Drag Coefficient and Its Sea State Dependence under Tropical Cyclones

Zhou, Xiangxian; Hara, Tetsu; Ginis, Isaac; D’Asaro, Eric A.; Hsu, Je‐Yuan; Reichl, Brandon G.

doi:10.1175/jpo-d-21-0246.1

Cited by 11 publications

(52 citation statements)

References 36 publications

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“…This is supported by our data, which shows that COARE's wave dependent parameterization overestimates C D for alongshore wind and does not better predict observations than parameterization without waves (Figures 3 and 4). Similarly, Zhou et al (2022) found that, at high wind speeds, C D is significantly reduced when misalignment between the wind and dominant wave directions exceeds 45°. It is convictable that the complex wave systems created by tropical cyclones (e.g., Collins et al, 2018) can result in slanting-fetch like conditions limiting C D in some regions which will impact storm intensity.…”

Section: Results In Relation To Previous Researchmentioning

confidence: 76%

“…Similarly, Zhou et al. (2022) found that, at high wind speeds, C D is significantly reduced when misalignment between the wind and dominant wave directions exceeds 45°. It is convictable that the complex wave systems created by tropical cyclones (e.g., Collins et al., 2018) can result in slanting‐fetch like conditions limiting C D in some regions which will impact storm intensity.…”

Section: Discussionmentioning

confidence: 76%

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Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

2022

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Open‐ocean homogeneity is violated in the near shore region by wave shoaling and breaking, varying wind‐swell incidence angles, complex currents patterns, rapid bathymetric changes, and shore‐side topographic features. Consequently, existing drag coefficient parameterizations, which were largely developed in deep water, are not effective. This has an adverse impact on marine forecasts, weather and climate models, and coastal morphology prediction. There exists a critical need to identify and systematically quantify the impact of coastal processes and features on the momentum flux over a wide range of wind speeds. As part of the DUring Nearshore Event eXperiment at the Field Research Facility in Duck, NC, six months of direct flux observations were collected from a tower at the end of a 560 m pier. These were used to study the variability of the aerodynamic drag coefficient. Results show that for winds above 3 m s−1 the drag coefficient was between 15% and 50% higher for onshore winds when compared to alongshore. This is attributed to more energy in the downwind component of the flux around the dominant wave frequency for onshore winds, and is independent of wind speed. Holistically, the Coupled Ocean Atmosphere Response Experiment (COARE) algorithm over predicts the drag coefficient for shoaling waves. When separated by wind direction, COARE best predicts the drag coefficient for onshore winds. The results of this study can help the development of more robust nearshore momentum flux parameterizations. This will ultimately lead to improved weather and climate forecasting in the littoral zone, and more physically realistic short‐ and long‐term coastal resilience strategies.

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Section: Results In Relation To Previous Researchmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 76%

Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

2022

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“…The uncertainty of wind stress is due to two factors: uncertainty of wind speed, and uncertainty of the drag coefficient. Zhou et al (2022) estimated the wind stress by matching the upper ocean current observations (from the EM-APEX floats) and model simulations under the same 5 TCs as in this study. They then estimated the mean drag coefficient based on a particular wind speed product (URI wind in Zhou et al (2022)) and the estimated wind stress.…”

Section: Wind Fieldsmentioning

confidence: 99%

“…Thus without addition information on C d , simulations of the upper ocean response to a particular storm may have significant errors in air-sea momentum flux. Following Sanford et al (2011) and Hsu et al (2017), Zhou et al (2022) have estimated the wind stress and drag coefficient by combining ocean current observations under 5 TCs and coupled ocean-wave model simulations. On the right to rear-right side of the storm, where wind and waves are aligned, the average C d ranges between 2.0 × 10 −3 and 3.0 × 10 −3 , and the stress is close to the downwind direction.…”

mentioning

confidence: 99%

Evidence of Langmuir Mixing Effects in the Upper Ocean Layer During Tropical Cyclones Using Observations and a Coupled Wave‐Ocean Model

