bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal transformation of shallow water wave energy
Authors: Aranuvachapun Sasithorn , Thornton Edward B.
Published: February 2008

The surface wave spectra from the Atlantic Ocean Remote Sensing Land‐Ocean Experiment (ARSLOE), during the passage of a 26‐hour storm, were subjected to an empirical eigenfunction analysis. Results from the analysis are interpreted as the spatial and temporal variation of surface gravity waves propagating from deeper water into the shallow region where breaking finally occurs. The temporal variation is found to be approximately 7–17% of the total variance in the data and is considered as stochastic, with a fluctuation of about 2–3 cycles that appear correlated with the variation of the atmospheric forcing. The spatial variation (1–3%) is significantly less than the temporal variation but exhibits a deterministic part, indicating that the wave processes associated with the spatial variation can be considered deterministic. The principal eigenfunctions obtained from the analysis provide a good representation of the principal variations in the wave spectra as shown by the first eigenvalue of the covariance matrices. The radiative transfer equation is projected onto the eigenvector space, and the source function obtained from the suitable projection function is presented. By using the information extracted from the empirical eigenfunction analysis, various source functions for the wave field are inferred. The source functions evaluated in the present study are associated with the wave mechanisms of refraction and shoaling, atmospheric input, bottom friction, and wave‐wave nonlinear interaction. The functions provide a good picture of the spectral wave energy balance, although further development of the current work can provide more detailed information about the energy transfer and may enhance the present picture of wave energy balance in the shallow water.
Topographic generation of an eddy at the edge of the East Greenland Current
Authors: Smith David C. , Morison J. H. , Johannessen J. A. , Untersteiner N.
Published: February 2008

Wadhams and Squire [1983] describe an ice‐water eddy at the edge of the East Greenland Current, located at about 79° and 1°E. The eddy has been sighted earlier [Vinje, 1977] and appears to occur in that general location with some regularity. Wadhams and Squire explain the eddy in terms of baroclinic instability. The criteria of Griffiths and Linden [1982] and Phillips [1954] suggest that the East Greenland Current is baroclinically unstable, and Phillips' theory indicates that the most unstable wavelength of a sinusoidal velocity perturbation is 50 km, in agreement with the approximate size of the observed eddy.
Estimates of the geostrophic stream function in the western North Pacific from XBT surveys
Authors: Koblinsky C. J. , Bernstein R. L. , Schmitz W. J. , Niiler P. P.
Published: February 2008

The upper ocean temperature and dynamic height fields are correlated in the western North Pacific Ocean. This relationship can be used to map a relative geostrophic stream function of the Kuroshio Extension using temperature data from expendable bathythermograph (XBT) surveys. We have examined the ability of the North Pacific ship of opportunity XBT program, known as TRANSPAC, to carry out this procedure. Estimates of 600/1200 dbar geostrophic shear were generated from the XBT data utilizing objective mapping techniques. These estimates were compared with measured currents at 600 m relative to 1200 m along 152°E from 27°N to 42°N. The estimated and measured relative currents are positively correlated, with an rms error of ±6 cm/s over a measured dynamic range of 30 cm/s. However, the XBT estimated shears consistently underestimate the measured values by a factor of 2 to 3. The underestimate of the amplitude is the result of both undersampling and mapping produres that eliminate high wavenumber contributions of the dynamic height variability. These factors appear to be responsible for previous differences in amplitude between directly measured and TRANSPAC XBT estimated values of relative eddy kinetic energy and Reynolds stress. The TRANSPAC XBT survey can only monitor qualitatively the dynamic topography of the Kuroshio Extension meanders and rings. The variability outside of the extension with a temperature range of 3°C cannot be resolved because of inaccuracies in the temperature‐dynamic height relationship. To monitor the Kuroshio Extension variability in the future, it is recommended that TRANSPAC XBT resources in the western North Pacific concentrate on obtaining a denser sample of the field during the fall and winter seasons because of incomplete ship track coverage in spring and summer.
A model of sea‐ice front instabilities
Authors: Killworth Peter D. , Paldor Nathan
Published: February 2008

The linear instability of an infinite ice front overlying a passive ocean is demonstrated for the case where the ice concentration satisfies a simple condition far from the front. The long wave analytical estimates are confirmed numerically for an ice dispersivity that is not too small, but a very large dispersivity stabilizes the front. Inclusion of cross‐frontal wind stress merely alters the mean state but does not affect the instability process.
Ice‐induced vertical circulation in an Arctic fiord
Authors: Horne Edward P. W.
Published: February 2008

CTD and nutrient data taken in South Cape Fiord next to a glacier face show strong evidence of upwelling. In addition a region of down welling is found from 0.5 km to 5 km from the ice. Intruding layers with thicknesses consistent with lab measurements are found near the ice. A phytoplankton bloom is found to be going on in the fiord, and an upwelling velocity of 2.5×10−4 m s−1 is calculated by assuming that all the nitrogen required by these cells is up welled from the deep water within 10−2 m of the glacier. Mechanisms to drive the downwelling are discussed.
Microwave probing of shallow water bottom topography in the Nantucket Shoals
Authors: Valenzuela G. R. , Plant W. J. , Schuler D. L. , Chen D. T. , Keller W. C.
Published: February 2008

