Reduced drag coefficient for high wind speeds in tropical cyclones

Nature ◽  
2003 ◽  
Vol 422 (6929) ◽  
pp. 279-283 ◽  
Author(s):  
Mark D. Powell ◽  
Peter J. Vickery ◽  
Timothy A. Reinhold
Keyword(s):  
Drag Coefficient ◽  
Tropical Cyclones ◽  
High Wind ◽  
Wind Speeds

scholarly journals Relationship between Sea Surface Drag Coefficient and Wave State

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.

scholarly journals A Review of Parameterizations for Enthalpy and Momentum Fluxes from Sea Spray in Tropical Cyclones

2021 ◽  
Author(s):  
Sydney Sroka ◽  
Kerry Emanuel
Keyword(s):  
Tropical Cyclones ◽  
Critical Role ◽  
Sea Spray ◽  
High Wind ◽  
High Wind Speed ◽  
Wind Speeds ◽  
Crucial Component ◽  
Momentum Fluxes ◽  
Interaction Scheme ◽  
Speed Regime

AbstractThe intensity of tropical cyclones is sensitive to the air-sea fluxes of enthalpy and momentum. Sea spray plays a critical role in mediating enthalpy and momentum fluxes over the ocean’s surface at high wind speeds, and parameterizing the influence of sea spray is a crucial component of any air-sea interaction scheme used for the high wind regime where sea spray is ubiquitous. Many studies have proposed parameterizations of air-sea flux that incorporate the microphysics of sea spray evaporation and the mechanics of sea spray stress. Unfortunately, there is not yet a consensus on which parameterization best represents air-sea exchange in tropical cyclones, and the different proposed parameterizations can yield substantially different tropical cyclone intensities. This paper seeks to review the developments in parameterizations of the sea spray-mediated enthalpy and momentum fluxes for the high wind speed regime and to synthesize key findings that are common across many investigations.

scholarly journals Impact of the Reduced Drag Coefficient on Ocean Wave Modeling under Hurricane Conditions

2008 ◽  
Vol 136 (3) ◽  
pp. 1217-1223 ◽  
Author(s):  
Il-Ju Moon ◽  
Isaac Ginis ◽  
Tetsu Hara
Keyword(s):  
Drag Coefficient ◽  
Hurricane Katrina ◽  
Wind Wave ◽  
Wave Model ◽  
High Wind ◽  
Model Surface ◽  
Wind Speeds ◽  
Tank Experiment ◽  
Wave Heights ◽  
Significant Wave Heights

Abstract Effects of new drag coefficient (Cd) parameterizations on WAVEWATCH III (WW3) model surface wave simulations are investigated. The new parameterizations are based on a coupled wind–wave model (CWW) and a wave tank experiment, and yields reduced Cd at high wind speeds. Numerical experiments for uniform winds and Hurricane Katrina (2005) indicate that the original Cd parameterization used in WW3 overestimates drag at high wind speeds compared to recent observational, theoretical, and numerical modeling results. Comparisons with buoy measurements during Hurricane Katrina demonstrate that WW3 simulations with the new Cd parameterizations yield more accurate significant wave heights compared to simulations with the original Cd parameterization, provided that accurate high-resolution wind forcing fields are used.

scholarly journals Ocean's response to Hurricane Frances and its implications for drag coefficient parameterization at high wind speeds

2009 ◽  
Vol 114 (C4) ◽  
Author(s):  
S. E. Zedler ◽  
P. P. Niiler ◽  
D. Stammer ◽  
E. Terrill ◽  
J. Morzel
Keyword(s):  
Drag Coefficient ◽  
High Wind ◽  
Wind Speeds

scholarly journals Relating Wind and Stress under Tropical Cyclones with Scatterometer

2016 ◽  
Vol 33 (6) ◽  
pp. 1151-1158 ◽  
Author(s):  
W. Timothy Liu ◽  
Wenqing Tang
Keyword(s):  
Drag Coefficient ◽  
Tropical Cyclones ◽  
Turbulent Transport ◽  
Local Stress ◽  
Ocean Surface ◽  
Retrieval Algorithm ◽  
Strong Wind ◽  
Surface Cooling ◽  
Wind Retrieval ◽  
Wind Speeds

AbstractOcean surface stress, the turbulent transport of momentum, is largely derived from wind through a drag coefficient. In tropical cyclones (TCs), scatterometers have difficulty measuring strong wind and there is large uncertainty in the drag coefficient. This study postulates that the microwave backscatter from ocean surface roughness, which is in equilibrium with local stress, does not distinguish between weather systems. The reduced sensitivity of scatterometer wind retrieval algorithms under the strong wind is an air–sea interaction problem that is caused by a change in the behavior of the drag coefficient rather than a sensor problem. Under this assumption, a stress retrieval algorithm developed over a moderate wind range is applied to retrieve stress under the strong winds of TCs. Over a moderate wind range, the abundant wind measurements and the more established drag coefficient value allow for sufficient stress data to be computed from wind to develop a stress retrieval algorithm for the scatterometer. Using 0.9 million coincident stress and wind pairs, the study shows that the drag coefficient decreases with wind speed at a much steeper rate than previously revealed, for wind speeds over 25 m s−1. The result implies that the ocean applies less drag to inhibit TC intensification, and that TCs cause less ocean mixing and surface cooling than previous studies indicated.

