bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation of wave height distribution
Authors: Thornton Edward B. , Guza R. T.
Published: February 2008

The transformation of random wave heights during shoaling, including waves breaking in the surf zone, was measured with an extensive array of instruments in the field. The initially Rayleigh height distributions in 10‐m depth were observed to be modified by shoaling and breaking into new distributions which are again nearly Rayleigh but with some energy loss. Using locally measuredHrms, the Rayleigh distribution describes the measured central moments ofH1/3andH1/10with average errors of −0.2% and −1.8%, respectively. The Rayleigh distribution is used to describe the random nature of wave heights in a single‐parameter transformation model based on energy flux balance. The energy losses associated with wave breaking are parameterized using observed breaking wave distributions coupled with a periodic bore dissipation model. Using incident waves measured in 10‐m depth as input conditions, the model predictsHrmsat shoreward locations within a rms error of ±9%. The single free parameter of the model, a constantBrepresenting the fraction of foam on the face of a wave, was chosen to best fit the data. The resulting large value ofBimplies that the simple periodic bore dissipation function substantially underestimates the actual dissipation.
Production rate of airborne sea‐salt sulfur deduced from chemical analysis of marine aerosols and precipitation
Authors: Várhelyi G. , Gravenhorst G.
Published: February 2008

On the basis of a thorough compilation of the results of measurements of marine aerosols and precipitation, the total sulfur deposition into the oceans is estimated to be 180–350 Tg S yr−1. From this amount, 120–250 Tg S yr−1 is attributed to sea‐salt sulfur, while 60–100 Tg S yr−1 is attributed to ‘excess sulfur’ By assuming that 10% of the produced sea salt is transported onto the continents, it is concluded that the annual production rate of sea‐salt sulfur is about 130–275 Tg S yr−1, several times higher than those fluxes used in the global sulfur budgets up to now.
The function and response of an improved stratospheric condensation nucleus counter
Authors: Wilson J. C. , Hyun J. H. , Blackshear E. D.
Published: February 2008

An improved condensation nucleus counter (CNC) for use in the stratosphere is described. The University of Minnesota CNC (UMCNC) has a sequential saturator and condenser and uses n‐butyl alcohol as the working fluid. The use of a coaxial saturator flow, with aerosol in the center and filtered, alcohol‐laden air around it, speeds the response of this instrument and improves its stability as pressure changes. The counting efficiency has been studied as a function of particle size and pressure. The UMCNC provides an accurate measure of submicron aerosol concentration as long as the number distribution is not dominated by sub 0.02 μm diameter aerosol. The response of the UMCNC is compared with that of other stratospheric condensation nucleus counters, and the results of a (near) comparison with a balloon‐borne condensation nucleus counter are presented. The UMCNC has operated 14 times on a NASA U‐2 aircraft at altitudes from 8 to 21.5 km.
Solar variability in the spectral range 2350–2870 Å
Authors: Hall L. A.
Published: February 2008

Between April 1977 and April 1981, four balloon flights of a solar ultraviolet spectrometer were made to altitudes near 40 km in the stratosphere. Analysis of these measurements shows that the solar irradiance in the wavelength range 2350–2870 Å has been constant within ±7% over this period. The central emission cores of the Mg II resonance lines increased in intensity by about 20% over the same time period.
Interannual variations of global total ozone revealed from Nimbus 4 BUV and ground‐based observations
Authors: Hasebe Fumio
Published: February 2008

An objective analysis is made by the hybrid use of Nimbus 4 BUV and ground‐based network data to investigate interannual variations in global distributions of total ozone. Much improvement in spatial resolution and reliability of the analysis is attained. From the deduced time changes in 7 years (April 1970 to May 1977), the quasi‐biennial and 4‐year oscillations (QBO and FYO) are separated by numerical filtering. Characteristic features of these oscillations are investigated by examining time changes of global patterns as well as some spatial mean values. The QBO in total ozone is characterized by large variabilities in time and space. Typical features are as follows: In the tropics, positive deviations nearly coincide with the westerly phase of equatorial zonal wind at 50 mbar. Zonally uniform phase changes exhibiting cross‐equatorial northward propagation are observed. Phase propagation is continuous to northern mid‐latitudes, where the ozone distributions are accompanied by zonal wave number 3–4 disturbances. In northern high latitudes, deviations superposed by wave number 1 distribution are found often opposite to mid‐latitudes. In the southern hemisphere, the phase is reversed around 15°S and nearly out‐of‐phase relation to northern mid‐latitudes is observed. Wave number 1 is the dominant wave component through‐out the southern hemisphere. The FYO in total ozone is suggested as a global phenomenon. This oscillation is characterized as follows: A roughly symmetric distribution with respect to the equator is observed with the out‐of‐phase relation between tropics and extratropics. There also appears a phase propagation starting from southern high and mid‐latitudes and reaching northern high latitudes. Zonally uniform phase changes with wave number 3 disturbances are seen in the northern mid‐latitudes. In the equatorial region and southern hemisphere, systematic phase precedings in the western hemisphere are observed. For both QBO and FYO, planetary scale total ozone waves of zonal wave number 1 in the winter hemisphere are seen to penetrate into the summer hemisphere.
Comparison of airborne CO2 flask samples and measurements from the Mauna Loa Observatory during the HAMEC Project (June 1980)
Authors: Herbert G. A. , Harris T. B. , Chin J. F. S.
Published: February 2008

