Showing papers on "Wind stress published in 1975"

Variation of the sea surface drag coefficient with wind speed

Abstract: Eddy correlation measurements of wind turbulence obtained at a sand spit on Sable Island, Nova Scotia, in winds ranging from gentle breeze to strong gale force agree with other recent measurements over water. There is a significant increase in the drag coefficient with wind speed which is well described by the equation of Charnock (1955). The heat transfer coefficient is slightly lower than the drag coefficient.

Topographically generated internal waves in the open ocean

Abstract: The generation of internal waves by the interaction of deep ocean flows with bottom topography is considered. The interaction of quasi-steady currents with the bottom topography is found to produce an internal wave drag and associated momentum flux of roughly ½ dyn/cm2, which is comparable to the average wind stress on the ocean surface. The waves are probably dissipated by critical layer phenomena in the lowest kilometer or so of the ocean, the result being a wave-induced vertical mixing coefficient of order 10 cm2/s in that portion of the water column. The interaction of the barotropic tide with the bottom topography is found to result in a flux of energy of order 1 erg/cm2 s into the internal tide, which may represent a nonnegligible sink of the tidal energy. This mechanism appears to be capable of supplying a significant portion of the observed internal wave energy in the ocean. The internal tide is probably dissipated by inherently nonlinear phenomena: spectral transport by weak interactions and, in the upper oceans, strong interactions manifested by localized instabilities resulting in isolated patches of turbulence.

Wind-induced drift currents

Abstract: Systematic measurements of drift currents below and of airflows above an air-water interface have been made under various wind conditions. The current near but not immediately below the water surface is found to follow a Karman-Prandtl (logarithmic) velocity distribution. The current immediately below the water surface varies linearly with depth. The transitions of the current boundary layer to various regimes appear to lag behind, or to occur a t a higher wind velocity than, those of the airflow. The fraction of the wind stress supported by the wave drag seems to vary with the wind and wave conditions: a large fraction is obtained at low wind velocities with shorter waves and a small fraction is obtained a t high wind velocities with longer waves. At the air-water interface, the wind-induced current is found to be proportional to the friction velocity of the wind. The Stokes mass transport, related to wave characteristics, is only a small component of the surface drift in laboratory tanks. However, in terms of the fraction of the wind velocity, the mass transport increases, while the wind drift decreases, as the fetch increases. The ratio between the total surface drift and the wind velocity decreases gradually as the fetch increases and approaches a constant value of about 3·5% at very long fetches.

The influence of the “tidal stress” on the residual circulation

Abstract: The residual current field in the sea is defined as the mean velocity field over a time sufficiently long to cancel transitory wind currents and tidal oscillations. The hydrodynamic equations governing the residual circulation are established and it is shown that, in the regions of intensive tides, the tidal motion has a cogent influence on the residual flow pattern. This effect which arises from the non linear terms is equivalent to the application of a “tidal stress” which combines with the wind stress to drive the water motion. The tidal stress is calculated in the Southern Bight of the North Sea from the results of a numerical tidal model and the residual circulation is computed. The comparison with the circulation obtained when neglecting the tidal stress shows determinant differences enforcing the theory. DOI: 10.1111/j.2153-3490.1975.tb01701.x

Wind-generated gravity-capillary waves: laboratory measurements of temporal growth rates using microwave backscatter

Abstract: The growth rates of wind-induced water waves at fixed fetch were measured in a laboratory wave tank using microwave backscatter. The technique strongly filters out all wavenumber component pairs except for a narrow window at the resonant Bragg scattering conditions. For these waves the spectral amplitude was measured as a function of the time after a fixed wind was abruptly started. The radars were aligned to respond to waves travelling in the downwind direction at wavelengths of 0·7-7 cm. Wind speeds ranged from 0·5 to 15 m/s. Fetches of 1·0, 3·0 and 8·4 m were used. In every case, the spectral amplitude initially grew at a single exponential rate β over several orders of magnitude, and then abruptly ceased growing. No dependence of the growth rate on fetch was observed. For all wavelengths and wind speeds the data can be fitted by \[ \beta (k,u_{*},{\rm fetch})=f(k)\,u^n_{*}, \] with n = 1·484 ± 0·027. Here u* is the friction velocity obtained from vertical profiles of mean horizontal velocity. For each wind speed, f(k) had a relative maximum near k = kn ≃ 3·6 cm−1. Rough estimates of β/2ω, where ω is the water wave frequency, and of the wind stress supported by short waves indicate that the observed growth rates are qualitatively very large. These waves are tightly coupled to the wind, and play a significant role in the transfer of momentum from wind to water.