Zhou,

Hara,

Ginis

et al. 2023

JGR Oceans

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Mixing of the ocean beneath tropical cyclones (TC) cools the surface temperature thereby modifying the storm intensity. Modeling studies predict that surface wave forcing through Langmuir turbulence (LT) increases the mixing and cooling and decreases near‐surface vertical velocity shear. However, there are very few quantitative observational validations of these model predictions, and the validation efforts are often limited by uncertainties in the drag coefficient (Cd). We combine EM‐APEX and Lagrangian float measurements of temperature, salinity, velocity, and vertical turbulent kinetic energy (VKE) from five TCs with a coupled ocean‐wave model (Modular Ocean Model 6—WAVEWATCH III) forced by the drag coefficient Cd directly constrained for these storms. On the right‐hand of the storms in the northern hemisphere, where wind and waves are nearly aligned, the measured VKE is consistent with predictions of models including LT and 2–3 times higher than predictions without LT. Similarly, vertical shear in the upper 20 m is small, consistent with predictions of LT models and inconsistent with the large shears predicted by models without LT. On the left‐hand of the storms, where wind and waves are misaligned, the observed VKE and cooling are reduced compared to those on the right‐hand, consistent with the measured decrease in Cd. These results confirm the importance of surface waves for ocean cooling and thus TC intensity, through both Cd and LT effects. However, the model predictions, even with the LT parameterization, underestimate the upper ocean cooling and mixed layer deepening by 20%–30%, suggesting possible deficiency of the existing LT parameterization.

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“…We also note that we will compute the wind frictional velocity u * from 10‐m wind speed ( U 10 ) using the COARE3.5 drag coefficient (Edson et al., 2013). The drag coefficient itself could also be parameterized as a function of the sea state (making the non‐breaking transfer velocity also a sea‐state dependent term), but we choose to not consider this effect here to simplify our analysis and due to remaining uncertainty in the sea state dependence of drag coefficients (e.g., Sauvage et al., 2023; Zhou et al., 2022), in particular in high wind speed conditions, or mixed seas conditions.…”

Section: Gas Transfer Velocity Modelmentioning

confidence: 99%

A Sea State Dependent Gas Transfer Velocity for CO₂ Unifying Theory, Model, and Field Data

Zhou,

Reichl,

Romero

et al. 2023

Earth and Space Science

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Wave breaking induced bubbles contribute a significant part of air‐sea gas fluxes. Recent modeling of the sea state dependent CO2 flux found that bubbles contribute up to ∼40% of the total CO2 air‐sea fluxes (Reichl & Deike, 2020, https://doi.org/10.1029/2020gl087267). In this study, we implement the sea state dependent bubble gas transfer formulation of Deike and Melville (2018, https://doi.org/10.1029/2018gl078758) into a spectral wave model (WAVEWATCH III) incorporating the spectral modeling of the wave breaking distribution from Romero (2019, https://doi.org/10.1029/2019gl083408). We evaluate the accuracy of the sea state dependent gas transfer parameterization against available measurements of CO2 gas transfer velocity from 9 data sets (11 research cruises, see Yang et al. (2022, https://doi.org/10.3389/fmars.2022.826421)). The sea state dependent parameterization for CO2 gas transfer velocity is consistent with observations, while the traditional wind‐only parameterization used in most global models slightly underestimates the observations of gas transfer velocity. We produce a climatology of the sea state dependent gas transfer velocity using reanalysis wind and wave data spanning 1980–2017. The climatology shows that the enhanced gas transfer velocity occurs frequently in regions with developed sea states (with strong wave breaking and high significant wave height). The present study provides a general sea state dependent parameterization for gas transfer, which can be implemented in global coupled models.

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Drag Coefficient and Its Sea State Dependence under Tropical Cyclones

Cited by 11 publications

References 36 publications

Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

Evidence of Langmuir Mixing Effects in the Upper Ocean Layer During Tropical Cyclones Using Observations and a Coupled Wave‐Ocean Model

A Sea State Dependent Gas Transfer Velocity for CO₂ Unifying Theory, Model, and Field Data

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Drag Coefficient and Its Sea State Dependence under Tropical Cyclones

Cited by 11 publications

References 36 publications

Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

Pier‐Based Measurements of Air‐Sea Momentum Fluxes Over Shoaling Waves During DUNEX

Evidence of Langmuir Mixing Effects in the Upper Ocean Layer During Tropical Cyclones Using Observations and a Coupled Wave‐Ocean Model

A Sea State Dependent Gas Transfer Velocity for CO2 Unifying Theory, Model, and Field Data

Contact Info

Product

Resources

About

A Sea State Dependent Gas Transfer Velocity for CO₂ Unifying Theory, Model, and Field Data