During June 1980, the Hawaii Mesoscale Energy and Climate Project (HAMEC) field program was conducted in the vicinity of the island of Hawaii. The objective of the program was to use the NOAA P3 aircraft to measure meteorological variables upwind and downwind of the island to provide data to evaluate mesoscale models of airflow and cloud physics. One specific objective was to obtain flask samples upwind of the island to confirm that the CO2 values observed at the Mauna Loa Observatory (MLO) are representative of the free air at comparable altitudes. On 2 days, carbon dioxide flask samples were exposed aboard the aircraft at the altitude of the observatory and immediately above the trade inversion. Flask pairs in reasonable agreement were obtained on both occasions. During the same period the sampling conditions at MLO were free of obvious local contamination. The average difference between the aircraft measurements at the altitude of the observatory and the continuous CO2 record from the observatory over the same period of time was 0.8 mole fraction in ppm. Differences in the individual measurements are discussed with respect to prevailing meteorological conditions.
Short waves on long waves
Authors: Kenyon Kern , Sheres David , Bernstein Robert
Published: February 2008

Spatial changes in the wavelength and direction of short‐wavelength surface gravity waves, caused by their interaction with much longer wavelength gravity waves, are calculated by applying geometrical optics to the short waves in the reference frame that reduces the long waves to a steady current, which is horizontally variable but unidirectional. The wave rays are very nearly parallel to the direction of the current. Along a ray the wavelength and the angle between the propagation direction of the short waves and the ray direction are both maximum at the long wave troughs (where the steady current speed is maximum) and minimum at the crests (where the current speed is minimum), whether the short waves travel with or against the long waves. The short waves can never be reflected by the long waves. The calculated magnitudes of the wavelength and direction changes of the short waves are valid for arbitrary surface slope of both short and long waves, assuming no wave breaking occurs. Therefore these results are more general than any known ones, but they agree with earlier work when all wave slopes are taken small compared to unity and the wave number directions of the short and long waves are parallel.
Definite integral of the product of hermite functions, with applications to the theory of nonlinear interactions among equatorial waves
Authors: Ripa P.
Published: February 2008

An analytic expression and an asymptotic estimate are derived for the definite integral of a product of Hermite functions (i.e., a Hermite polynomial times a Gaussian). The argument of each Hermite function is proportional but not neccesarily equal to the integration variable. The asymptotic estimate is used to show that the integral is negligible unless there are points where the sum of the local wave numbers is zero. This result is used, in the context of geophysical fluid dynamics, to establish a connection between the meridional interaction condition for equatorial waves, represented by Hermite functions, and midlatitude waves, represented by sinusoids: for the latter it is the sum of the constant wavenumbers that has to vanish
Seasonal variation of methane flux from a California rice paddy
Authors: Cicerone R. J. , Shetter J. D. , Delwiche C. C.
Published: February 2008

To allow increased understanding of the global budget of atmospheric methane, individual methane sources require investigation. We have measured methane emissions from a California rice paddy during the entire 1982 growing season. A very strong seasonal dependence was observed. Methane emissions were highest in the last 2–3 weeks before harvest; daily emissions reached 5 g CH4/m2. Over the 100‐day season, daily emissions averaged about 0.25 g CH4/m2, higher than our previously reported values. Attempts to estimate global rice paddy emissions must recognize the possibility of seasonal variations. Soil temperature at 10‐cm depth correlated poorly with our measured fluxes; soil redox potential was a more reliable indicator.
Comment on “Evidence for a solar cycle signal in tropospheric winds” by G. D. Nastrom and A. D. Belmont
Authors: Venne D. E. , Nastrom G. D. , Belmont A. D.
Published: February 2008

In a previous paper it was suggested that a substantial 11‐year period solar cycle influence may exist in tropospheric wind and temperature data. The current study reanalyzes a subset of the original data with the intent of better assessing the significance of the reported correlations. Extensive use is made of empirical testing; also employed is a maximum entropy spectral analysis. The new findings indicate that the correlations between the 10.7 cm solar flux and 300 mbar winter winds are not statistically significant. An upper limit on the percentage of variance in these winds explainable by a solar cycle influence is suggested to be ∼8%
An example of meteorological effects on the Alboran Sea Gyre
Authors: Bucca Paul J. , Kinder Thomas H.
Published: February 2008