Radio measurements of oceanic winds at long ranges: An evaluation

Abstract: Oceanic winds were measured locally by anemometers and remotely by an HF skywave radar at ranges exceeding 3000 km. Wind velocity was deduced from sea backscatter Doppler spectra. These spectra were often perturbed by ionospheric motion, yet wind direction was measured to within ±16° and wind speed to within ±4 m sec−1. Better measures of wind speed should exist at shorter ranges or with better ionospheric conditions.

Aerodynamic boundary-layer adjustment over a crop in neutral stability

Abstract: An experimental study of the modification of the neutral wind profile as air flows to a rougher surface is presented. The analysis is based on wind profiles measured at four locations extending about 100 m downwind from the leading edge of a mature wheat crop. The form of the modified wind profile, and the rate of internal boundary-layer growth are analyzed in terms of a non-dimensional wind velocity. Friction velocities, based on wind-profile computations, are also examined at different points in the flow field. Boundary-layer growth was more rapid than expected, but could be approximated by a 4/5th power of the fetch if a roughness factor is included. It is suggested that simple height:fetch ratios, such as 1:100 be avoided, especially where large roughness-length changes are involved.

Wind-tunnel simulation of the atmospheric boundary layer: a report on Euromech 50

Abstract: The 50th Euromech Colloquium, on wind-tunnel simulation of the atmospheric boundary layer, was held in Berlin from 23–25 September 1974. Thirty-eight participants from eleven countries were present. Papers were presented describing and analysing different methods of simulation of neutral, stable and unstable atmospheric conditions in various types of wind tunnel. Numerous applications of wind-tunnel simulations were described or mentioned in the papers and the discussion sessions. Some conclusions about the validity, the techniques, the limitations and future developments of wind-tunnel simulations were reached in discussion. Tables are presented in appendix A listing the institutes in Europe and the U.S.A. of actual or invited participants where wind tunnels are used for simulation work; also listed are the characteristics of the wind tunnels and relevant measurements of the simulated atmospheric boundary layers, to enable comparisons to be made between different techniques.

MODE Bottom Experiment

Abstract: Pressure fluctuations on the deep seafloor at frequencies below inertial and tidal have been measured. Between 0.1 and 1 cycle per day the variance is about 2 mb2, spectra diminish with increasing frequency as ω−n, n=1.5 to 2, and a signal-to-instrument noise ratio of 10 dB is achieved. Fluctuations are in phase and highly coherent within the MODE area (>0.95 at 200 km) and even with inferred (atmosphere plus sea level) Bermuda subsurface pressures (0.8 at 700 km). Station differences (to which MODE-sized eddies would make the principal contribution) are relatively small. The large horizontal scale of the recorded bottom pressure fluctuations resembles that of atmospheric pressure, yet the coherence locally between atmospheric and bottom pressure is slight; the recorded fluctuations may be related to a barotropic ocean response to a variable wind stress on the subtropical gyre. Bottom temperature records show “sudden” (1 day) changes of order 30 millidegrees Celcius separated by long intervals (2...

Some Features of Wind Action on Shallow Lakes

Abstract: The shear stress due to wind action on a shallow lake or lagoon creates a velocity distribution in the vertical direction. Assuming the vertical turbulent diffusion coefficient, K, is constant, the...

A Theory of Steady Wind-Driven Currents in Shallow Water with Variable Eddy Viscosity

Abstract: A theory is given for steady wind-driven currents in shallow water (friction depth comparable to total depth) in which the vertical eddy viscosity varies linearly with depth, from zero at the bottom to a maximum at the surface. The theory is presented in a form suitable for numerical computations of currents in real, enclosed basins. The local surface value of the vertical eddy viscosity depends on the surface wind stress, the bottom roughness, and the flow itself; this leads to a quasi-linear equation for the determination of the surface slope or the vertically-integrated mass flux. Results are given for the simple case of a pure drift current in water of uniform depth, and these results are compared with those for a constant vertical eddy viscosity.

