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- Qiao, Wenli, et al.
(author)
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Momentum Flux Balance at the Air-Sea Interface
- 2021
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In: Journal of Geophysical Research - Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 126:2
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Journal article (peer-reviewed)abstract
- Abstract Ocean waves can spatiotemporally redistribute the momentum flux at the air-sea interface, which varies with the sea state. Traditional atmosphere-ocean coupled systems assume the ocean-side stress (Ïoc) to be identical to the air-side stress (Ïa); consequently, the role of ocean waves is neglected. In this study, the wave impacts on the air-sea momentum flux are investigated based on 1-year high-resolution model simulations in the Baltic Sea using an atmosphere-wave coupled model (Uppsala University-Coupled Model, UU-CM). The simulation results show that Ïoc can differ significantly from Ïa in both direction and magnitude. The direction difference between Ïoc and Ïa (DD(Ïoc, Ïa)) and the normalized momentum flux () decrease with increasing inverse wave age. In general, and DD(Ïoc, Ïa) are pronounced under wind-following swell and wind-crossing swell conditions, respectively. The occurrence frequencies of large and DD(Ïoc, Ïa) are higher nearer the coast; statistically, both decrease significantly with increasing water depth because of the joint effect of dissipation processes. Based on four selected areas, we find that alongshore winds (winds blowing parallel to the coastline) are favorable for large angular differences between Ïoc and Ïa (DD(Ïoc, Ïa) > 5°). However, onshore winds predominate at . The Ïa in the wave model is generally less than that obtained from the atmospheric model under low-moderate wind conditions if the wave model feeds only the Charnock coefficient (roughness length) back to the atmospheric model in coupled systems.
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- Chen, Sheng, et al.
(author)
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On the First Observed Wave-Induced Stress Over the Global Ocean
- 2020
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In: Journal of Geophysical Research - Oceans. - : AMER GEOPHYSICAL UNION. - 2169-9275 .- 2169-9291. ; 125:12
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Journal article (peer-reviewed)abstract
- Despite many investigations/studies on the surface wave-induced stress, the global feature of the wave-induced stress has not been obtained previously as that requires a simultaneous observation of wave spectra and wind on a global scale. The China France Oceanography Satellite (CFOSAT) provided an opportunity for the first time to evaluate the global wave-induced stress and its contribution to the total wind stress. In this study, the global spatial distributions of wave-induced stress and its correlated index for August to November in 2019 are presented using the simultaneous ocean surface winds and wave spectra from the CFOSAT. The main results show that the wave-induced stress is fundamentally dependent on the wind and wave fields on a global scale and shows significant temporal and spatial variations. Further analyses indicate that there is an upward momentum flux under strong swells and low wind speeds (below similar to 5 m/s), and an anticorrelation between the dimensionless wave-induced stress and the proportion of swell energy to the total. Finally, the variations of the surface wave induced wind stress are clear asymmetric between northern and southern hemispheres in late summer but symmetric in late fall, which are closely associated with the seasonal changes in large-scale atmospheric circulation.
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- Li, Songlin, et al.
(author)
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Effects of Sea Spray on Extreme Precipitation Forecasting: A Case Study in Beijing of China
- 2024
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 51:15
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Journal article (peer-reviewed)abstract
- This study investigates the effects of sea spray on extreme precipitation forecast in Beijing of China between 28 July and 2 August 2023 as a case test. In this case, fully coupled model increased upward moisture in the Bohai and Yellow Seas and increased accumulated rainfall by 21% in North China. For the extreme precipitation events with the 5-day accumulated precipitation exceeding 500 mm, the atmosphere-only model did not forecast the events; the coupled model without sea spray performed well with the 0.29 threat score (TS) and 88 mm root mean square error (RMSE); in the fully coupled model, the effects of sea spray increased atmospheric instability, which increased the precipitation around Beijing and yielded a more accurate forecast with the 0.37 TS and 65 mm RMSE. This paper suggests a scientific clue to improve numerical simulation for extreme rainfall events, however, more cases are still needed for statistical evaluation.
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- Wang, Gang, et al.
(author)
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Estimating sea spray volume flux with a laser gauge in a self-consistent system
- 2023
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In: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 9
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Journal article (peer-reviewed)abstract
- Sea spray is one of the drivers of heat, mass, and gas exchange between the ocean and the atmosphere, and its volume flux could be estimated by the record of the laser intensity. In the laboratory experiments, the relationship between sea spray and laser intensity could be established since the returned laser intensity of the observing gauge and spray concentration can be observed instantaneously. However, the difficulty to generalize the laboratory result to field observations is that the measurement of sea spray is usually unavailable on the open seas. Recent studies introduced an environment variable (atmospheric extinction coefficient for instance) to relate the laser intensity to spray volume flux for both laboratory and field observations so that the relationship established in the laboratory experiments could be extended to open seas. These studies however gave estimations of great difference since the relationships between each pair of the variables (spray volume flux, laser intensity, and the atmospheric extinction coefficient) are considered separately. This work established a self-consistent system composed of the three variables, in which the relationship between each pair of the variables in the system is consistent with that deduced from their respective relationships with the third variable. Consistency here we means that if Y=f(X), Y=g(Z) and Z=h(X), then Y=g(h(X))=f(X) is expected. The consistency of the relationships ensures that the estimation of the sea spray volume flux from laser intensity is robust. We established self-consistent relationships for the variables in the system composed of laser intensity, environment variable, and sea spray volume flux, for both laboratory and field experiments. Among them, the relationship between wind speed and spray volume flux is a reasonable reflection of the physical properties in two ways: a threshold value of spray volume flux at low wind speeds and the saturation at strong wind speeds. For a uniform regression of wind speed onto spray volume, a dimensionless parameter concerning wind speed is needed.