Following a period of weak winds, an air‐dropped expendable bathythermograph (AXBT) survey on July 4, 1980 showed the Alboran Sea Gyre clearly present at 100‐m depth but not at the surface. Winds on July 5 and 6 were from the west at >12 m/s, and both AXBT temperature distributions and satellite images then showed the gyre clearly dominating the temperature structure both at 100 m and at the surface. The disparity between the surface and 100‐m temperature patterns on July 4 demonstrates that caution must be used when interpreting satellite imagery in the Alboran Sea (which has been used by several investigators as representing the gyre's structure). The change in the shallow temperature distribution from July 4 to 6 is opposite to what some investigators have proposed as the normal response of the gyre to atmospheric forcing.
Satellite observations of circulation in the eastern Bering Sea
Authors: Paluszkiewicz Theresa , Niebauer H. J.
Published: February 2008

Satellite infrared observations of the eastern Bering Sea shelf and basin were analyzed from December 1979 to August 1981. A region of warm surface water which extends from the Gulf of Alaska through the Aleutian Passes into the Bering Sea was observed coincident with a band of warm surface water and with eddies along the shelf break. The spatial and temporal relationships of these patterns imply a surface inflow through Unimak and other western Aleutian Passes, flow along the shelf break including eddies along the Bering Slope Current, and cyclonic flow in the basin. The proposed generating mechanisms for eddies along the shelf break include topographic interactions, baroclinic instabilities, and Rossby waves.
Longshore structure of infragravity wave motions
Authors: Holman R. A. , Bowen A. J.
Published: February 2008

Synchronous runup records were collected from 14 locations spaced irregularly over a 7 km stretch of a low‐slope beach. The significant runup height, herein defined as the significant vertical excursion of water level at the shoreline, was typically 2 m, 60% of the incident significant wave height at the breakpoint. The runup spectra were dominated by the energy at low frequencies, with 99.9% of the variance in motions with periods longer than 20 s and 83% for periods longer than 50 s. A peak between 0.005 and 0.010 Hz was present in all spectra. Analysis of this band showed the motion to be a standing edge wave with wavelength between 5 and 10 km and significant edge wave height at the antinode of 1.3 m, accounting for half of the local significant runup height. The edge wave period was approximately 140 s and the mode number in the range 3–7. An apparently linear sand bar was present 175 m offshore, roughly the same location as the first node of cross‐shore velocity for the edge wave. While the edge wave could not have been the cause of the bar (a standing edge wave does not create a linear bar), the opposite may be true, with the bar potentially providing a topographic resonance. As the local head‐lands extend only a small fraction of the offshore distance of the edge wave, they are unlikely to be significant reflectors. The single rip current observed occurred at the edge wave node.
Turbulent wave boundary layers: 1. Model formulation and first‐order solution
Authors: Trowbridge John , Madsen Ole Secher
Published: February 2008

Oscillatory turbulent flow produced near a rough seabed by linear surface waves is analyzed. An analogy to the wall region of steady turbulent flow is shown to be valid very near the bed and provides the basis for a model in which the eddy viscosity is the product of a vertical length scale and the first two Fourier components of a shear velocity based on the instantaneous, local bed shear stress. With this time‐varying eddy viscosity model, an approximate closed‐form solution for the boundary layer flow is obtained. Comparison with available laboratory measurements indicates that the eddy viscosity does in fact vary with time and that the theoretical approach taken here is physically sound. The effect of a time‐varying viscosity on quantities of practical interest is found to be potentially important.
Simulation of the mixed layer at OWS November and Papa with several models
Authors: Martin Paul J.
Published: February 2008

The Mellor‐Yamada level‐2 and 2 1/2, Niiler, and Garwood one‐dimensional mixed‐layer models were compared for some simple forcing experiments and were tested by simulating changes in the mixed layer at ocean stations November and Papa for the year 1961. The ocean station simulations show that the models can be tuned to give fairly good results. However, the need to readjust model constants when changing locations suggests that there is room for improving some of the mixing parameterizations. The sensitivity of the model simulations to certain “external” parameterizations, including surface heat flux, seawater turbidity, and ambient diffusivity below the mixed layer, was investigated. The year‐long simulations were found to be very sensitive to the seawater turbidity. Increasing the turbidity from Jerlov optical type I to type III causes a maximum increase in the monthly mean SST at November of 3°C or more. The simulations are most sensitive to seawater turbidity during summer when the mixed‐layer remains shallow. For the ambient diffusivity a decrease from 0.4 to 0.01 cm2/s results in a maximum increase in the monthly mean SST at November and Papa of 0.5 and 1.5°C, respectively. The effects of using a constant ambient diffusivity are most noticeable in late summer when the seasonal thermocline is strongest. The effects are larger at Papa than at November because of the stronger summer seasonal thermocline at Papa. Best results at November and Papa were obtained by using the observed optical water types (I and II, respectively) and relatively small values for ambient diffusivity (less than 0.2 cm2/s).
Methods for making point estimates of eddy heat flux as applied to the Antarctic Circumpolar Current
Authors: Nowlin W. D. , Worley S. J. , Whitworth T.
Published: February 2008