The Relationship Between Fluctuations in Sea Level, Wind Stress and Sea Surface Temperature in the Equatorial Pacific

Abstract: Correlations among sea level, wind stress and sea surface temperature at various lags have been used to determine the relationship between these parameters in the Pacific equatorial region 10°N to 10°S. Seasonal sea level in the coastal upwelling region depends on the magnitude of the meridional component of the southeast trade. Seasonal sea level along and south of the equator (to about 110°W) depends mainly on the temperature of water advected from the coastal upwelling region. Seasonal sea level in mid-ocean is mainly a function of the degree of set-up by the zonal component of the local wind stress. In the Countercurrent trough, seasonal sea level varies inversely with the magnitude of the local meridional shear except in spring when it is directly proportional to set-up by the zonal component of the northeast trade. Year-to-year sea level fluctuations from about 4°N to 10°S in the eastern half of the ocean are caused primarily by fluctuations in the temperature of water advected away from th...

Relation between Mean Sea Level, Current and Wind Stress on the East Coast of Australia

Abstract: Five-day mean sea level differences between Evans Head (29o 07'S.) and Coffs Harbour 30o 19'S.), and between Coffs Harbour and Crowdy Head (31o 50'S.) were regressed on estimates of longshore current acceleration, mean longshore current and longshore wind stress, with the following results: (i) A relation was found between sea level difference from Coffs Harbour to Crowdy Head, and current acceleration. There was no similar relation for the section Evans Head to Coffs Harbour, and no reason could be found for the difference in behaviour between the two sections. (ii) A weakly defined relation was found, in both sections of the coast, between sea level difference and the square of the mean longshore current (a friction effect). (iii) An apparent relation was found, again in both sections of the coast, between sea level difference and longshore wind stress. This relation was more marked than expected from theory. The longshore currents were obtained from ships' drift, and covered a period of 2 years. The current data show a southward drift of current pattern, at an average rate of 9 km day-1. They also show a clear correlation between currents at the shelf edge (approximately 19 km offshore) and currents nearer shore (approximately 6.5 km offshore). It was found that the nearer-shore currents lagged the shelf-edge currents by between 7 and 10 days. Time and space correlations of the shelf-edge currents confirm earlier estimates from similar data. A frequency spectrum of the shelf-edge currents showed a broad maximum in the period range 50-170 days.

The influence of the "tidal stress" on the residual circulation Application to the Southern Bight of the North Sea

Abstract: The residual current field in the sea is defined as the mean velocity field over a time sufficiently long to cancel transitory wind currents and tidal oscillations. The hydrodynamic equations governing the residual circulation are established and it is shown that, in the regions of intensive tides, the tidal motion has a cogent influence on the residual flow pattern. This effect which arises from the non linear terms is equivalent to the application of a “tidal stress” which combines with the wind stress to drive the water motion. The tidal stress is calculated in the Southern Bight of the North Sea from the results of a numerical tidal model and the residual circulation is computed. The comparison with the circulation obtained when neglecting the tidal stress shows determinant differences enforcing the theory.

The Trade Wind Field Over the Pacific Ocean. Part I. The Mean Field and the Mean Annual Variation

Abstract: : The trade wind field over the Pacific Ocean between 30N and 30S has been studied on the basis of five million wind observations made by ships. Data were averaged for areas of 2 degrees latitude and 10 degrees longitude to resolve northsouth gradients in the wind field adequately. Mean monthly maps of the wind vector and of the wind stress vector were produced and the development of the trade wind field throughout the year is discussed. Either trade wind system is largest and strongest during the winter of the respective hemisphere. It is shown that the area covered by the northeast trades is smaller than the area covered by the southeast trades, but the northeast trades have a stronger mean wind stress and a larger seasonal variation both in area and mean stress. Bimonthly mean maps of the divergence of the wind and of the wind stress curl are also produced. The wind divergence shows clear relations to cloud cover; the maps of wind stress curl show considerable detail and more structure and seasonal variation than expected.