Coordinated microwave and in situ measurements were performed during the 1982 Naval Research Laboratory Phelps Bank experiment (Nantucket Shoals). The measurements including airborne X band APD‐10 synthetic aperture radar imagery and airborne X and shipboard L band coherent radars together with extensive hydrographic, oceanographic, and meteorological information are reported. The microwave measurements show large variations of backscatter power (over 20 dB at both L and X band) for winds less than 7 m/s. Generally, regions of strong backscatter cluster near large bottom slopes, suggesting their generation by the bottom topography. However, for winds greater than 7 m/s (7–12 m/s in this experiment) the variations of microwave backscatter power decrease to 2–3 dB for both frequency bands and become decorrelated from the bottom topography. An explanation for this may be that wind drift near the surface layer tends to mask the ocean surface features relating to the bottom topography when its magnitude is comparable to the rotary tide and the residual circulation due to tidal stress. A current gradient (front) seemingly not related to bottom topography also produced 20‐dB variations in the power backscattered to the L band radar.
Deep‐sea circulation in the Alboran Sea
Authors: Pistek P. , de Strobel F. , Montanari C.
Published: February 2008

Alboran Sea circulation between 220 and 1100 m depth is studied. Interaction between three types of water masses in this area causes a complicated flow pattern. Atlantic water flowing as a jet through the Strait of Gibraltar into the Mediterranean often forms an anticyclonic gyre to the depth of 200 m, and its features are now well documented. A few works based on geostrophic calculations and Bernoulli's equation treat the deep flow. Nine free floats were released at different depths and locations from January to May 1982 and acoustically tracked every 2 hours for 40 to 90 days. Acoustical tracking was done from three listening stations moored in the area. The tracks of the floats at all depths from 220 to 1100 m revealed broad and slow (approximately 2.5 cm/s) cyclonic circulation located under the surface anticyclonic gyre. Part of the flow, following the bottom topography, turned near the Moroccan Continental slope as a jet (approximately 5 cm/s) to Gibraltar and part turned to the east following the southern boundary of the deep channel to the Isle of Alboran.
Ray path identification and acoustic tomography in the Straits of Florida
Authors: Palmer D. R. , Lawson L. M. , Seem D. A. , Daneshzadeh Y.‐H.
Published: February 2008

The Florida Current, which flows through the Straits of Florida, transports a significant fraction of the heat which must be transferred from low to high latitudes in order for the earth to remain in thermal balance. While ocean acoustic tomography is an atttactive candidate for monitoring this heat transport, its use is dependent on being able to identify individual ray paths. All published investigations of tomography have been concerned with deep‐ocean propagation where experience has shown that paths can be identified. Propagation in the Straits is quite different from deep‐ocean propagation, however. The sound speed is such that a ray path which travels modest distances necessarily experiences bottom bounces. It is not clear, a priori, that paths can be identified in the Straits. We report the results of an investigation of this question. Using a fast, specialized ray‐tracing program, we analyzed the fluctuations in ray path geometry resulting from small perturbations in the bathymetry. We found that the topographic features amplify these fluctuations to such a degree that identification of individual rays becomes impossible after only a few bottom bounces. Consequently, there is no adequate interpretive tool for relating an acoustic signal recorded more than a few tens of kilometers from a source to the heat transport, i.e., for carrying out the tomographic inversion. We propose a way of overcoming this identification problem based on the use of acoustic profilers.
Eikonal calculations of short‐wavelength internal‐wave spectra
Authors: Flatté Stanley M. , Henyey Frank S. , Wright Jon A.
Published: February 2008

Following Henyey and Pomphrey (1983), we investigate the spectrum of small‐scale internal waves using the eikonal method. We send test‐wave packets through background internal‐wave shear fields, varying the initial distributions and the background spectra. We find that the test‐wave distributions evolve to Garrett‐Munk wave number spectra for all the cases investigated. We find that the test waves evolve toward higher frequencies, in contrast to a simple induced diffusion model, and consistent with a picture of low‐frequency internal‐wave sources.
An algorithm for retrieval of oceanic wnd vectors from the simulated SASS normalized radar cross‐section measurements
Authors: Gohil B. S. , Pandey P. C.
Published: February 2008

A new algorithm has been proposed to recover wind vectors from the simulated Seasat A satellite scatterometer (SASS) normalized radar cross‐section (NRCS) measurements exploiting the fact that all the dual polarized noise‐free NRCS measurements taken in any azimuth direction should provide the same wind speed in the true direction of wind. The algorithm deals with the computation of wind speeds from SASS NRCS measurements for the entire range of wind direction. The direction for which the standard deviation of wind speeds is minimum, is considered to be the true direction, and the corresponding average wind speed as true speed. The performance of the algorithm is evaluated and compared with the officially adopted SASS‐I algorithm (SA) under noise‐free and noise (standard deviation of 0.13 to 0.40 dB with zero mean) added conditions for wind speeds ranging from 3 to 24 m/s and for all directions from 0° to 360°. When the direction corresponding to the lowest minima of standard deviation of wind speed is taken as true wind direction (case 1), an average improvement of 6.0±1.6% is obtained. When the direction corresponding to the two lowest minima of standard deviation of wind speed, which is closest to the true wind direction, is considered as true wind direction (case 2), an average improvement of 4.0±1.3% is obtained.
The influence of winds and topography on the sea surface temperature patterns over the northern California slope
Authors: Kelly K. A.
Published: February 2008