Yearlong measurements of current and temperature are used to examine the characteristics of eddy heat flux and its distribution in Drake Passage. This seemingly straightforward calculation can produce misleading results when measurement errors are not corrected and when careful consideration is not given to the nature of the time series under study and the coordinate system used. When moorings blow over during periods of high current speeds, eddy heat fluxes produced from the resulting records may be overestimated by as much as 20% if not corrected by using concomitant pressure time series and vertical temperature gradients. Although short‐time‐scale processes (such as tides, internal waves, and inertial oscillations) are routinely eliminated from heat flux estimates by low‐pass filtering, low‐frequency contamination of eddy heat fluxes is not usually considered. Long‐period events can impose unwanted, dominating cross correlation (eddy heat flux) between fluctuation temperature and velocity. In Drake Passage, low‐frequency variability in some current records is associated with sporadic lateral shifts of the fronts within the Antarctic Circumpolar Current. Defining an effective eddy time scale (40 hours to 90 days) and band‐passing the current records before calculating eddy heat flux results in values that are more homogeneous (consistent with one another) in direction and have higher statistical significance. Finally, we consider the coordinate system used for the eddy heat flux calculations relative to the dynamic processes under study. For the Circumpolar Current we define “poleward” eddy heat flux as that component perpendicular to the axis of the current that forms a continuous, but distorted, band encircling Antarctica. Since the current direction varies in time, across‐stream eddy heat flux is calculated relative to the 90‐day low‐pass direction. The resulting heat fluxes from all deep instruments are small (about 1 kW/m2), whereas those at depths less than 1000 m in the northern passage are an order of magnitude larger. The average across‐stream flux for all available instruments is 3.7 kW/m2 and directed to the right (poleward) of the 90‐day low‐pass current. Cospectra of fluctuation temperature and velocity show that heat flux is separated, on the average, into two frequency bands with corresponding periods between 100 and 40 days and 16 and 10 days. This pattern is strongly influenced by the records from shallow instruments and those in the northern passage and compares favorably with the cospectrum from a 5‐year bridged record from the central passage. Comparison with previous estimates in this region shows considerable differences, partly as a result of the use of different techniques. However, analysis of five 1‐year records from a single location shows that interannual variability is large, which urges caution when interpreting the significance of isolated short‐term estimates of eddy heat flux.
Dye diffusion experience in the Texas bays: Low‐wave conditions
Authors: Ward George H.
Published: February 2008

Measurements of diffusion from slug releases of fluorescent dye performed in the bays of Texas are compiled along with attendant hydrographic and hydrometeorological data. These data sets are confined to conditions of low surface wave activity to better expose the effects of local currents on diffusion. Development of a dye patch is parameterized in terms of a lateral diffusivity, which measures “turbulent” diffusion, and a longitudinal dispersion, which measures the effect of vertical shear in the current. The former is found to follow a local 4/3‐power dependence upon scale and has a noisy correlation with current speed. The latter is found to be consistent with a theoretical model predicting a variation with the square of current speed and inverse variation with the squared Chézy coefficient. These data are considered to be generally representative of the shallow lagoon environment typical of Gulf of Mexico bays.
An intense cyclonic eddy east of the Mozambique Ridge
Authors: Gründlingh Marten L.
Published: February 2008

Data from cruises of the Meiring Naudé in 1978 delineated an intense cyclonic eddy in the vicinity of 30°S, 38°E and extending to a depth of more than 1800 m. Between May and June 1978 the eddy advected to the southeast at 5 cm s−1. The eddy was elliptical (90×240 km), and the volume transport varied between 20 and 48×106 m3 s−1.
On resolving vertical modes with observational data
Authors: Hayes S. P. , Ripa P. , Mangum L. J.
Published: February 2008

A least squares regression formulation is developed to study the expected errors in the coefficients of a modal expansion of observational data. Given an empirical or theoretical vertical mode number energy spectrum and assuming that certain modes (signal) are to be resolved and that the remaining modes (noise) are a contamination, then there exists an optimum set of weights which will minimize the expected errors of the signal modal amplitudes. These expected errors, as well as those associated with any other set of weights, can be evaluated and the adequacy of a given array determined. Examples from the equatorial Pacific Ocean are used to show the utility of this technique and to explore several existing or possible measurement arrays.
The two‐degree discontinuity as explained by boundary mixing
Authors: Minster Jean‐Francois
Published: February 2008

A three dimensional description of the two‐degree discontinuity (TDD) in the North Atlantic western basin is made from the TTO and 1981 North Atlantic section data. In 1981 this break in the θ‐S slope of the Atlantic deep waters is found at θ = 1.90°C, S = 34.895‰, near the western flank of the basin, and it seems to follow an isopycnal at σ4 = 45.89‰. It encounters the western boundary at the level of the Western Boundary Undercurrent (WBUC). Based on nutrient data, the TDD is more sharply defined along the western flank of the basin than along the Mid‐Atlantic Ridge, where the TDD water is fresher and colder and where one finds more Antarctic Bottom Water (AABW) above the discontinuity. The TDD is consistent with vertical mixing being dominantly a boundary process: along the western flank of the basin, upward mixing of AABW is stopped at the WBUC level by the strong southward flow of North Atlantic Deep Water (NADW). Along the ridge, boundary mixing allows AABW to mix upward with waters from shallower levels.
Parameterization of wind‐stress coefficients over water surfaces
Authors: Wu Jin
Published: February 2008