An investigation of suspended material concentrations in eastern Long Island Sound

Abstract: A 2-year record of monthly observations of suspended material concentrations at a network of 11 stations in eastern Long Island Sound is used to detail the characteristics of the concentration field and the factors governing its variability. These suspended material distributions display a high degree of spatial and temporal variability, there being only weak correlation between concentrations and concurrent salinity. This behavior contrasts sharply with observations in other regions of the sound. To determine the relative importance of hydrodynamic, meteorological, and biological factors, an ensemble average of selected station data is introduced. This average displays a seasonal variability that can be represented by the combined effects of streamflow and wind stress. Streamflow serves to produce a persistent background concentration. The occurrence of higher frequency fluctuations due to aperiodic discharge events appears limited by the volume and mixing characteristics of the eastern sound. Wind events will dominate the concentration field if high stress levels are maintained for more than 48 hours. Duration requirements are most commonly satisfied during the winter months. Materials introduced by streamflows and wind stress are distributed by the high energy tidal stream. Biological factors exert minor influence on the variability of the concentration field. A review of this system suggests that the eastern sound is more properly viewed as a coastal embayment than as an estuary. Mixing in this area establishes the eastern boundary conditions for the remainder of the sound.

Results of sea surface mapping in the Peru upwelling system1

Abstract: Sea surface maps of temperature, salinity, nitrate, silicate, phosphate, and fluorescence were produced almost daily during a 6-week cruise (PISCO) in the Peru upwelling system in the austral fall, 1969. The maps were produced by a shipboard computer from data gathered with the ship underway. The maps show persistent “plumes” of freshly upwelled water associated with coastal irregularities and prominent bathymetric features. The information on the location, orientation, and extent of these plumes was used to locate stations where primary productivity experiments were carried out. The definition of persistent plumes has led to the development of successful two-dimensional simulation models of the ecosystem. One of the primary difficulties in studies of time-varying mesoscale phenomena in the ocean, such as coastal upwelling, is that large surface gradients and the rapid response of the upper ocean to changes in wind stress make it impossible to synthesize a synoptic picture from discrete stations taken over many days or weeks. More truly synoptic sampling is required. Remote sensing has shown considerable promise for such mapping of temperature and chlorophyll, but the use of a shipboard system has the advantage that many more variables can be determined (Kellcy 1975). We developed such a shipboard system for the study of marine ecosystems and used it during a cruise of the RV Thomas G. Thompson to the upwelling area off the coast of Peru near 15’S in 1969. During ’ Contribution No. 841 from the Department of Oceanography, University of Washington. This research was supported by the International Biological Program (NSF GB-35880X-Upwelling Biome) and the Office of Naval Research (N-0001467-A-0103-0014). The preparation of this paper was supported in part by National Science Foundation GX 33502 [Coastal Upwelling Ecosystems Analysis ( NSF-IDOE ) I. ’ Current address: School of Natural Sciences, San Francisco State University, San Francisco, California 94132. ” Current address: Division of Oceanographic Sciences, Brookhaven National Laboratories, Upton, New York 11973. 4 Curent address: Bigelow Laboratory of Marine Science, West Boothbay Harbor, Mainc 04575. this cruise (PISCO), 20 March-3 May 1969, data were acquired and digitized by a shipboard data system and analyzed by shipboard computer to produce sea surface maps of the concentrations of variables important to the understanding of the ecosystem. Maps of the sea surface, temperaturc, salinity, nitrate, nitrite, silicate, phosphate, and fluorescence were produced on a grid 70 nautical miles ( 130 km) long in the longshore dimension and 15 nautical miles (28 km) wide in the offshore dimension ( Fig. 1). Since much of the station work on the cruise was confined to the daylight hours because sunlight was necessary for the experiments conducted, the night was used for underway mapping of the relevant sea surface properties. Typically about a third of the total grid was covered on a given night. Maps were concentrated in the central portion of the grid, and occasionally the entire grid was covered by continuous steaming for 36 h. With the aid of the shipboard computer, maps from a night’s run could bc plotted in the early morning and used to plan the location of the day’s stations. Thus, the sampling program could bc adapted to conditions measured only a few hours before. We wish to thank L. and R. Olund for their assistance during the cruise and J. Glass and M. Friebertshauser for their assistance in analysis of data. LIMNOLOGY AND OCEANOGRAPHY 784 SEPTEMBER 1975, V. 20( 5) Surface maps of Peru upwelling 785 UNDERWAY SAMPLING DATA FLOW

