scholarly journals Wind Speed and Stability Effects on Coupling between Surface Wind Stress and SST Observed from Buoys and Satellite

2012 ◽  
Vol 25 (5) ◽  
pp. 1544-1569 ◽  
Author(s):  
Larry W. O’Neill
Keyword(s):  
Stress Response ◽  
Wind Speed ◽  
Wind Stress ◽  
Stress Responses ◽  
Gulf Stream ◽  
Surface Wind ◽  
Equatorial Pacific ◽  
Satellite Observations ◽  
Actual Surface ◽  
Surface Wind Stress

The surface wind and stress responses to sea surface temperature (SST) are examined using collocated moored buoy and satellite observations in the Gulf Stream and the eastern equatorial Pacific. Using 17 buoy pairs, differences in the wind speed, 10-m equivalent neutral wind speed (ENW), and surface wind stress magnitude between two buoys separated by between 150 and 350 km were all found to be highly correlated to, and satisfy linear relations with, the SST difference on time scales longer than 10 days. This wind–SST coupling is consistent with previous analyses of spatially high-pass-filtered satellite ENW and SST fields. For all buoy pairs, the ENW and wind speed responses to SST differ by only 10%–30%, indicating that the ENW and stress responses to SST are attributable primarily to the response of the actual surface wind speed to SST rather than to stability. This result clarifies the dynamical pathway of the wind–SST coupling on the oceanic mesoscale. This buoy-pair methodology is used further to evaluate the ENW–SST coupling derived from collocated satellite observations of ENW by the Quick Scatterometer (QuikSCAT) and SST by the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) on board the Aqua satellite. Overall, the satellite and buoy ENW responses to SST compare well, with normalized mean differences (satellite minus buoy) of 17% over the Gulf Stream and −31% and 2% over the southern and northern sides of the equatorial Pacific, respectively. Finally, seasonal variability of the large-scale ENW is shown to modulate the wind stress response to SST, whereby stronger winter wind enhances the stress response by a factor of ~2 relative to the ENW response.

scholarly journals Wavelet Analyses of Turbulence in the Hurricane Surface Layer during Landfalls

2010 ◽  
Vol 67 (12) ◽  
pp. 3793-3805 ◽  
Author(s):  
Ping Zhu ◽  
Jun A. Zhang ◽  
Forrest J. Masters
Keyword(s):  
Surface Layer ◽  
Wind Speed ◽  
Wind Stress ◽  
Surface Wind ◽  
Power Spectra ◽  
Substantial Effect ◽  
Vertical Transport ◽  
Transport Processes ◽  
Wind Speeds ◽  
Surface Wind Stress

Abstract Using wavelet transform (WT), this study analyzes the surface wind data collected by the portable wind towers during the landfalls of six hurricanes and one tropical storm in the 2002–04 seasons. The WT, which decomposes a time series onto the scale-time domain, provides a means to investigate the role of turbulent eddies in the vertical transport in the unsteady, inhomogeneous hurricane surface layer. The normalized WT power spectra (NWPS) show that the hurricane boundary layer roll vortices tend to suppress the eddy circulations immediately adjacent to rolls, but they do not appear to have a substantial effect on eddies smaller than 100 m. For low-wind conditions with surface wind speeds less than 10 m s−1, the contributions of small eddies (<236 m) to the surface wind stress and turbulent kinetic energy (TKE) decrease with the increase of wind speed. The opposite variation trend is found for eddies greater than 236 m. However, for wind speeds greater than 10 m s−1, contributions of both small and large eddies tend to level off as wind speeds keep increasing. It is also found that the scale of the peak NWPS of the surface wind stress is nearly constant with a mean value of approximately 86 m, whereas the scale of the peak NWPS of TKE generally increases with the increase of wind speed, suggesting the different roles of eddies in generating fluxes and TKE. This study illustrates the unique characteristics of the surface layer turbulent structures during hurricane landfalls. It is hoped that the findings of this study could enlighten the development and improvement of turbulent mixing schemes so that the vertical transport processes in the hurricane surface layer can be appropriately parameterized in forecasting models.

scholarly journals Whitecap and Wind Stress Observations by Microwave Radiometers: Global Coverage and Extreme Conditions

2019 ◽  
Vol 49 (9) ◽  
pp. 2291-2307 ◽  
Author(s):  
Paul A. Hwang ◽  
Nicolas Reul ◽  
Thomas Meissner ◽  
Simon H. Yueh
Keyword(s):  
Surface Wave ◽  
Wind Speed ◽  
Wind Stress ◽  
Thermal Emission ◽  
Microwave Radiometer ◽  
Wave Spectrum ◽  
Surface Wind ◽  
Unit Surface Area ◽  
Whitecap Coverage ◽  
Surface Wind Stress