As part of the Coastal Ocean Dynamics Experiment (CODE), 56 infrared images from the NOAA 6 satellite were analyzed and compared with in situ data to investigate the relationship between SST (sea surface temperature) patterns and winds, topography, and adjusted sea level (ASL) off northern California. After extensive processing to eliminate clouds and to obtain better temperature accuracy, the decimated images were decomposed into mean SST and empirical orthogonal functions (EOF) by using a method developed for a large and gappy set of data. The SST EOF's were compared with EOF's of wind stress and ASL. The first SST mode (in order of variance) described a seasonal warming trend that was somewhat modified by large‐scale wind events. Comparison of the time‐varying amplitudes of SST with those of wind stress and ASL showed that the second and third SST functions described locally driven coastal upwelling that is modified by shelf topography. This analysis suggested that an irregular coastline generates irregular upwelling patterns in response to a spatially uniform wind stress and that the upwelling response propagates northward in conjunction with a northward propagating wind system. Further, the apparent cold‐water sources of the long cold plumes seen in satellite images were shown to be regions of enhanced coastal upwelling associated with capes. These regions extend from the coast across the continental shelf, suggesting that the plumes are anchored to coastal topography.
An extension of Ball's edge wave solution to convex upward topographies
Authors: Shaw Richard Paul , Paskausky David
Published: February 2008

Solutions for edge waves trapped on a concave upward exponential topography (type a) were given by Ball in 1967. This study extends Ball's solutions to convex upward exponential topographies (type b). Similar results are found in terms of eigenmodes, cutoff frequencies, etc., in both cases, but a new phenomenon which was not found in the previous solutions, stopping zones of frequency, is found for the present case. In addition, the group velocity shows far more structure for convex upward exponential topography.
A new technique for monitoring the water vapor in the atmosphere
Authors: Black Harold D. , Eisner Arie
Published: February 2008

In correcting satellite doppler data for tropospheric effects, we have found that we can infer the precipitable water vapor (PWV) at the tracking site. The determination proceeds via a least squares fit of a refraction parameter, along with several others, to each 15‐min pass of data. For its success the technique depends on having (1) an ephemeris for the satellite, (2) an analytic model for the refraction range effect that is good to a few centimeters, (3) doppler (range difference or cycle count) data with a noise level below 10 cm, and (4) a surface pressure/temperature measurement at the tracking site. The PWV is a byproduct of the computation necessary to correct the doppler data for tropospheric effects. We have tried for a number of years to reliably isolate the tropospheric refractive effect in the doppler shift measurement. It is only recently that we have succeeded in doing this. Our success is due to a formulation of the refraction integral that minimizes the necessity for explicit water vapor, temperature, and pressure profiles.
Satellite techniques for determining the geopotential of sea surface elevations
Authors: Pisacane Vincent L.
Published: February 2008

Spaceborne altimetry with measurement accuracies of a few centimeters has the potential for determining sea surface elevations necessary to compute three‐dimensional geostrophic currents from traditional hydrographic observations. The existing limitation in this approach is the uncertainty in our knowledge of the global and ocean geopotentials that produce satellite and geoid height uncertainties about an order of magnitude larger than the goal of about 10 cm. This paper begins with a description of the quantitative effects of geopotential uncertainties on processing altimetry data. This is followed by a review of existing models, which are shown to be inadequate. Potential near‐term improvements not requiring additional spacecraft are discussed. However, even though there would be substantial improvements at the longer wavelength, the oceanographic goal would not be achieved. The potential NASA Geopotential Research Mission (GRM) is described. This mission should produce geopotential models that are capable of defining the ocean geoid to 10 cm and near‐earth satellite positions significantly better. For completeness the state of the art and the potential of Spaceborne gravity gravimetry is described as an alternative approach to improve our knowledge of the geopotential.
Altimeter data and geoid error in mesoscale ocean prediction: Some results from a primitive equation model
Authors: Thompson J. Dana
Published: February 2008