At all fetches under various wind velocities the wind‐stress coefficient is related to the nondimensional fetch gL/Uz2 (g is the gravitational acceleration, L the fetch, and Uz the wind velocity measured at elevation z, which increases with both wind velocity and fetch). A unique relationship was found between the wave age and nondimensional fetch; the former can therefore be used as an alternate parameter for the latter, this is especially useful for the open sea.
Wind effects on a front over the continental shelf slope
Authors: Ikeda Motoyoshi
Published: February 2008

A continuously stratified, two‐dimensional (vertical and seaward) model is used to study the effects of alongshore wind on a front between lighter water over the continental shelf and heavier water in the offshore ocean. The model produces three components of alongshore flows: one component associated with the horizontal density front and two wind‐driven components, one near the coast and one over the shelf break. The cross‐shore circulation has two near‐surface features; a seaward component resulting from the offshore density gradient and a shoreward (seaward) component resulting from the right‐hand (left‐hand) alongshore wind stress, which has the coast to the right (left), facing downstream. These two components contribute to the maintenance of the front. With no wind, low‐density water over the shelf tends to move toward the offshore ocean associated with the near‐surface seaward flow, resulting in flatter isopycnal surfaces. A moderate right‐hand alongshore wind suppresses the density‐driven surface flow and constrains the shelf water, while a strong wind in the same direction pushes the front shoreward and makes isopycnal surfaces steeper, resulting in increased exchange of the shelf water. A left‐hand alongshore wind contributes to more rapid frontal relaxation and a seaward shift in its position. These results are applied to the Labrador Shelf.
Retrieval of sea surface temperatures from HIRS2/MSU
Authors: Susskind J. , Reuter D.
Published: February 2008

The methods used at the Goddard Laboratory for Atmospheres (GLA) to retrieve sea surface temperatures from HIRS2/MSU data for the last 2 months of the NASA sea surface temperature intercomparison workshop are described. Results are shown that compare anomaly fields produced by using data from ships, AVHRR, and HIRS2/MSU for these months. Monthly mean fields derived from AVHRR and HIRS2 data show roughly comparable statistical accuracy compared to ship fields. Errors in the HIRS2 fields appear more random, while AVHRR data have larger regionally dependent biases and show large area spatially coherent errors. The random errors in the HIRS2 fields should be further reduced by performing the retrievals at a higher spatial resolution.
Salinity intrusion in the Eastmain River estuary following a major reduction of freshwater input
Authors: Lepage S. , Ingram R. G.
Published: February 2008

On July 19, 1980, 80% of the runoff of Eastmain River, a subarctic shallow estuary, was diverted into the La Grande River for hydroelectric development. Consequent to the diversion, the estuary, which had been mostly salt‐free, was subjected to a gradual saltwater intrusion along a 10‐km section in its lower reaches. The adjustment of the salinity regime to a new quasi‐steady state took place over a period of about 40 days. The circulation field reached a new quasi‐equilibrium within 8 days. The 2‐month interval following the river diversion, termed the transition period, was analyzed in terms of both time and space modifications of the circulation and salinity fields. A one‐dimensional finite difference explicit scheme numerical model was applied to the estuary as a complement to observational data. Good agreement was obtained between the model results and the low‐frequency current meter observations of salinity and longitudinal velocity. These results showed that the salinity intrusion was primarily governed by tidal dispersion.
Ice banding as a response of the coupled ice‐ocean system to temporally varying winds
Authors: Häkkinen Sirpa
Published: February 2008

In this study we model formation of ice bands in the marginal ice zones. A one‐dimensional coupled ice‐ocean model is used in which the ice model is coupled to a reduced gravity ocean model through interfacial stresses. The internal ice stresses are important only at high ice concentrations (90%–100%); otherwise, the main balance for the ice motion is between the air‐ice stress and the ice‐water stress, i.e., free drift. The drag coefficients were chosen so that the air‐ice momentum flux is 3 times greater than the air‐ocean momentum flux. Thus the Ekman transport is larger under the ice than in the open water, so that winds parallel to the ice edge, with the ice on the right, produce upwelling. The upwelling simulation was extended to include temporally varying forcing, which was chosen to vary sinusoidally with a 4‐day period. This forcing resembles successive cyclone passings perpendicular to the ice edge. When the oceanic upper layer was thin, which means that the dynamics are strongly nonlinear, the ice bands were formed. The up/downwelling signals do not disappear in wind reversals because of nonlinear advection. This leads to convergences and divergences in oceanic and ice velocities that manifest themselves as ice banding. At least one wind reversal is needed to produce one ice band.
On Gulf Stream meander characteristics near Cape Hatteras
Authors: Tracey Karen L. , Watts D. Randolph
Published: February 2008