Physical model study of circulation patterns in Lake Ontario1

Abstract: A distorted hydraulic model of Lake Ontario has been constructed and operated in a rotating laboratory. The model study includes the cffccts of the earth’s rotation, gravity, and hydraulic through-flow. Boundary shear in the model was checked against theoretical predictions of scichc decay. Wind shear was adjusted to achieve appropriately scaled drift velocities in the model. Observed surface and subsurface circulation patterns are presented for a homogeneous and stratified lake model with and without a westerly wind. Bordcrcd on the north by Canada, and on the south by New York State, Lake Ontario is the easternmost of the Great Lakes. Water from the other Great Lakes drains into it through the Niagara River and lcavcs by way of the St. Lawrcncc- River. The lake has the following physical characteristics : length, 306 km; average width, 85.3 km; average depth, 86.3 m; maximum depth, 256 m; volume, 1,681 kms; and surface area, 19,477 km2. The Niagara River inflow averages just over 5,560 m3 s-l while the outflow through the St, Lawrence River averages about 6,640 m3 s-l; the difference is accounted for by the net accumulation of rainfall and the tributary inflows from the Lake Ontario drainage basin which covers about 70,707 km2. The purpose of this physical model study was to acquire a basic understanding of the behavior of the Lake Ontario water mass in response to a wind stress at the free surface with and without thermal stratification. Thr: major inflow and outflow streams were modeled. The model was rotatcd to simulate the effect of the earth’s rotation on the motion of large water bodies. This physical modcling approach is similar to earlier investigations of Lake Eric (Rumer and Robson 1968; Bucchi

The Trade Wind Field Over the Pacific Ocean. Part II. Bimonthly Fields of Wind Stress: 1950 to 1972,

Abstract: : The trade wind field over the Pacific Ocean between 30N and 30S has been studied on the basis of five million wind observations taken from ships. Data were averaged for areas of 2 degrees latitude and 10 degrees longitude to resolve adequately the north-south gradients in the wind field. Bimonthly mean maps of the wind stress vector were produced for the period from 1950 to 1972. Indices of the size and overall strength of the northeast and the southeast trades are defined, and time series of these indices are presented for the period from 1948 to 1972. Interannual variations and the most outstanding seasonal anomalies in the trade wind field are discussed briefly.

On the Possibilities of Coastal, Mid-Shelf, and Shelf Break Upwelling

Abstract: The steady-state circulation on a continental shelf under the combined influence of a wind stress, a surfacedensity distribution, and a longshore current over the shelf break is investigated in a linear, β-plane modelthat allows a longshore pressure gradient. The problem is quasi-two-dimensional and lends itself readily toa standard boundary-layer analysis. For the range of parameters considered, the hydrostatic Lineykin layerallows a vertical mass transport into the surface Ekman layer to compensate for the one-sided divergencecreated by the wind stress at the coast and is, therefore, primarily responsible for coastal upwelling. Anequatorward longshore current over the shelf break, on the other hand, contributes to a shelf break upwelling due to the Sverdrup relation. There is, in this case, also a possibility for a poleward undercurrentover the continental shelf. When the equatorward longshore velocity at the shelf break bottom is sufficientlylarge, however, the poleward undercurrent may not ex...

The Influence of Longitudinal Variations in Wind Stress Curl on the Steady Ocean Circulation

Abstract: The influence of longitudinal variations in wind stress curt on the steady circulation in a rectangular ocean basin is investigated analytically in a linear barotropic model It is shown that longitudinal variations in the interior circulation are produced by longitudinal variations in the magnitude of a wind stress curl of constant (negative) sign If friction is small in the interior, the east-west variation in southward flow is directly proportional to that of the applied wind stress curl in accordance with the Sverdrup vorticity balance Examples show that when the wind stress curl has a maximum in the center of the basin, the southward flow is also concentrated in the center of the basin When the wind stress curl has a minimum in the center of the basin, the southward flow is concentrated in two regions, one on either side of the minimum curl This variation in southward flow causes a concentration in cast-west flow along the northern and southern boundaries of the basin, which is not obvio

Formation of Meanders, Fronts, and Cutoff Thermal Pools in a Baroclinic Ocean Current

Abstract: Using an analytical model similar to that previously applied by the authors to the atmosphere, calculations are made showing how second-order, nongeostrophic effects can modify a two-layer baroclinic wave system that grows exponentially from a small perturbation in a uniform zonal ocean current. It is shown that many of the asymmetric features characteristic of meandering ocean currents develop, including “fronts” and cutoff cyclonic cold pools to the south and anticyclonic warm pools to the north of the axis of the mean current. The implication is that all of these features can be viewed as being the simultaneous consequence of baroclinic instability (with attendant second-order finite-amplitude effects) of a broader, more uniform current that might tend to be forced externally by the wind stress and thermohaline processes.