A primitive equation ocean model has been applied to the study of mesoscale ocean dynamics and prediction using sea surface height information derived from a satellite‐borne altimeter. Results from a model of the Gulf of Mexico were directly compared with the altimeter data from GEOS 3 and Seasat reported by Marsh et al. (1984) and in situ hydrographic data analyzed by Maul and Herman (1985). In the eastern Gulf the amplitude and position of relative maxima of sea surface height variability were found to be similar for model, altimeter, and in situ data. In the central Gulf the model and the altimeter‐derived sea surface height variability maps were similar but differed considerably from the in situ results. The mean sea surface in the model and from the in situ data also agreed well in the eastern Gulf, but there was little agreement in the central Gulf. While there is no geoid adequate for determining an independent altimetric estimate of the mean dynamic height of the sea surface in the Gulf by differencing the geoid with the altimeter‐derived mean sea surface, the model dynamic mean sea surface can be subtracted from the mean surface of Marsh et al. (1984) to obtain a new estimate of the Gulf geoid, which may be the best geoid available in that region for several years. A benchmark experiment (“truth”) was integrated to statistical equilibrium and compared with results from four experiments in which the model was initialized with fields modified from archived benchmark data. The experiments differed only in the initialization fields. Each experiment was integrated for 100 days with inflow transport remaining constant throughout the integration. The idealized experiments were initialized geostrophically (1) with the exact sea surface and pycnocline height fields, (2) with only the exact sea surface heights and a pycnocline assumed to compensate it such that the deep pressure perturbations vanished, (3) just as in case 2 but with a geoid error component added on small spatial scales, and (4) just as in case 3 except the geoid error model included an additional contribution in strong geoid gradient regions. The sequence of four numerical experiments showed that (1) geostrophic initialization with exact sea surface and pycnocline height information provided accurate forecasts to 100 days, (2) even when only the sea surface height information was provided to the numerical model for geostrophic initialization and deep pressure perturbations assumed to vanish at the initial time, the forecasts were superior to persistence or climatology over the 100‐day forecast period, and (3) errors in the geoid on spatial scales comparable to the grid resolution of the model did not seriously degrade the forecast, even in dynamically active regions with large gradients in the geoid height where instability processes were observed to occur.
Measurements of ocean wave spectra and modulation transfer function with the airborne two‐frequency scatterometer
Authors: Weissman David E. , Johnson James W.
Published: February 2008

The results of this research show that the directional spectrum and the microwave modulation transfer function (MTF) of ocean waves can be measured with the airborne two‐frequency scatterometer‐microwave resonance technique. By combining two‐frequency backscatter resonance intensity with estimates of the directional wave spectrum (obtained by the airborne surface contour radar) and the known radar beam geometry, it was possible to solve for the unknown MTF using a system equation that has been verified in previous studies. Similar to tower‐based operations, the aircraft measurements of the MTF show that it is strongly affected by both wind speed and sea state. Also detected were small differences in the magnitudes of the MTF between downwind and upwind radar look directions, and variations with ocean wave number. Unexpected results were obtained, which indicate the MTF inferred from the two‐frequency radar is larger than that measured using single‐frequency/wave orbital velocity/Doppler techniques such as tower‐based radars or ROWS (remote ocean wave spectrometer) from low‐altitude aircraft. Possible reasons for this are discussed. When independent MTF data are combined with two‐frequency resonance intensities over a suitable variety of azimuthal look directions, then estimates of the surface wave directional spectrum can be made, to within the accuracy of the uncertainties in the individual data sets.
Short surface waves with growth and dissipation
Authors: Smith Jerome
Published: February 2008

The modulation of surface waves by larger‐scale flows is central to many forms of remote imaging of the sea surface yet is an incompletely understood process. An excellent example is the modulation of short waves by long ones (e.g., by swell). Observed modulations are of the order of 10 times the long‐wave steepness, decrease with both the long‐wave frequency and windspeed, and have stable phase, with maximum short‐wave amplitudes just forward of the long‐wave crests. Assuming a balance between propagation, growth, and drift‐enhanced dissipation, the short‐wave modulations arise owing to (1) direct straining by the long‐wave orbital motion, (2) straining of the wind drift layer (modulating the dissipation rate), (3) variations of the apparent gravity in the short‐wave frame, and (4) induced variations of the applied wind stress (affecting both the short‐wave growth and the drift‐enhanced dissipation). As modeled here, only the last (stress variation) can reproduce the observed wind speed and frequency dependence. In addition, the drift layer and the short waves are closely matched, suggesting direct coupling. The implied fractional modulation of stress is of the order of 20 times the long‐wave steepness.
Aspects of warm rings in the Gulf of Mexico
Authors: Vukovich Fred M. , Crissman Bobby W.
Published: February 2008

Various aspects of warm rings in the Gulf of Mexico were derived from satellite infrared data and Ship‐of‐Opportunity data. After the warm rings separate from the Loop Current, they move into the western Gulf of Mexico. It was shown from 12 years of data (1973 through 1984) that there are three characteristic paths of movements of the rings: a northern path, a mid‐Gulf path, and a path that takes the rings into the southern extremities of the western Gulf of Mexico. It was shown that all three paths eventually lead the ring to a region in the northwestern portion of the western Gulf of Mexico (the area defined by 25°N to 28°N and 93°W to 96°W). As the rings move from the eastern Gulf to the western Gulf, the speed of the ring was observed to oscillate. The oscillation is over a speed range from 1 to 8 km per day, on the average, and the period varies from 40 to 100 days. The average speed of the ring was 5 km per day. After the ring separates from the Loop Current, the surface area of the ring decreases to about 55 percent of its initial size in approximately 150 days and to about 31 percent of its initial size in about 300 days.
Weddell‐Scotia Sea marginal ice zone observations from space, October 1984
Authors: Carsey F. D. , Holt Benjamin , Martin Seelye , McNutt Lyn , Rothrock D. A. , Squire V. A. , Weeks W. F.
Published: February 2008