From 1979 to 1982, Gulf Stream path fluctuations within 375 km downstream of Cape Hatteras, North Carolina, have been monitored by inverted echo sounders. Histograms of the north wall locations along four cross‐stream sections change shape and increase in range dramatically downstream through the study area: Near Cape Hatteras, the histogram is peaked with the Gulf Stream found over half of the time within a narrow 10‐km range. The distributions become progressively more symmetric and the ranges widen downstream such that in the eastern portion of the study area the Gulf Stream can be found with equal probability throughout its 145‐km excursion range. From the 36‐month‐long time series near 73°W there is evidence of a seasonal cycle of Gulf Stream positions; northerly locations occur in the summer/fall, when transports are lower, and southerly locations occur in the winter/spring, when transports are higher. An observational dispersion relationship is presented for meander propagation and growth: Downstream propagation rates increase smoothly from about 14 km d−1 for meanders with periods and wavelengths (33 days, 460 km) to over 45 km d−1 for the (4 days, 180 km) meanders. Meander amplitudes show rapid growth rates in two separate bands, near (4–5 days, 180–230 km) and (10–33 days, 300–500 km).
Wind‐driven upwelling in the vicinity of Cape Finisterre, Spain
Authors: McClain Charles R. , Chao Shenn‐Yu , Atkinson Larry P. , Blanton Jack O. , De Castillejo Frederico
Published: February 2008

Observations and numerical simulations of upwelling along the Galician coast of Spain during April 1982 are presented. In situ measurements include shipboard determinations of hydrographic and biological parameters from a grid of stations covering the continental shelf from Cape Finisterre to Ria de Vigo, sea level data from Vigo and La Coruña, and wind stress estimates derived from the ship winds and from surface pressure charts. Sea surface temperature information and pigment concentration information have been obtained from a sequence of satellite images from the NOAA 7 advanced very high resolution radiometer and the Nimbus 7 coastal zone color scanner, respectively. Since the Cape Finisterre sector of the Iberian peninsula is characterized by an abrupt change in coastline orientation, wind‐driven upwelling can occur in that region over a 270° range of wind direction. These data document the evolution of upwelling and the resultant coastal circulation in response to two wind events that occurred over a 10‐day period. Salient features of the circulation include a southward coastal jet and a northward flow further offshore along the western coast. Numerical simulations of the coastal currents, the vertical excursion of a density interface from a static equilibrium position, and coastal sea level are conducted using a wind patch characterized by constant direction and negative curl. The simulations show that during these wind events, the greatest upwelling will occur either at Cape Finisterre or along the northern coast as was observed in this case and as has been reported by others. It is suggested on the basis of the analysis of the sea level records and on the numerical simulations that wave disturbances propagate northward along the coast at a speed of 120–160 km/day. Finally, it is speculated that much of the organic material formed during upwelling events north of the Cape Finisterre is advected out to sea northwest of the cape.
A cyclonic eddy and shelf‐slope water exchange associated with a Gulf Stream warm‐core ring
Authors: Churchill James H. , Cornillon Peter C. , Milkowski George W.
Published: February 2008

Warm‐core ring (WCR) 83D passed through a linear array of moored temperature, conductivity and velocity sensors during October 1983. Satellite‐derived thermal imagery combined with data from the moored sensors have revealed a cold‐core cyclonic eddy, of approximately 80‐km diameter, traveling in advance of ring 83D. This cyclone, whose angular momentum magnitude was about 1/3 that of the WCR, evolved either during or shortly after the WCR's formation. Hydrographic and moored sensor data suggest that the WCR brought about a subsurface exchange of shelf and slope water, with near‐surface slope water moving onshore and near‐bottom shelf water being drawn offshore and around the ring. Examination of 308 cross‐shelf hydrographic sections from the Middle Atlantic Bight has indicated that such exchange commonly occurs in the presence of a WCR. This apparent ring‐induced exchange may significantly affect the overall salt balance of Middle Atlantic Bight shelf water. As an example, the volume of slope water within a well‐surveyed intrusion, which lay onshelf of WCR 79B, was 16% of Wright's (1976) estimate of the annual slope water transport to the Middle Atlantic Bight shelf.
Simulation of pollutant transport in homogeneous coastal zones with application to Lake Ontario
Authors: Murthy C. R. , Simons T. J. , Lam D. C. L.
Published: February 2008

On the basis of extensive current measurements in Lake Ontario near Pickering, empirical impulse response functions have been obtained which permit computation of coastal currents in this region from routine wind observations at Toronto Island Airport. The model may be expected to simulate about 75% of the variance of the actual currents in this region and to produce very reliable indications of alongshore current directions and reversals. The empirical model for coastal currents has been combined with a stochastic dispersion model using microcomputer technologies to predict the behavior of contaminant spills in the nearshore zone of Lake Ontario. The model has been verified with the thermal effluent data collected near the Pickering Nuclear Power Generating Station.
Seasonal variation of cross‐equatorial flow in the Somali Current
Authors: Schott Friedrich
Published: February 2008