Tide and fair-weather wind effects in a bar-built louisiana estuary

Abstract: An in-depth, fair-weather, field study in July 1972 provided information about the response of the water level of Caminada Bay, an extremely shallow, bar-built Louisiana estuary The water surface elevation was recorded at three locations in the bay along the other parameters, an equipotential surface was established, and the time-dependent variations of a slope vector along the surface gradient were computed It was found that the instantaneous fair-weather wind stress induced a slowly oscillating set-up around a time-averaged slope magnitude of 15×10-6 rad This constituted less than 50% of the measured time-averaged slope The remaining time-averaged slope is accounted for by tidal nonlinearities The instantaneous slope vector was found to rotate or oscillate in the horizontal plane with a diurnal period Tidal input through two entrances governed this behavior, while the wind stress and atmospheric pressure gradients served only to modify the direction of the surface slope In general, on the diurnal scale, tidal rather than wind effects dominate the dynamics of Caminada Bay However, the mean water level responded to the wind direction on a time-scale longer than one day Winds parallel rather than normal to the coast controlled the water elevation, indicating an Ekman effect

Properties of pressure fluctuations in an atmospheric boundary layer

Abstract: From experimental data it is shown that there is a relationship between measured wind speed and associated micropressure levels. It is also shown that turbulent eddies associated with the wind vanish within distances of five to six times their size, and that these eddies exhibit normal dispersion. These results confirm, at the atmospheric scales, results previously observed only in model experiments.

On the relation between surface wind and pressure gradient, especially in lower latitudes

Abstract: Observations show that the angle between surface wind and isobar increases equatorward in low latitudes while the ratio of surface to geostrophic wind speed decreases. With the use of Southern Hemisphere winter fields of surface pressure and temperature over the oceans, and Rossby number similarity theory (including the effects of baroclinicity) in several different forms, the expected latitudinal variation of the angle and ratio has been computed. A check has also been made of mean ATEX and BOMEX data. It appear that the variations with latitude are probably mainly due to baroclinicity. With this factor taken into account, similarity theory fairly adequately explains the observations.

A report on the continental shelf circulation and coastal upwelling

Abstract: The bathymetry and hydrography of the coastal regime of continents are a complex maze which belies their physical description in simple shapes and coherent water masses. Each river outflow, shelf canyon, bay, harbor, and sandbar has its distinct character and depending on a variety of atmospheric conditions, is bordered by a distinct water mass. The shallow beach zone has been a region of intense study which has been led by coastal engineers for several decades. In reviewing the advances in research in coastal oceanography it is heartening to find that a significant body of unifying ideas and models for the deeper continental shelf emerges. This indeed must be inevitable because the dynamic structure of the oceanic water mass is constrained by Newton's laws of high Reynolds number and the second law of thermodynamics of high Peclet number in which the variety of local conditions become hydrodynamically similar. However, such an overview has been a long time coming in the United States because only in the past 10 years have direct observations of continental shelf water motions been made in a manner by which the variability of the hydrodynamic regime on the shelf can be clearly documented. The most significant advance is that coastal oceanographers have begun measuring, describing, and modeling the long-wave shallow water turbulence on the continental shelf. Past interpretation of sea surface and sea bed drifter statistics and the classical hydrographic file implies that the synoptic continental shelf circulation patterns are a morass; however, a more focused picture emerges from long time series of direct current measurements, closely spaced and frequently sampled hydrographic surveys, and infrared and color satellite imagery. It is found that continental shelf circulation principally varies with the (1) local variations in the atmospheric wind stress and thermohaline forcing on both synoptic and seasonal time scales, (2) eddies and long waves which impinge from the deep sea, and (3) tidal phenomena.

Effective wind stress over the great lakes derived from long‐term numerical model simulations

Abstract: Numerical models were used to compute water circulations throughout the 1970 shipping season for Lake Erie and for the 1972 International Field Year on Lake Ontario. Simultaneous computations of surface elevations were compared with observed water levels to adjust the model results after the fact. As a by‐product of these simultations, effective stress coefficients over water can be estimated. The results support earlier evidence that the effective wind stress over water is larger than indicated by atmospheric boundary layer measurements.