind conditions in which in situ sensors do not function well. Using scatterometer geophysical model functions for L-, C-, and Ku-band microwave frequencies, the inverted roughness spectra, covering Bragg resonance wavelengths from 0.012 to 0.20 m, show a convergent trend in high winds. This convergent trend is incorporated in the surface roughness spectrum model to improve the applicable wind speed range for microwave scattering and emission computations.

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Recent Development of Drag Coefficient, Foam, and Surface Roughness for High Wind EM Emission and Scattering Computation

IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium ◽

10.1109/igarss.2019.8899020 ◽

2019 ◽

Cited By ~ 1

Author(s):

Paul A. Hwang

Keyword(s):

Surface Roughness ◽

Drag Coefficient ◽

High Wind

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Influence of Wave State and Sea Spray on the Roughness Length: Feedback on Medicanes

Atmosphere ◽

10.3390/atmos9080301 ◽

2018 ◽

Vol 9 (8) ◽

pp. 301 ◽

Cited By ~ 13

Author(s):

Umberto Rizza ◽

Elisa Canepa ◽

Antonio Ricchi ◽

Davide Bonaldo ◽

Sandro Carniel ◽

...

Keyword(s):

Surface Roughness ◽

Single Case ◽

Wind Waves ◽

Wave Model ◽

Atmospheric Model ◽

Sea Surface ◽

Sea Spray ◽

High Wind ◽

Wave State ◽

Sea Surface Roughness

Occasionally, storms that share many features with tropical cyclones, including the presence of a quasi-circular “eye” a warm core and strong winds, are observed in the Mediterranean. Generally, they are known as Medicanes, or tropical-like cyclones (TLC). Due to the intense wind forcings and the consequent development of high wind waves, a large number of sea spray droplets—both from bubble bursting and spume tearing processes—are likely to be produced at the sea surface. In order to take into account this process, we implemented an additional Sea Spray Source Function (SSSF) in WRF-Chem, model version 3.6.1, using the GOCART (Goddard Chemistry Aerosol Radiation and Transport) aerosol sectional module. Traditionally, air-sea momentum fluxes are computed through the classical Charnock relation that does not consider the wave-state and sea spray effects on the sea surface roughness explicitly. In order to take into account these forcing, we implemented a more recent parameterization of the sea surface aerodynamic roughness within the WRF surface layer model, which may be applicable to both moderate and high wind conditions. The implemented SSSF and sea surface roughness parameterization have been tested using an operative model sequence based on COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) and WRF-Chem. The third-generation wave model SWAN (Simulating Waves Nearshore), two-way coupled with the WRF atmospheric model in the COAWST framework, provided wave field parameters. Numerical simulations have been integrated with the WRF-Chem chemistry package, with the aim of calculating the sea spray generated by the waves and to include its effect in the Charnock roughness parametrization together with the sea state effect. A single case study is performed, considering the Medicane that affected south-eastern Italy on 26 September 2006. Since this Medicane is one of the most deeply analysed in literature, its investigation can easily shed some light on the feedbacks between sea spray and drag coefficients.

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