Moored current measurements in the Somali Current on the equator of approximately 1‐year duration reveal a seasonal cycle of the vertical current structure which is substantially different during part of the year from that previously perceived from measurements in the boundary current away from the equator. In particular, during the winter monsoon the southwestward flow at the surface reaches down only to little more than 100 m, while a northward countercurrent exists below down to 400 m. Observed current structure is quite well reproduced by a numerical model with high vertical and reasonable horizontal resolutions. Overall conclusions are that the equatorial and off‐equatorial circulation of the Somali Current are separate systems during most of the year and that remote forcing from the east along the equator appears to be a minor effect in the seasonal variability of near‐surface flow in the equatorial Somali Current.
A satellite time series of sea surface temperatures in the eastern equatorial Pacific Ocean, 1982–1986
Authors: Legeckis Richard
Published: February 2008

Satellite measurements of sea surface temperature (SST) in the eastern equatorial Pacific have been made since 1982 using the multichannel advanced very high resolution radiometers on NOAA polar orbiting satellites. A 4‐year data set has been accumulated at weekly intervals and a spatial resolution of about 50 km on an interactive computer system. The time lapse evaluation of the data reveals annual and interannual variations of the SST which are related to the 1982–1983 El Niño and Southern Oscillation as well as to coastal and equatorial upwelling events. The El Niño was preceded by a weak equatorial cooling pattern from May to August 1982. The subsequent equatorial warming persisted until June 1983. From mid‐1983 to early 1984, the equatorial SST pattern was dominated by pronounced upwelling and westward advection of cold water by the South Equatorial Current. North of the equator the zonal equatorial SST front was distorted by a succession of westward moving equatorial long waves which extended nearly to the date line. During both 1984 and 1985 the equatorial upwelling began to intensify during May and lasted until the following February. The transition to seasonal equatorial warming occurred from February to March and was marked by abrupt increases of SST on time scales of less than 1 week. The zonal equatorial SST fronts disappeared at this time, but the upwelling off the coast of South America persisted. From December to April of each year, short‐term upwelling events appeared intermittently along the western coast of Central America south of the Gulf of Tehuantepec and southwest of Lake Nicaragua and the Gulf of Panama. These upwelling events were weak from 1982 to 1984 and were more intense during 1985 and 1986. During February and March of 1985, an extreme case of upwelling was observed south of the Gulf of Panama. The SST was depressed by at least 9°C, and cooler water appeared to be advected southwestward to the equator and the Galapagos Islands. Time series of the sea surface temperatures at fixed locations and color images of the SST distribution are used to illustrate these events.
Further development of an improved altimeter wind speed algorithm
Authors: Chelton Dudley B. , Wentz Frank J.
Published: February 2008

A previous altimeter wind speed retrieval algorithm was developed on the basis of wind speeds in the limited range from about 4 to 14 ms−1. In this paper, we use a new approach which gives a wind speed model function applicable over the range 0 to 21 ms−1. The method is based on comparing 50 km along‐track averages of the altimeter normalized radar cross section measurements with neighboring off‐nadir scatterometer wind speed measurements. The scatterometer winds are constructed from 100 km binned measurements of radar cross section and are located approximately 200 km from the satellite subtrack. The new model function agrees very well with earlier versions up to wind speeds of 14 ms−1 but differs significantly at higher wind speeds. We discuss the relevance of these results to the Geosat altimeter launched in March 1985.
A stochastic model for wind‐driven currents over the continental shelf
Authors: Brink K. H. , Chapman D. C. , Halliwell G. R.
Published: February 2008

A stochastic model for current, pressure, and density fluctuations over the continental shelf and slope is solved for coherence, phase, and gain between the oceanographic variables arid wind stress. Comparison of wind stress spectra and transfer functions show that free coastal‐trapped wave physics tends to exist in a frequency band bounded at the low end because of frictional predominance and at the high end because of the absence of wind energy at appropriate alongshore length scales. The transfer functions for density and especially cross‐shelf velocity show that these variables are sensitive to short length scales in the forcing and are thus difficult to predict in general. Model results are compared to observations of bottom pressure and alongshore velocity from the 1982 Coastal Ocean Dynamics Experiment off northern California. The results agree with observations, at least qualitatively, with regard to spatial and frequency patterns in coherence and gain. The poorest point of agreement is in the amplitude of wind stress‐current gains, which the model systematically underpredicts. The comparisons do demonstrate the importance of including accurate representations of bottom friction and of both cross‐shelf and alongshore gradients of wind stress amplitude.
On the ratio of the mixing coefficients of heat and salt of Antarctic Bottom Water in the North Atlantic
Authors: Whitehead J. A.
Published: February 2008

Values of vertical eddy salt diffusivity and heat diffusivity for Antarctic Bottom Water were estimated by Whitehead and Worthington (1982) from both current meter results and geostrophic calculations. The ratios of the diffusivities have one impossible value of 0.858 for water colder than 1.1°C potential temperature for the geostrophic results. This could be evidence against the geostrophic results. However, a small interpolation error in their Tables 5 and 6 was uncovered. The corrected ratio is 1.01, which is possible, although very close to 1, and one other ratio is 0.98. Thus geostrophic calculations cannot be ruled out, but they lead to ratios very close to 1.
Seasonal cycle of velocity in the Atlantic North Equatorial Countercurrent as measured by surface drifters, current meters, and ship drifts
Authors: Richardson P. L. , Reverdin G.
Published: February 2008

