wind stress

As hurricanes continue to threaten coastal communities, accurate storm surge forecasting remains a global priority. Achieving a reliable storm surge prediction necessitates accurate hurricane intensity and wind field information. The wind field must be converted to wind stress, which represents the air-sea momentum flux component required in storm surge and other oceanic models. This conversion requires a multiplicative drag coefficient for the air density and wind speed to represent the air-sea momentum exchange at a given location. Air density is a known parameter and wind speed is a forecasted variable, whereas the drag coefficient is calculated using an empirical correlation. The correlation's accuracy has brewed a controversy of its own for more than half a century. This review paper examines the lineage of drag coefficient correlations and their acceptance among scientists.

Regional sea level changes were studied in the NorthWest Indian Ocean (NWIO). Basically, the processes affecting regional sea level changes can be divided into dynamic and quasi-static components. In the present study, dynamic sea level changes were evaluated by applying statistical methods such as Trend, Empirical Orthogonal Function (EOF), Spectral and Correlation analyses to the mean sea level anomaly, surface heat flux, and wind stress data. In addition, quasi-static sea level changes were examined by considering the inverted barometer effect. The results indicated that the maximum sea level rise is mostly observed in areas adjacent to the Gulf of Aden, and the minimum sea level rise is seen at the centre of the region, near the equator and oriented towards the SW. In general, in NWIO, the main factors affecting sea level changes are weakened and intensified with a one-year period. The correlation coefficients of heat flux and wind stress with the 2nd EOF of the sea level are larger than those of other modes so that the effect of internal factors, such as seasonal change, is, generally, smaller than the effect of external factors such as El-Nino-Southern Oscillation. The direction of prevailing winds in the region causes the positive sea level anomalies by Ekman suction and increasing the depth of the tropical thermocline. The inverted barometer effect on the sea level changes is significant in most of the months, except December, in such a way that it decreases in the cold months by moving towards high latitudes, while increases in warm months by moving to high latitudes. The distribution of non-barometric effects in the Arabian Sea indicates that they are caused by interactions with the Indian Ocean mostly from the southern areas of the Arabian Sea and the intensity of these effects decreases northwards and westwards during the year.

Interannual and climatological variations of wind stress drag coefficient (CD) are examined over the global ocean from 1998 to 2004. Here CD is calculated using high temporal resolution (3- and 6-hourly) surface atmospheric variables from two datasets: 1) the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and 2) the Navy Operational Global Atmospheric Prediction System (NOGAPS). The stability-dependent CD algorithm applied to both datasets gives almost identical values over most of the global ocean, confirming the validity of results. Overall, major findings of this paper are as follows: 1) the CD value can change significantly (e.g., >50%) on 12-hourly time scales around the Kuroshio and Gulf Stream current systems; 2) there is strong seasonal variability in CD, but there is not much interannual change in the spatial variability for a given month; 3) a global mean CD ≈ 1.25 × 10−3 is found in all months, while CD ≥ 1.5 × 10−3 is prevalent o...

Available climatic and atmospheric analysis data have been used to prepare forcing functions for the Black Sea numerical model, based on the Bryan-Semtner-Cox Modular Ocean Model and including parameterizations for the atmosphere-ocean exchange, inflow through the strait of Bosphorus and the Mediterranean plume. Atmospheric data from different sources are compared and the drawbacks of some of them illustrated. A new wind stress data set, based on ship observations, is prepared. Compared to the existing wind stress estimates, the present ones use additional data and more accurate parameterization of the boundary layer physics. The intercomparison between forcing data sets is focused on the heat flux and freshwater flux at the sea surface.The model simulates adequately vertical stratification, seasonal variability and horizontal patterns. Five data sets for heat flux, freshwater flux and wind stress are used in different combinations to study the model response. The large differences ...

The relationships between shelterbelt (tree windbreak)-induced microclimate and muskmelon (Cucumis melo L.) growth and development were investigated at the Univ. of Nebraska-Lincoln Agricultural Research and Development Center near Mead, Nebr., during the 1992 and 1993 growing seasons. Wind speed, wind direction, air and soil temperatures, relative humidity, and soil moisture were monitored in both sheltered and nonsheltered areas. Plant growth parameters (plant height, vine length, plant dry weight, and leaf area) were measured at various stages of development. Shelterbelts provided improved growing conditions for muskmelon transplants. Direct wind damage and duration of higher wind speeds were reduced 47% to 56% in sheltered areas. Air temperatures in sheltered areas were slightly higher during daytime and slightly lower at night, and significantly so early in the growing season. Relative humidity was increased significantly in sheltered areas in 1992 and, while higher in 1993, th...