Imagery from the shuttle imaging radar‐B experiment as well as other satellite and meteorological data are examined to learn more about the open sea ice margin of the Weddell‐Scotia Seas region. At the ice edge, the ice forms into bandlike aggregates of small ice floes similar to those observed in the Bering Sea. The radar backscatter characteristics of these bands suggest that their upper surface is wet. Further into the pack, the radar imagery shows a transition to large floes. In the open sea, large icebergs and long surface gravity waves are discernable in the radar images.
Nonlinear coupling between surface temperature and ocean upwelling as an agent in historical climate variations
Authors: Gaffin Stuart R. , Hoffert Martin I. , Volk Tyler
Published: February 2008

Global temperature records extending about 100 years into the past display interannual fluctuations of a few tenths °C on a variety of time scales. A number of previous model simulations have employed anthropogenic CO2 warming, solar variability, and volcanic aerosol loading as external forcings to account for major features of these records. We develop a simple system using a one‐dimensional, upwelling‐diffusion world ocean model that incorporates a nonlinear linkage between the global surface temperature and the large‐scale oceanic overturning. Interesting dynamic behavior was discovered, in particular, internal self‐excited oscillations with parameter‐dependent periods of the approximate order of a hundred years exhibiting surface temperature changes of the order of ±0.5°C. The largest features of the northern hemispheric surface land temperature record can be simulated with our climate and deep ocean feedback formulation and CO2 forcing alone. One would conclude that internal processes of this type can indeed produce temperature changes as powerful and as rapid as those produced by the above mentioned external forcings, and our results indicate that more work is needed on the role of nonlinear coupling between surface temperature and ocean dynamics in transient climate models.
Intermediate‐scale wave motion in shallow water shear current
Authors: Zheng Quanan , Yeli Yuan
Published: February 2008

Intermediate‐scale shear waves are ubiquitous in the world's ocean. They are the horizontal wavy movement along the shear interface having a typical wavelength of 100 km. Based on a simple theoretical model using the standard shallow water geophysical fluid dynamic equation, we found that these phenomena can be modeled by a kind of stable shear wave triggered by external forces, such as wind stress. Our results indicate that their amplitudes should be directly proportional to the wind stress, and the relationship between the phase speeds of the waves and their wave numbers can be expressed by a parabolic equation. Comparisons between theoretical results and data derived from the satellite IR images show good agreement.
Thermohaline fronts and baroclinic flow in the Argentine basin during the austral spring of 1984
Authors: Roden Gunnar I.
Published: February 2008

Thermohaline fronts, structure, and baroclinic flow in the central Argentine basin are investigated on the basis of a 1984 field experiment. The Brazil Current, after initial overshoot, meanders northeastward toward subtropical latitudes with speeds of the order of 0.3 m s−1. The meanders have a wavelength of about 400 km and an amplitude of 200 km. Brazil Current signatures, as expressed by dynamic height, are recognizable to depths of several kilometers. The Brazil and Antarctic Circumpolar currents do not meet in the central Argentine basin to form common eastward flow, as was expressed in classical descriptions, but instead diverge sharply near 42°W. This is seen also in the trajectories of satellite‐tracked drifters. The region between the currents is marked by cyclonic and anticyclonic eddies. Strong thermohaline fronts accompany the boundaries of these currents. The Brazil Current and subantarctic fronts are well separated in the central basin. Brazil Current density fronts are deep and extend from the surface to 3000 m, while the associated temperature and salinity fronts are intermittent over this depth interval. Temperature fronts virtually vanish at the interface between the Antarctic Intermediate Water and the North Atlantic Deep Water. Salinity fronts reverse their polarity beneath the core of the former. At depths between 3000 and 4000 m, abyssal temperature and salinity fronts are observed which are largely density compensating. At the subantarctic and cold core eddy fronts, horizontal temperature and salinity gradients in the upper mixed layer compensate each other in such a way that no density front is found. Deep subpycnocline mixed layers occur in the poleward lobes of the Brazil Current during austral spring, suggestive of previous winter convection.
Low‐frequency sea surface temperature and wind variations over the Indian and Pacific oceans
Authors: Blazejewski H. , Cadet D. L. , Marsal O.
Published: February 2008

The wind and temperature fields over the Indian and Pacific oceans have been analyzed to study the coupling between the two oceans on the time scale of the Southern Oscillation. The analysis shows the propagation of zonal wind anomalies from the western Pacific Ocean toward the date line together with the displacement of a pool of warm water. There is some indication of a zone of convergence over the equatorial Indian Ocean. The results seem to rule out a direct propagation of a signal from the Indian Ocean toward the Pacific Ocean, as the signal in the former ocean lags that in the latter.
Near‐surface current and temperature variability observed in the equatorial Atlantic from drifting buoys
Authors: Reverdin G. , McPhaden M. J.
Published: February 2008