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- Wu, Lichuan, et al.
(author)
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The Redistribution of Air-Sea Momentum and Turbulent Kinetic Energy Fluxes by Ocean Surface Gravity Waves
- 2022
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In: Journal of Physical Oceanography. - : American Meteorological Society. ; 52:7, s. 1483-1496
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Journal article (peer-reviewed)abstract
- The momentum flux to the ocean interior is commonly assumed to be identical to the momentum flux lost from the atmosphere in traditional atmosphere, ocean, and coupled models. However, ocean surface gravity waves (hereafter waves) can alter the magnitude and direction of the ocean-side stress (tau(oc)) from the air-side stress (tau(a)). This is rarely considered in coupled climate and forecast models. Based on a 30-yr wave hindcast, the redistribution of the global wind stress and turbulent kinetic energy (TKE) flux by waves was investigated. Waves play a more important role in the windy oceans in middle and high latitudes than that in the oceans in the tropics (i.e., the central portion of the Pacific and Atlantic Oceans). On average, the relative difference between tau(oc) and tau(a), gamma(tau), can be up to 6% in middle and high latitudes. The frequency of occurrence of gamma(tau) > 9% can be up to 10% in the windy extratropics. The directional difference between tau(oc) and tau(a) exceeds 3.5 degrees in the middle and high latitudes 10% of the time. The difference between tau(oc) and tau(a) becomes more significant closer to the coasts of the continents due to strong wind gradients. The friction velocity-based approach overestimates (underestimates) the breaking-induced TKE flux in the tropics (middle and high latitudes). The findings presented in the current study show that coupled climate and Earth system models would clearly benefit from the inclusion of a wave model. Significance StatementThe purpose of this study is to investigate the redistribution of the global wind stress and turbulent kinetic energy flux due to surface waves based on a 30-yr wave hindcast. The mean relative difference of the magnitude between the air-side and ocean-side stress is up to 6% with a 90th percentile of more than 9% in the windy extratropics. Due to strong wind gradients, the redistributive role of waves in the stress becomes more significant closer to coasts. The results indicate that we should consider the redistributive role of waves in the momentum and energy fluxes in climate and Earth system models since they are the key elements in the predictability of weather forecasting models and climate models.
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- Wu, Lichuan, et al.
(author)
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Wind Profile in the Wave Boundary Layer and Its Application in a Coupled Atmosphere-Wave Model
- 2022
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In: Journal of Geophysical Research - Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 127:2
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Journal article (peer-reviewed)abstract
- Current models cannot capture well the impacts of wind waves on the atmospheric boundary layer. Here, we proposed a new turbulence closure model to estimate the wind stress in the wave boundary layer from viscous stress, shear-induced turbulent stress, wind-sea induced stress, and swell-induced upward stress separately. The misalignment between the wind stress and wind is also considered in the model. Single-column simulations indicate that (a) the swell-induced upward momentum flux increases the surface wind and changes the wind direction, (b) the misalignment between the upward momentum flux and wind has a more significant impact on the wind profile than that from the downward momentum flux, and (c) the impact of swell-induced upward momentum flux decreases with atmospheric convection. The proposed closure scheme was implemented into an atmosphere-wave coupled model. A month-long simulation over the ocean off California shows that the surface wind can be altered up to 5% by ocean surface gravity waves.Plain Language SummaryAir-sea interactions are important for weather and climate predictions since they control the momentum and energy transfer between the atmosphere and the ocean. In current models, the momentum flux in the atmospheric boundary layer is estimated by turbulence closure models, which were developed heavily based on measurements over land. However, those turbulence closure models often fail to capture the momentum flux and wind profile in the marine atmospheric boundary layer due to wave impacts. In this study, we developed a new turbulence closure model that can capture the impacts of swell-induced upward momentum flux and the misalignment angle between the stress and wind as well as the swell-induced low-level wind jet. A month-long simulation indicates that considering the wave, impacts can alter the surface wind up to 5%. Thus, it is necessary to implement those wave impacts into ocean, weather, and climate models.
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- Zhao, Biao, Dr, et al.
(author)
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A Numerical Study of Tropical Cyclone and Ocean Responses to Air‐Sea Momentum Flux at High Winds
- 2024
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In: Journal of Geophysical Research - Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 129:7
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Journal article (peer-reviewed)abstract
- The relationship between minimum sea level pressure (MSLP) and maximum wind speed, is a commonly employed metric for assessing tropical cyclone (TC) forecast skill. However, accurately reproducing this relationship in TC forecasts is challenging. By introducing a new air-sea momentum flux scheme considering both wave state and saturation (decrease) effect at high winds into a fully coupled atmosphere-ocean-wave model, our numerical results reveal that the maximum wind speed and MSLP respond oppositely to the air-sea momentum flux change. The simulated wind-pressure relationship aligns well with observations when the new flux scheme is used. This study highlights the large sensitivity of wind-pressure relationship to the air-sea momentum flux parameterization at high winds. Furthermore, the air-sea momentum flux has a significant effect on ocean wave characteristics and sea surface temperature (SST) cooling in TC simulations.
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