The Third Acoustic Surface Reverberation Experiment (ASREX III) took place from December 1993 to March 1994 at Site L (34 deg N, 70 deg W) in the mid-Atlantic. As part of this experiment, two moorings were deployed to measure the environmental background. A meteorological and oceanographic mooring was deployed to characterize the surface wind stress, buoyancy flux, and the current and temperature structure over the top 500 meters. A Seatex Wavescan buoy was deployed to characterize the directional wave spectrum. This report presents results from these moorings. Wind speeds up to 25 m/s were seen, with significant heat losses (up to 1050 W/ sq. m) when cold continental air moved out over the warm Atlantic. The wave heights ranged up to 8 m, with significant wave heights of several meters persisting for relatively long periods. Wave height and period, nondirectional spectra, directional spectra and a typology of wave events are presented and related to surface forcing.

A technique referred to as Normal Mode Analysis (NMA) has recently been developed for representing total vector CODAR HF radar data in Monterey Bay. These modes satisfy the coastal boundary constraint of no flow normal to the shore, and inherently represent both divergent and rotational flow as two sets of ortho-normal basis functions. In prior investigations by others, the domain

Different measures of wind influence the ocean in different ways. In particular, the time-averaged mixed layer turbulent energy production rate is proportional to 〈u3*〉, where u* is the “oceanic friction velocity” that is based on wind stress. Estimating 〈u3*〉 from monthly averages of wind stress or wind speed may introduce large biases due to the day-to-day variability of the direction and magnitude of the wind. The authors create monthly climatologies of 〈u3*〉 from daily wind stress measurements obtained from the Goddard Satellite-based Surface Turbulent Fluxes version 2 (GSSTF2; based on satellite microwave measurements), the Quick Scatterometer (QuikSCAT; based on satellite scatterometry measurements), and the National Centers for Environmental Prediction (NCEP) reanalysis wind. The differences among zonal averages of these climatologies and of a similar climatology based on the da Silva version of the Comprehensive Ocean–Atmosphere Data Set (COADS) have a complex dependence on ...

Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus—a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driv...

High-resolution mesoscale model sea surface temperature (SST) analyses and surface wind stress forecasts off the U.S. West Coast are analyzed on monthly time scales for robust signatures of air–sea interaction as the surface winds encounter ocean surface features such as SST fronts, filaments, and eddies. This interaction is manifest by the linear relationship, or coupling coefficient, between the downwind SST gradient and wind stress divergence and between the crosswind SST gradient and wind stress curl evident from analysis of fields averaged over 29 days. This study examines fields from the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model, spanning the summer months, June–September, for four consecutive years, 2002–05. Relative to several models evaluated previously, coupling coefficients are much closer to those calculated from Quick Scatterometer (QuikSCAT) satellite measurements. In addition, the summertime correlation between the wind stress derivative fiel...

The modulation of radar backscatter by long ocean waves can, to first order, be described by a linear modulation transfer function (MTF). The complex MTF can be separated into a part describing purely geometrical effects and the “hydrodynamic MTF” resulting from the modulation of short surface waves by longer waves. According to previous theories, the hydrodynamic MTF should be independent of radar polarization. Experimental results show that this is not valid. Furthermore, the measured hydrodynamic MTFs for high radar frequencies are often larger than expected. The authors show that these effects can be basically explained by a three-scale composite surface model, which takes into account the second-order modulation of the radar backscatter by intermediate-scale surface waves. Furthermore, the proposed model includes a modulation of the wind stress over the long surface waves

From almost 7000 near-surface eddy-covariance flux measurements over the sea, the authors deduce a new air–sea drag relation for aerodynamically rough flow:[Formula: see text]Here u* is the measured friction velocity, and UN10 is the neutral-stability wind speed at a reference height of 10 m. This relation is fitted to UN10 values between 9 and 24 m s−1. A drag relation formulated as u* versus UN10 has several advantages over one formulated in terms of [Formula: see text]. First, the multiplicative coefficient on UN10 has smaller experimental uncertainty than do determinations of CDN10. Second, scatterplots of u* versus UN10 are not ill posed when UN10 is small, as plots of CDN10 are; u*–UN10 plots presented here suggest aerodynamically smooth scaling for small UN10. Third, this relation depends only weakly on Monin–Obukhov similarity theory and, consequently, reduces the confounding effects of artificial correlation. Finally, with its negative intercept, the linear relation produce...