We examine data from 23 surface drifters which were deployed between June 1983 and July 1984 at 4°W, 1.5°–4°S. The drifters were equipped with a window shade drogue centered at 15‐m depth and in most cases a 117‐m‐long thermistor chain. Drift data indicate a westward South Equatorial Current with typical speeds of about 20 cm s−1 south of the equator. Maximum westward flow of 30–40 cm s−1 occurred in June through September of 1983 and 1984, consistent with climatology. Near‐zero westward flow, which was significantly weaker than was expected from climatology (by about 20 cm s−1), occurred from February to April, 1984. This probably represents real interannual variability and may be related to the fact that the equatorial Atlantic was warmer than usual in the spring and summer of 1984. Energetic variations on time scales of O(1 month) and less and space scales of O(100 km) and less are ubiquitous in the drift and temperature data. Kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s−2, with slightly higher values in boreal summer. Energy levels north of the equator are about 500 cm2 s−2 on the basis of data available only during the boreal summer and fall. The sources of this energy include inertia‐gravity waves, instabilities of the general circulation, and other phenomena for which there is no simple explanation.
Warm outbreaks of the Gulf Stream into the Sargasso Sea
Authors: Cornillon Peter , Evans David , Large William
Published: February 2008

A warm outbreak is a large body of Gulf Stream water with apparent anticyclonic circulation that detaches from the Gulf Stream and exists as a well‐defined entity in the Sargasso Sea. Because warm outbreaks are warmer at the surface than Sargasso Sea water, they are often clearly visible in satellite thermal infrared imagery. From a survey of over 750 satellite images covering the Sargasso Sea immediately to the south of the Gulf Stream between 64° and 74°W and spanning a 5‐year period, 18 possible outbreaks have been observed. All formed west of 65°W, with the majority forming between 67° and 72°W. Five of the 18 were observed to detach completely from the Gulf Stream and have the following properties in common: (1) they all formed in several days at or near the point of maximum cyclonic curvature of a large Gulf Stream meander, (2) the surface expression was relatively short‐lived, of the order of 10 to 20 days, and (3) their dimensions (and those of the other 13) were of the order of 100 by 200 km. Given the similarity between the characteristics of warm outbreaks and those of “opposite vortices” predicted by Ikeda and Apel (1981) from a two‐layer, quasi‐geostrophic model of an eastward flowing jet, it is suggested that the two phenomena are related. Further support of this hypothesis is the fact that the rate of formation of warm outbreaks, between two and six per year, is similar to that of anticyclonic eddies observed in expendable bathythermograph surveys of this area.
Variability of net longwave radiation over the eastern North Pacific Ocean
Authors: Siegel D. A. , Dickey T. D.
Published: February 2008

The net longwave radiation at the sea surface (LW↑↓) was measured over the eastern North Pacific Ocean for 22 days during the fall of 1982. These measurements were made from the R/P FLIP as part of the Optical Dynamics Experiment. The mean LW↑↓ emitted from the sea surface was 52.0 W/m2 with a variance of 802.6 W2/m4. The largest fraction of the variance was observed to be in the diurnal frequency band. LW↑↓ and the total cloud amount exhibited significant diurnal cycles (amplitudes of 13.5 W/m2 and 7%, respectively) which were negatively correlated. LW↑↓ measurements were compared with values obtained from seven different bulk formulas for LW↑↓ in order to evaluate their predictive capabilities. These formulas predict less than 45% of LW↑↓ variance, indicating that these methods are inadequate for the description of LW↑↓ variability. Statistical predictions were made using linear hindcastors to examine the relationships between LW↑↓ and other surface meteorological and oceanographic parameters. The signs and magnitudes of the arbitrary coefficients in the linear hindcastors are consistent with hypotheses used for a conceptual model of radiant heat transfer between two parallel gray plates through an interacting medium. The highest predictive skill levels (54.3–55.3% of the variance explained) occur for the case of a two component linear hindcastor where both the cloud layer and the water vapor concentration above the sea surface are taken into account. The success of the statistical predictions indicates that the fundamental physics relevant to LW↑↓ variability are incorporated in the conceptual parallel plate model.
Eastern Pacific Ocean circulation near the onset of the 1982–1983 El Niño
Authors: Mangum L. J. , Hayes S. P. , Toole J. M.
Published: February 2008

Over a 1‐month period (October 5 to November 6, 1982) during the initial stages of the 1982–1983 El Niño, hydrographic and velocity profiling measurements were made in the eastern equatorial Pacific by two research vessels. Track lines approximated a square, centered near the Galápagos Islands with approximately meridional sections at 95°W and 85°W and nearly zonal sections at about 5°N and 5°S. Water mass characteristics and estimated currents of these sections are discussed. Sea surface temperature nearly everywhere was warmer than 25°C (an anomaly of 2°C–3°C). The equatorial thermocline, represented by the 20°C isotherm, was depressed by nearly 50 m at 85°W and more than 100 m at 95°W relative to a historical mean profile. Across 95°W, estimated geostrophic (relative to 500 dbar) and directly measured near‐equatorial velocity profiles indicated significant eastward surface flow. The South Equatorial Current south of the equator had disappeared. Estimated warm water transport (σt < 24.5 kg m−3) indicated an influx into the region which was approximately that required to balance the observed low‐frequency sea level change at the Galápagos Islands. Temperature and salinity properties as well as the transport estimates indicated that this warm water came predominantly from the west.
Off‐equatorial influence upon Pacific equatorial dynamic height variability during the 1982–1983 El Niño/Southern Oscillation event
Authors: Pazan Stephen E. , White Warren B. , Inoue Masamichi , O'Brien James J.
Published: February 2008