The Influence of wave state and sea spray on drag coefficient from low to high wind speeds

2016 ◽  
Vol 15 (1) ◽  
pp. 41-49 ◽  
Author(s):  
Jian Shi ◽  
Zhong Zhong ◽  
Xunqiang Li ◽  
Guorong Jiang ◽  
Wenhua Zeng ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Sea Spray ◽  
High Wind ◽  
Wave State ◽  
Wind Speeds

scholarly journals A Physics-Based Parameterization of Air–Sea Momentum Flux at High Wind Speeds and Its Impact on Hurricane Intensity Predictions

2007 ◽  
Vol 135 (8) ◽  
pp. 2869-2878 ◽  
Author(s):  
Il-Ju Moon ◽  
Isaac Ginis ◽  
Tetsu Hara ◽  
Biju Thomas
Keyword(s):  
Drag Coefficient ◽  
Momentum Flux ◽  
Surface Wind ◽  
Wind Pressure ◽  
Central Pressure ◽  
Geophysical Fluid Dynamics Laboratory ◽  
High Wind ◽  
Wind Speeds ◽  
Gfdl Model ◽  
The Impact

Abstract A new bulk parameterization of the air–sea momentum flux at high wind speeds is proposed based on coupled wave–wind model simulations for 10 tropical cyclones that occurred in the Atlantic Ocean during 1998–2003. The new parameterization describes how the roughness length increases linearly with wind speed and the neutral drag coefficient tends to level off at high wind speeds. The proposed parameterization is then tested on real hurricanes using the operational Geophysical Fluid Dynamics Laboratory (GFDL) coupled hurricane–ocean prediction model. The impact of the new parameterization on the hurricane prediction is mainly found in increased maximum surface wind speeds, while it does not appreciably affect the hurricane central pressure prediction. This helps to improve the GFDL model–predicted wind–pressure relationship in strong hurricanes. Attempts are made to provide physical explanations as to why the reduced drag coefficient affects surface wind speeds but not the central pressure in hurricanes.

scholarly journals Laboratory Measurements of Heat Transfer and Drag Coefficients at Extremely High Wind Speeds

2018 ◽  
Vol 48 (4) ◽  
pp. 959-974 ◽  
Author(s):  
Satoru Komori ◽  
Koji Iwano ◽  
Naohisa Takagaki ◽  
Ryo Onishi ◽  
Ryoichi Kurose ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Tropical Cyclones ◽  
High Speed ◽  
Analytic Model ◽  
Sensible Heat ◽  
High Wind ◽  
Transfer Coefficients ◽  
Drag Coefficients ◽  
Wind Speeds ◽  
Heat Transfer Coefficients

AbstractHeat and momentum transfer across the wind-driven breaking air–water interface at extremely high wind speeds was experimentally investigated using a high-speed wind-wave tank. An original multi-heat-balance method was utilized to directly measure latent and sensible heat transfer coefficients. The results show that both heat transfer coefficients level off at low and normal wind speeds but increase sharply at extremely high wind speeds. The coefficients have a similar shape for wind speeds at a height of 10 m. Therefore, the wind speed dependence on the latent and sensible heat transfer coefficients can be represented by that of the enthalpy coefficient even in the extremely high-speed region. To show how significantly the drag and enthalpy coefficients affect the intensity of tropical cyclones, the coefficients were applied to Emanuel’s analytic model. The analytic model shows that the difference between the present laboratory and conventional correlations significantly affects the maximum storm intensity predictions, and the present laboratory enthalpy and drag coefficients have the remarkable effect on intensity promotion at extremely high wind speeds. In addition, the simulations of strong tropical cyclones using the Weather Research and Forecasting (WRF) Model with the present and conventional correlations are shown for reference in the appendix. The results obtained from the models suggest that it is of great importance to propose more reliable correlations, verified not only by laboratory but also by field experiments at extremely high wind speeds.

scholarly journals Dependence of Power Characteristics on Savonius Rotor Segmentation

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2912
Author(s):  
Krzysztof Doerffer ◽  
Janusz Telega ◽  
Piotr Doerffer ◽  
Paulina Hercel ◽  
Andrzej Tomporowski
Keyword(s):  
High Wind ◽  
Horizontal Axis Wind Turbine ◽  
Savonius Rotor ◽  
Power Characteristics ◽  
Wind Speeds ◽  
Single Segment ◽  
High Elongation ◽  
Low Wind Speeds ◽  
Number Of Segments ◽  
Rotor Type

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.

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