AbstractWhitecaps manifest surface wave breaking that impacts many ocean processes, of which surface wind stress is the driving force. For close to a half century of quantitative whitecap reporting, only a small number of observations are obtained under conditions with wind speed exceeding 25 m s−1. Whitecap contribution is a critical component of ocean surface microwave thermal emission. In the forward solution of microwave thermal emission, the input forcing parameter is wind speed, which is used to generate the modeled surface wind stress, surface wave spectrum, and whitecap coverage necessary for the subsequent electromagnetic (EM) computation. In this respect, microwave radiometer data can be used to evaluate various formulations of the drag coefficient, whitecap coverage, and surface wave spectrum. In reverse, whitecap coverage and surface wind stress can be retrieved from microwave radiometer data by employing precalculated solutions of an analytical microwave thermal emission model that yields good agreement with field measurements. There are many published microwave radiometer datasets covering a wide range of frequency, incidence angle, and both vertical and horizontal polarizations, with maximum wind speed exceeding 90 m s−1. These datasets provide information of whitecap coverage and surface wind stress from global oceans and in extreme wind conditions. Breaking wave energy dissipation rate per unit surface area can be estimated also by making use of its linear relationship with whitecap coverage derived from earlier studies.

An Assessment of the Sea Surface Temperature Influence on Surface Wind Stress in Numerical Weather Prediction and Climate Models

2006 ◽  
Vol 19 (12) ◽  
pp. 2743-2762 ◽  
Author(s):  
Eric D. Maloney ◽  
Dudley B. Chelton
Keyword(s):  
Wind Stress ◽  
Climate Models ◽  
Spatial Scales ◽  
Weather Prediction ◽  
Surface Wind ◽  
Satellite Observations ◽  
Grid Resolution ◽  
Coupling Coefficients ◽  
Surface Wind Stress ◽  
Current Systems

Abstract The ability of six climate models to capture the observed coupling between SST and surface wind stress in the vicinity of strong midlatitude SST fronts is analyzed. The analysis emphasizes air–sea interactions associated with ocean meanders in the eastward extensions of major western boundary current systems such as the Gulf Stream, Kuroshio, and Agulhas Current. Satellite observations of wind stress from the SeaWinds scatterometer on NASA’s Quick Scatterometer and SST from the Advanced Microwave Scanning Radiometer clearly indicate the influence of SST on surface wind stress on scales smaller than about 30° longitude × 10° latitude. Spatially high-pass-filtered SST and wind stress variations are linearly related, with higher SST associated with higher wind stress. The influence of SST on wind stress is also clearly identifiable in the ECMWF operational forecast model, having a grid resolution of 0.35° × 0.35° (T511). However, the coupling coefficient between wind stress and SST, as indicated by the slope of the linear least squares fit, is only half as strong as for satellite observations. The ability to simulate realistic air–sea interactions is present to varying degrees in the coupled climate models examined. The Model for Interdisciplinary Research on Climate 3.2 (MIROC3.2) high-resolution version (HIRES) (1.1° × 1.1°, T106) and the NCAR Community Climate System Model 3.0 (1.4° × 1.4°, T85) are the highest-resolution models considered and produce the most realistic air–sea coupling associated with midlatitude current systems. Coupling coefficients between SST and wind stress in MIROC3.2_HIRES and the NCAR model are at least comparable to those in the ECMWF operational model. The spatial scales of midlatitude SST variations and SST-induced wind perturbations in MIROC3.2_HIRES are comparable to those of satellite observations. The spatial scales of SST variability in the NCAR model are larger than those in the ECMWF model and satellite observations, and hence the spatial scales of SST-induced perturbations in the wind fields are larger. It is found that the ability of climate models to simulate air–sea interactions degrades with decreasing grid resolution. SST anomalies in the GFDL Climate Model 2.0 (CM2.0) (2.0° × 2.5°), Met Office Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) (2.5° × 3.8°), and MIROC3.2 medium-resolution version (MEDRES) (2.8° × 2.8°, T42) have larger spatial scales and are more geographically confined than in the higher-resolution models. The GISS Model E20/Russell (4.0° × 5.0°) is unable to resolve the midlatitude ocean eddies that produce prominent air–sea interaction. Notably, MIROC3.2_MEDRES exhibits much weaker coupling between wind stress and SST than does the higher vertical and horizontal resolution version of the same model. GFDL CM2.0 and Met Office HadCM3 exhibit a linear relationship between SST and wind stress. However, coupling coefficients for the Met Office model are significantly weaker than in the GFDL and higher-resolution models. In addition to model grid resolution (both vertical and horizontal), deficiencies in the parameterization of boundary layer processes may be responsible for some of these differences in air–sea coupling between models and observations.

scholarly journals Effects of spatial scale modification on the responses of surface wind stress to the thermal front in the northern South China Sea

2021 ◽  
pp. 1-44
Author(s):  
Rui Shi ◽  
Xinyu Guo ◽  
Ju Chen ◽  
LiLi Zeng ◽  
Bo Wu ◽  
...  
Keyword(s):  
South China Sea ◽  
Wind Stress ◽  
South China ◽  
Northern South China Sea ◽  
Surface Wind ◽  
Reanalysis Data ◽  
Satellite Observations ◽  
Surface Wind Stress ◽  
Linear Relationships ◽  
Sst Gradient