Anomalous sea level, anomalous observed dynamic height (0/400 dbar) and anomalous model dynamic height are compared at the locations of 13 island sea level stations in the tropical Pacific for each 2‐month interval of the 4‐year period 1979 to 1982. Sea level compares well with both observed dynamic height (0/400 dbar) based on temperature/depth observations made by volunteer observing ships, and model dynamic height derived from a linear two‐layer wind‐driven model. The cross correlation between sea level and either of the dynamic heights is generally greater than 0.75. The ratio of root‐mean‐square (Rms) differences about the mean annual cycle of the sea level to Rms differences of either of the dynamic heights is approximately unity. Starting in 1981, off‐equatorial Rossby wave activity propagated toward the western boundary of the Pacific basin; this also occurred in model dynamic height both north and south of the equator. Yet neither sea level observations nor observed dynamic height has the spatial and temporal resolution to establish a connection between the off‐equatorial Rossby wave activity and the equatorial Kelvin wave activity in the western boundary region. On the other hand, the model dynamic height does have this capability. Therefore at the western boundary, the model Rossby wave activity is found to have excited coastally trapped Kelvin‐Munk wave activity, which transmitted the anomalous sea level equatorward. At the equator this model coastally trapped wave activity excited eastward propagating equatorial Kelvin waves, yielding a pair of anomalous peaks in dynamic height variability in the eastern equatorial Pacific associated with the 1982–1983 El Niño/Southern Oscillation (ENSO) event. The evolution of these two peaks in anomalous dynamic height associated with the 1982–1983 ENSO event is examined at eight locations in the tropical and equatorial Pacific, The major peak originated in the off‐equatorial South Pacific and coincided with the wintertime 1982–1983 El Niño event in the eastern equatorial Pacific. The secondary peak originated in the off‐equatorial North Pacific and coincided with the anomalous peak which occurred in the eastern equatorial Pacific the summer before the 1982–1983 ENSO event.
Comparison of surface currents measured by HF Doppler radar in the western Florida Straits during November 1983 to January 1984 and Florida Current transports
Authors: Schott Friedrich A. , Frisch Shelby A. , Larsen Jimmy C.
Published: February 2008

An evaluation of surface currents measured by HF radar during November 29, 1983, to January 31, 1984, with radar sites at Jupiter and Stuart on the Florida east coast is carried out in comparison with currents and transports measured by moorings and submarine cable. While an earlier analysis of currents measured in summer 1983 with radars located at Palm Beach and Jupiter (Schott et al., 1985) found significant northward shear in the northward radar currents about 20 km offshore leading to concerns about a possible bias in the radar currents, this effect was not observed in the second application farther north. It is possible that the shear in the summer 1983 field might have been real and related to the topography in the southern part of the 1983 radar field where no intercomparison current data had been available. Concerning the usefulness of radar currents as Florida Current transport indicators, which was the prime intention of their application in the context of the Subtropical Atlantic Climate Studies, this second study finds much more encouraging results than the one based on the observations of summer 1983. While the first study was inconclusive because only small transport fluctuations occurred during the summer 1983 observation period, this second study finds significant correlation. Florida Current transport fluctuations had a total range of 15 × 106 m3/s during the second observation period, and correlation with downstream radar currents, averaged zonally across the center of the radar field, was 0.85. Coherence was significant for periods longer than 5 days. Highest correlation with transport was found for radar currents farthest out, to the right of the axis of the stream.
Data sensitivities of sea ice drift and ocean stress in North Atlantic high latitudes
Authors: Walsh John E. , Plummer David W. , Herman Gerald F. , Ross Becky , Raymond William H.
Published: February 2008

Experiments with a limited‐area objective analysis are used to determine the effects of various data sources on surface stress and sea ice drift in North Atlantic high latitudes during a 7‐day period of the First GARP Global Experiment (FGGE). The objectively analyzed fields provide the input to a planetary boundary layer model, which provides the surface wind stresses for the forcing of a dynamic‐thermodynamic sea ice model. Different combinations of drifting buoy, surface marine, and satellite sounder data are deleted from the FGGE level IIB data input. On individual days the stresses are found to differ by as much as 50–100% and the ice drift speeds by as much as 10–15 km d−1 when buoy reports are deleted from the observing network. Seven‐day mean differences of the ice drift speeds are 3–5 km d−1 in some regions. The deviations from the “complete data” results are larger when both buoy/marine and satellite data are deleted than when only one type is deleted. While the high‐latitude sensitivities to satellite data are generally smaller than to buoy/marine data in the period considered here, large differences in ocean surface stress occasionally result from subtle effects of satellite data on the static stability of the near‐surface region. The results also show how data sensitivities can be exaggerated by the imposition of data rejection criteria in experiments utilizing consistent sets of guess fields and input data. The ice velocities obtained from the various experiments are compared with the available buoy displacements and with changes in the ice edge deduced from the Navy/NOAA weekly ice analyses.
Thermal structure along 4°W in the Gulf of Guinea during 1983–1984
Authors: Houghton Robert W. , Colin Christian
Published: February 2008