This report describes the general circulation and seasonal variation of currents in the equatorial Atlantic, concentrating on the North Equatorial Countercurrent (NECC), using data collected as part of the Seasonal Response of the Equatorial Atlantic and Programme Français Océan et Climat dans l'Atlantique Equatorial experiments plus historical ship drifts. During 1983–1985 the Lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the North Equatorial Countercurrent and 23 in the South Equatorial Current (SEC). In addition, continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the NECC, at 6°N, 28°W. These measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal, meridional, and vertical structure. The seasonal cycle of the NECC is very regular from year to year. Each year the NECC starts up in May–June. It flows eastward across the Atlantic with surface speeds of up to 143 cm/s in the west, extending down to 350 m at 28°W, and flowing into both the Guinea Current and North Equatorial Current. It disappears or reverses from about January–June west of 18°W. Some near‐surface water of the NECC is inferred to downwell and flow equatorward toward the Equatorial Undercurrent. The SEC flows into the North Brazil Current, which during spring continues up the coast into the Caribbean. During fall, however, the whole North Brazil Current retroflects, or turns back on itself, between 45° and 50°W, forming the western NECC. The retroflection establishes a meander pattern in the NECC that slowly propagates westward during fall at a speed of 4 cm/s. The meanders have a displacement of about 300 km in latitude, a wavelength of 900 km, and meridional velocity fluctuations of up to 100 cm/s. The swift currents and time‐dependent meanders in the western NECC cause a high eddy kinetic energy, ∼2400 cm2/s2, equivalent to that of the energetic part of the Gulf Stream.
Multisensor comparison of ice concentration estimates in the marginal ice zone
Authors: Burns B. A. , Cavalieri D. J. , Keller M. R. , Campbell W. J. , Grenfell T. C. , Maykut G. A. , Gloersen P.
Published: February 2008

Aircraft remote sensing data collected during the 1984 summer Marginal Ice Zone Experiment in the Fram Strait are used to compare ice concentration estimates derived from synthetic aperture radar (SAR) imagery, passive microwave imagery at several frequencies, aerial photography, and spectral photometer data. The comparison is carried out not only to evaluate SAR performance against more established techniques but also to investigate how ice surface conditions, imaging geometry, and choice of algorithm parameters affect estimates made by each sensor. Active and passive microwave sensor estimates of ice concentration derived using similar algorithms show an rms difference of 13%. Agreement between each microwave sensor and near‐simultaneous aerial photography is approximately the same (14%). The availability of high‐resolution microwave imagery makes it possible to ascribe the discrepancies in the concentration estimates to variations in ice surface signatures in the scene.
An observation of the planetary boundary layer in the marginal ice zone
Authors: Kellner G. , Wamser C. , Brown R. A.
Published: February 2008

Aircraft measurements at the marginal ice zone (MIZ) during a cold air outbreak are presented together with shipborne observations in the Fram Strait. These investigations were done during the Marginal Ice Zone Experiment in June and July 1984. The determined profiles, variances, and fluxes are discussed for different flight legs oriented parallel and normal to the ice edge. The data reveal a significant change in the turbulent momentum, heat, and moisture fluxes as the flow crosses the ice edge. The CD10 based on aircraft fluxes and surface winds were ≈2.9 × 10−3 over the MIZ and ≈2.0 × 10−3 over the nearby ocean. The variance spectra exhibit a clear shift in the peak frequency from about 1 Hz over ice to 0.4 Hz over water, which corresponds to an increase of the characteristic scale from 100 to 250 m. Secondary peaks appear in the low‐frequency range, indicating the development of secondary flows in the mixed layer over the ocean.
The role of floe collisions in sea ice rheology
Authors: Shen Hayley H. , Hibler William D. , Leppäranta Matti
Published: February 2008

A collisional rheology for an idealized two‐dimensional flow of a fragmented ice field is derived. This fragmented ice field is modeled as an assembly of identical smooth disks. Collisions between neighboring disks are caused by the mean deformation field. These collisions transfer momentum which produces the internal stresses in the deforming ice field. By equating the collisional energy losses to the deformational energy, a relationship between the stress and strain rate is quantified. To demonstrate the essential idea, an analytical derivation is first given under quite restricted assumptions. A Monte Carlo simulation is then developed to provide a more general approach for the analysis. It is found that the collisional stresses are proportional to the square of disk diameter and the square of the deformation rate. The magnitude of stresses is also found to increase rapidly as the collisional restitution of disks increases, the collisional rheology yields zero tensile strength. The associated normal flow rule commonly used in the plastic rheology is not valid in the collisional rheology. It is found that the collisional stresses are very small. Consequently, the resulting stress divergence is estimated to be much lower than the air stress typically encountered in the marginal ice zone. However, these collisional stresses become singular as the maximum compactness is reached, indicating that a different mechanism may exist in that extreme.