AbstractThe responses of surface wind stress to the mesoscale sea surface temperature (SST) anomalies associated with the SST front in the northern South China Sea (NSCS) are studied using satellite observations and reanalysis data. Both satellite and reanalysis data explicitly show the linear relationships between the spatial-high-pass filtered wind stress perturbation derivatives and the underlying SST gradient field. However, the noise in the linear relationships is much smaller in the reanalysis data than in the satellite observations. This result is rarely reported in other frontal areas.The wavelet analysis shows that the satellite scatterometer observed numerous high wavenumber perturbations within 100 km in the NSCS, but these perturbations were absent in the reanalysis data. The linear relationship between the perturbation SST gradient and derivative wind stress fields is not significant at this scale, which enhances the noise in the linear relationship. The spatial bandpass-filtered perturbation between 100 km and 300 km can give reasonable estimates of the coupling coefficients between the wind stress divergence and downwind SST gradient (αd) and between the wind stress curl and crosswind SST gradient (αc) in the NSCS, with values of 1.33 × 10−2 N m−2 per °C and 0.95 × 10−2 N m−2 per °C, respectively.

scholarly journals Wind Stress Curl and Coastal Upwelling in the Area of Monterey Bay Observed during AOSN-II

2011 ◽  
Vol 41 (5) ◽  
pp. 857-877 ◽  
Author(s):  
Q. Wang ◽  
J. A. Kalogiros ◽  
S. R. Ramp ◽  
J. D. Paduan ◽  
G. Buzorius ◽  
...  
Keyword(s):  
Wind Speed ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Surface Wind ◽  
Sea Surface ◽  
Monterey Bay ◽  
Surface Currents ◽  
Surface Wind Stress

Abstract Aircraft measurements obtained during the 2003–04 Autonomous Ocean Sampling Network (AOSN-II) project were used to study the effect of small-scale variations of near-surface wind stress on coastal upwelling in the area of Monterey Bay. Using 5-km-long measurement segments at 35 m above the sea surface, wind stress and its curl were calculated with estimated accuracy of 0.02–0.03 N m−2 and 0.1–0.2 N m−2 per 100 kilometers, respectively. The spatial distribution of wind speed, wind stress, stress curl, and sea surface temperature were analyzed for four general wind conditions: northerly or southerly wind along the coastline, onshore flow, and offshore flow. Wind stress and speed maxima frequently were found to be noncollocated as bulk parameterizations imply owing to significant stability and nonhomogeneity effects at cold SST pools. The analyses revealed that complicated processes with different time scales (wind stress field variation, ocean response and upwelling, sea surface currents, and heating by solar radiation) affect the coastal sea surface temperature. It was found that the stress-curl-induced coastal upwelling only dominates in events during which positive curl extended systematically over a significant area (scales larger than 20 km). These events included cases with a northerly wind, which resulted in an expansion fan downstream from Point Año Nuevo (wind speed peaks greater than about 8–10 m s−1), and cases with an offshore/onshore flow, which are characterized by weak background upwelling due to Ekman transport. However, in general, observations show that cold pools of sea surface temperature in the central area of Monterey Bay were advected by ocean surface currents from strong upwelling regions. Aircraft vertical soundings taken in the bay area showed that dominant effects of the lee wave sheltering of coastal mountains resulted in weak atmospheric turbulence and affected the development of the atmospheric boundary layer. This effect causes low wind stress that limits upwelling, especially at the northern part of Monterey Bay. The sea surface temperature is generally warm in this part of the bay because of the shallow oceanic surface layer and solar heating of the upper ocean.

FEATURES OF WIND FIELD OVER THE SEA SURFACE IN THE COASTAL AREA BASED ON SAR OBSERVATIONS

2017 ◽  
Author(s):  
Anna Monzikova ◽  
Anna Monzikova ◽  
Vladimir Kudryavtsev Vladimir ◽  
Vladimir Kudryavtsev Vladimir ◽  
Alexander Myasoedov ◽  
...  
Keyword(s):  
Wind Stress ◽  
Surface Wind ◽  
Quantitative Description ◽  
Energy Resource ◽  
Resource Assessment ◽  
Internal Boundary Layer ◽  
Offshore Wind ◽  
Internal Boundary ◽  
Sar Images ◽  
Surface Wind Stress

“Wind-shadowing” effects in the Gulf of Finland coastal zone are analyzed using high resolution Envisat Synthetic Aperture Radar (SAR) measurements and model simulations. These effects are related to the internal boundary layer (IBL) development due to abrupt change the surface roughness at the sea-land boundary. Inside the "shadow" areas the airflow accelerates and the surface wind stress increases with the fetch. Such features can be revealed in SAR images as dark areas adjacent to the coastal line. Quantitative description of these effects is important for offshore wind energy resource assessment. It is found that the surface wind stress scaled by its equilibrium value (far from the coast) is universal functions of the dimensionless fetch Xf/G. Wind stress reaches an equilibrium value at the distance Xf/G of about 0.4.

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