SEQUAL/FOCAL data from 4°W derived from conductivity, temperature, and depth, expendable bathythermograph, and aircraft‐deployed expendable bathythermograph sections and moored thermistor time series are combined to investigate the thermal structure in the Gulf of Guinea for 1983 and 1984. The equatorial and coastal upwellings, as defined by vertical isotherm displacements, have the same magnitude for both years. The seasonal upwelling extends to at least 300 m depth with the signal at depth leading the surface. The equatorial upwelling occurs approximately 6 weeks earlier in 1983 than in 1984, while the coastal upwelling is only 2 weeks earlier in 1983. The meridional structure of the upwelling is approximately symmetric about the equator at depth but becomes asymmetric, shifted to the south, near the surface. During early 1984 the thermocline is anomalously deep, nearly 30 m below the climatic mean. Because of distinct interannual differences in the wind field it is possible to identify the influence of local and far‐field wind forcing on the thermal structure. The main annual “summer” equatorial upwelling is forced primarily by the zonal wind stress distributed westward across the ocean basin. The increasing asymmetry about the equator in the eastern Gulf of Guinea suggests the influence of the local meridional wind stress. The coastal upwelling is coupled to the Guinea Current. The anomalously deep thermocline that persisted in early 1984 is the result of both local and far‐field changes in the zonal wind stress.
Seasonal estimates of global oceanic whitecap coverage
Authors: Erickson David J. , Merrill John T. , Duce Robert A.
Published: February 2008

Seasonal estimates of oceanic whitecap coverage are presented on global contour maps. The instantaneous fraction of the sea surface covered by whitecaps as a function of wind speed has been described previously using a power law fitting technique [Monahan and Muircheartaigh, 1980]. This relationship, coupled with a Gaussian wind speed frequency distribution, allows us to calculate the oceanic whitecap coverage accounting for the variance about mean wind speeds. We use monthly mean wind speed and variance information in 5° latitude × 5° longitude areas over the world ocean to estimate the global oceanic whitecap coverage distribution. The whitecap coverage in the northern hemisphere oceans displays a substantial seasonal dependence. The boreal summer average whitecap coverage in the high‐latitude North Atlantic is about 0.5% and increases by a factor of roughly 6 to over 3.0% for a boreal winter average. The whitecap coverage in the high‐latitude southern hemisphere oceans exhibits only a factor of 3 difference for the same seasons, from about 1% in the austral summer to over 3% for the austral winter. There are several high‐latitude areas with greater than 3% average whitecap coverage over several months of the year. The monsoonal winds in the Indian Ocean result in over 3% mean whitecap coverage for the June‐July‐August period.
Barotropic flow of a warm‐core ring from seafloor electric measurements
Authors: Lilley F. E. M. , Filloux J. H. , Bindoff N. L. , Ferguson I. J. , Mulhearn P. J.
Published: February 2008

A seafloor array of recorders spanning the Tasman Sea has measured the electric field signature of a major warm‐core ring embedded in the East Australian Current. Theory for motional electromagnetic induction allows the electric measurements to be interpreted in terms of barotropic water velocity. Water transport and kinetic energy estimates thus obtained show a concentration of mesoscale activity near the Australian coast. The total circulation of the particular ring is estimated to be of the order of 100 Sv.
Relaxation from upwelling in the Coastal Ocean Dynamics Experiment
Authors: Send Uwe , Beardsley Robert C. , Winant Clinton D.
Published: February 2008

A relaxation of the upwelling system on the northern California shelf occurs when upwelling‐favorable winds decay or reverse. Observations from the Coastal Ocean Dynamics Experiment are used to investigate this process, with emphasis on the near‐surface temperature evolution. Models of relaxation warming are tested for the surface layer (0–30 m) over midshelf, with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior. Onshore advection of the upwelled isopycnal field is a relatively unimportant contribution. The warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes, warmest inshore and in the south of the experimental area. These patterns appear to be related to a topographic influence of Point Reyes, possibly through the generation of gradients in the wind field. Remote advection of warm water from as far south as San Francisco occasionally occurs as well. The nature of the relaxation mechanism has general implications. A new warm, saline, nutrient‐rich water mass may be formed in the surface layer. Since the warming processes are not the reverse of the cooling, an important asymmetry is present. It causes time‐variable upwelling to generate conditions very different from steady upwelling: a new upwelling front is created during each event, with upwelled water seaward of it, and reversed alongshelf flow contributes to the warming and exchange mechanisms. The system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer.