bluuebunny/crossref_metadata_2025 huggingface dataset:
A cool anomaly off northern California: An investigation using IR imagery and in situ data
Authors: Rienecker Michele M. , Mooers Christopher N. K. , Hagan Denise E. , Robinson Allan R.
Published: February 2008

Satellite IR imagery and in situ hydrographie data are used to understand better the mesoscale variability of the California Current system and to explore the relation of its surface and subsurface thermal structures. In August 1982, one of the cool filaments commonly seen in satellite IR images during summer off Northern California was sampled hydrographically during an OPTOMA (Ocean Prediction Through Observation, Modeling, and Analysis) cruise. Based on the cool anomaly seen in a series of IR images and the in situ hydrographie data, and based on geostrophic calculations, a jet entrained upwelled coastal water and advected it rapidly through the warmer waters offshore, providing an important cross‐shore transfer process. The anomaly was about 50 km wide and extended vertically to about 40 m. The temperature patterns at the surface were well correlated with those to about 30 m; below 50 m, the surface temperature was better correlated with horizontal temperature gradients, i.e., the “thermal wind”, consistent with strong horizontal advection by the geostrophic jet. The cool anomaly was also relatively dense. Based on investigation of the T‐S properties, the coastal water had been diluted through mixing with Columbia River plume water on the northern edge of the anomaly. Near the temperature front, in the shoreward sampled portion of the anomaly, and just south of the anomaly, interleaving occurred. There was also a surface saline anomaly embedded in the cool anomaly near the temperature front. The location of the temperature front in the in situ data and in the IR imagery corresponded well. The temperature front was tracked in a series of IR images over 2 weeks. The reorientation of the seaward extremity of the anomaly, from westward to northwestward, and the southwestward displacement of its southern boundary at speeds of 2 to 5 km/d were consistent with the propagation of mesoscale features evident in successive quasi‐synoptic surface dynamic topography maps. The southwestward displacement was probably also related to surface Ekman transport.
Gulf Stream meanders: Observations on the deep currents
Authors: Johns W. E. , Watts D. R.
Published: February 2008

During 1979–1980, an array of inverted echo sounders (IES) and three deep current meter moorings were deployed on the continental slope 100–200 km northeast of Cape Hatteras, North Carolina. This array continuously monitored the path of the Gulf Stream and the deep currents under it. The mean currents at two sites 1000 m off the bottom near the northern edge of the stream were veered to the right of the mean surface path, indicating a deep inflow to the stream. Mean currents 500 and 1000 m off the bottom 50 km farther offshore were northeastward, nearly colinear with the surface Gulf Stream path. The deep velocity fluctuations are characterized by a transition from transverse flow aligned with the local bathymetry for periods longer than about 12 days to fluctuations with a cross‐stream orientation for shorter periods. For periods between 4 days and 1 month, cross‐stream movements of the Gulf Stream temperature front are vertically coherent and nearly barotropic, based on correlations between the IES‐measured stream path and deep temperature fluctuations. Temperature fluctuations at the current meter sites lead cross‐stream (positive onshore) velocity fluctuations by approximately 90°. Consideration of the nondiffusive fluctuating heat equation for deep layers suggests a three‐term balance between local rate of change, cross‐stream horizontal advection, and vertical advection of temperature, with the first two being of like sign. Kinematically, this requires |wTz| > |υTy|, so that parcel trajectories in the cross‐stream plane are inclined at angles steeper than the mean cross‐stream slope of the isotherms. Eddy energy conversion between the fluctuations and the mean field in deep layers is predominantly baroclinic, with e‐folding growth time scales of approximately 10 days.
The effect of water temperature and synoptic winds on the development of surface flows over narrow, elongated water bodies
Authors: Segal M. , Pielke R. A.
Published: February 2008

Simulations of the thermally induced breeze involved with a relatively narrow, elongated water body is presented in conjunction with evaluations of sensible heat fluxes in a stable marine atmospheric surface layer. The effect of the water surface temperature and of the large‐scale synoptic winds on the development of surface flows over the water is examined. As implied by the sensible heat flux patterns, the simulation results reveal the following trends: (1) When the synoptic flow is absent or light, the induced surface breeze is not affected noticeably by a reduction of the water surface temperature; (2) for stronger synoptic flow, the resultant surface flow may be significantly affected by the water surface temperature.
Upper‐ocean velocity structure of Gulf Stream warm‐core ring 82B
Authors: Joyce T. M. , Kennelly M. A.
Published: February 2008

Acoustio Doppler current profiling of warm‐core ring (WCR) 82B revealed changes in the velocity structure over much of the ring's 7‐month lifespan. As ring diameter decreased, peak speeds in the high‐velocity region decreased from 0.8 m s−1 in April 1982 to 0.5 m s−1 in August 1982. Azimuthally averaged velocities revealed the core of WCR 82B to be in near solid‐body rotation, with little measurable horizontal divergence at 100 m. In addition, potential vorticity was conserved in the ring core despite interactions with the Gulf Stream and large changes in ring size. Deviations from symmetry in WCR 82B were caused by superposition with the shelf‐slope front, small cyclonic eddies, and upper‐layer mean flow.
Macrozooplankton biomass in Gulf Stream warm‐core rings: Spatial distribution and temporal changes
Authors: Wiebe Peter H. , Flierl Glenn R. , Davis Cabell S. , Barber Valerie , Boyd Steven H.
Published: February 2008

The vertical and horizontal distribution of macrozooplankton biomass was measured at four time points in warm‐core ring 82B. Samples were also collected in two other warm‐core rings, the Slope Water, nine cold‐core rings, and the Sargasso Sea. Biomass in newly formed warm‐core rings was 1.5–2 times lower than that of the surrounding Slope Water but increased within 3–4 months to levels found in the adjacent waters, a rate 4 times faster than the biomass in cold‐core rings reaches levels found in the Sargasso Sea. A mixing model is used to show that for the period March through June the increase in biomass at the center of ring 82B was largely the result of in situ production. Half of the macrozooplankton biomass in the upper 1000 m of warm‐ and cold‐core rings, the Slope Water, and the Sargasso Sea was usually below 200 m at night and 300 m by day. Biomass shoaled during periods of high concentrations of near‐surface plant biomass associated with spring restratification of the upper ocean. Diel vertical shifts in median biomass depth in the upper 1000 m showed significant regional differences; the order of the values averaged for all cruises was ring 82B = 76 m < Slope Water = 115 m < cold‐core rings = 149 m < Sargasso = 212 m.
Fine structure and mixing at the edge of a warm core ring
Authors: Ruddick Barry R. , Bennett Andrew S.
Published: February 2008

Observations of temperature and salinity fine structure near the edge of a newly formed Gulf Stream warm‐core ring are presented. A thermohaline front and a cold tongue of shelf water were tracked for about 16 km in a series of crossings by a depth‐cycling CTD. The core was observed to become warmer, saltier, and more dense in the downstream direction, leading to estimates of eddy diffusivities larger than 10−3 m2/s. It is concluded that fluxes this large cannot be due to double‐diffusive processes, either lateral or vertical. Shear‐driven turbulence can account satisfactorily for the mixing of the core, but it would require that the Richardson number be near 1/4, which is much smaller than that estimated from thermal wind.
High‐frequency Doppler radar measurements of the Florida Current in summer 1983
Authors: Schott F. , Frisch A. S. , Leaman K. , Samuels G. , Fotino I. Popa
Published: February 2008

An oceanographic evaluation is carried out here of high‐frequency (HF) Doppler radar measurements of surface currents made by the NOAA Wave Propagation Laboratory June 26 to August 4, 1983, at the western side of the Florida Straits in the area between Jupiter and West Palm Beach in the context of the Subtropical Atlantic Climate Studies. These current measurements are compared with direct current measurements made at various positions in the area covered by the radar, and investigated for their potential as transport indicator. Means and standard deviations of the downstream current component compared well with those from PEGASUS and subsurface moored current measurements carried out in the northern part of the radar current field up to 35 km distance from the coast, but there seemed to exist a bias in the southern part of the current field measured by the radar, causing significant northward mean shear about 20 km offshore. Low‐frequency current fluctuations from the radar currents and near‐surface moored currents were coherent for the downstream but not the small cross‐stream component. Mean downstream components in a center strip of the radar current field, where data quality was found to be best, were compared with Florida Current transports as determined by cable and by moored current measurements, but transport fluctuations were small during the measurement period which fell into the summer maximum of the Florida Current. Coherence with cable transports was significant at the meander time scale of 5 days, but a longer period transport burst of 3×106 m3/s occurring during the time period was not identified in the surface current measurements. In summary, the HF radar as used in this application is useful to determine near‐surface patterns of eddies and meanders but doubtful for derived quantities like energy fluxes and vorticity without additional calibration.
Kelvin wave fronts, Rossby solitary waves and the nonlinear spin‐up of the equatorial oceans
Authors: Greatbatch Richard J.
Published: February 2008

This paper examines the spin‐up from rest of an equatorial ocean with meridional boundaries following the sudden onset of spatially uniform winds by using a nonlinear, one‐active‐layer, reduced‐gravity shallow‐water model. It is shown that the results obtained can differ considerably from corresponding integrations with a linear model and that this occurs within realistic parameter ranges. In the westward wind case a Kelvin wave front can develop, across which there is a discontinuity in the zonal current and in the depth of the model pycnocline. A vortex pair resembling a Rossby solitary wave as described theoretically by Boyd (1980b) is generated by the impact of this front on the eastern boundary. In the eastward wind case a series of equatorial Rossby solitary waves is generated at the eastern boundary. An extension of Boyd's theory is given that allows for a background zonal current and is used to account for the westward propagation speed of these waves. An important effect of nonlinearity in this case is to prevent equatorial waves from being able to bring to rest the equatorial (Yoshida) jet that is established during the first stage of the integration. The model response is shown to depend on the values of only two parameters, one of which (X) measures the nonlinearity and the other (δ) the ratio of the equatorial Rossby radius to the longitudinal basin width L. The former parameter varies as the product of L and the surface wind forcing and as the inverse square of the linear gravity wave speed. It is known that there is a threshold value of X (Xcrit) for the sharp Kelvin wave front to occur. It is shown that the results presented here for a nonlinear, one‐active‐layer, reduced‐gravity shallow‐water model are of relevance to a continuously stratified ocean model, provided there is a thermocline‐trapped mode that is dominantly excited by wind forcing, such as the second baroclinic mode in the equatorial oceans.
The ocean's response to a CO2‐induced warming
Authors: Bryan Kirk , Spelman Michael J.
Published: February 2008

The climate response to a large increase in atmospheric CO2 was investigated in a numerical experiment with a coupled ocean‐atmosphere model. The study is focused on one aspect of the experiment, the predicted response of the ocean to the warming episode. A fourfold increase in atmospheric CO2 causes a warming sufficiently intense to produce a partial collapse of the thermohaline circulation of the ocean. Surprisingly, the wind‐driven circulation of the ocean is maintained without appreciable change. The global hydrological cycle intensifies without a major shift of the pattern of net precipitation over the model ocean. In the warming episode the downward pathways for heat, which include diffusion and Ekman pumping, remain open. The partial collapse of the thermohaline circulation closes the normal upward pathways associated with abyssal upwelling and high‐latitude convection. As a result the thermocline is able to sequester almost twice as much heat than would be predicted from the behavior of a neutrally buoyant tracer introduced at the surface under normal climatic conditions. An enhanced sequestering of heat would produce a negative feedback for greenhouse warming. However, the partial collapse of the thermohaline circulation found in the numerical experiment would also affect the global carbon cycle, possibly producing a climatic feedback as strong as that caused by an enhanced uptake of heat from the atmosphere.
Vertical diffusion in meromictic Powell Lake, British Columbia
Authors: Sanderson Brian , Perry Karen , Pedersen Tom
Published: February 2008

Simple diffusion models are developed to describe vertical diffusion in Powell Lake, a meromictic former fjord containing trapped seawater. Measurements of the vertical distribution of chlorinity are used to determine the dependence of vertical diffusivity on depth. Near the bottom of the lake the vertical diffusivity is about 4 times that of the molecular diffusivity of salt. On this basis, ions with different molecular diffusion coefficients will be lost from the bottom of the lake at different rates, which partially explains differences observed in the ratios of concentrations of ions in saline bottom water from ratios characteristic of seawater. The observed increase in temperature with depth is shown to result from the geothermal heat flux through the lake's bottom.
Diurnal cycling: Observations and models of the upper ocean response to diurnal heating, cooling, and wind mixing
Authors: Price James F. , Weller Robert A. , Pinkel Robert
Published: February 2008

Measurements made from R/P Flip using rapid profiling conductivity, temperature, and depth probes and vector‐measuring current meters provide a new and detailed look at the diurnal cycle of the upper ocean. A diurnal cycle occurs when solar heating warms and stabilizes the upper ocean. This limits the downward penetration of turbulent wind mixing so that air‐sea fluxes of heat and momentum are surface trapped during midday. The central problem is to learn how the trapping depth DT (mean depth value of the diurnal temperature and velocity response) is set by the competing effects of wind mixing and surface heating. In this data set the diurnal range of surface temperature
was observed to vary from
, with most of the day‐to‐day variability attributable to variations of wind stress τ. Wind mixing causes a pronounced asymmetry of the Ts response by limiting the warming phase to only about half of the period that the surface heat flux Q is positive. The associated wind‐driven current, the diurnal jet, has an amplitude of typically
, with no obvious dependence upon τ. The diurnal jet accelerates downwind during the morning and midday. It is turned into the wind by the Coriolis force during early evening and is often erased by the following morning. Under the assumption that wind mixing occurs as an adjustment to shear flow stability, a scaling analysis and a numerical model study show that the daily minimum trapping depth
goes like τ/Q1/2. It follows that
goes like Q3/2/τ and that
goes like Q1/2. These results, as well as the simulated time dependence of the diurnal cycle, are at least roughly consistent with the observations. The observed time‐averaged velocity profile has a spiral shape reminiscent of the classical Ekman spiral. However, its structure is a consequence of diurnal cycling, and its parameter dependence is in some ways just opposite that of the Ekman model; e.g., increased wind stress may cause decreased vertical shear between fixed levels in the upper ocean.
Long‐term in situ calculations of kinetic energy and Reynolds stress in a deep sea boundary layer
Authors: Gross Thomas F. , Williams Albert J. , Grant William D.
Published: February 2008

Long‐term measurements of Reynolds stress and kinetic energy are necessary to characterize the bottom boundary layer during storms which transport sediment in the High Energy Benthic Boundary Layer Experiment area on the Nova Scotia Rise. The benthic acoustic stress sensor current meter system employed an on‐board microcomputer to process 2‐Hz velocity vector data into 20‐min averages of velocity vectors and the turbulent Reynolds stress tensor. The data indicate a bottom boundary layer, which is usually transitional, with bottom roughness scaling between viscous (z0 = v/9u*) and rough (z0 = ks/30). During the periods of transitional flow the logarithmic layer was not a useful indicator of boundary stress. Direct stress and energy measurements showed that the stress was much less than that indicated by the slope of the transitional mean logarithmic velocity profile. Several westward high‐velocity events, which were modulated by a significant tidal component, were recorded. It appears from this data set that the mean westward flow must be accompanied by a train of internal tidal waves to achieve the velocities necessary to be the sediment transport events identified as “benthic storms”.
Isotopic and micrometeorological ocean CO2 fluxes: Different time and space scales
Authors: Smith Stuart D. , Jones E. Peter
Published: February 2008

Clarifications of the interpretation of the CO2 eddy flux measurements of Smith and Jones (1985) are offered in the context of criticisms by Broecker et al. (this issue). Downward pumping of CO2 and other atmospheric constituents by the pressurization of air entrained by breaking waves is considered to be a plausible mechanism. Apparent discrepancies between short‐term “eddy flux” surface exchange rates and longer‐term isotopic determinations can be resolved if short‐term storage of dissolved gas in upper water layers is considered to influence only the former.
The response of the equatorial ocean to a moving wind field
Authors: McCreary Julian P. , Lukas Roger
Published: February 2008

A linear, viscid, continuously stratified model is used to study the response of the equatorial ocean to forcing by a wind patch moving zonally at the velocity U. For simplicity, solutions are found in an unbounded basin, and transient effects are ignored. This problem is mathematically equivalent to one in which the ocean has a uniform background current −U and the forcing is stationary, and it is possible to interpret solutions from either point of view. An important result is that resonant and near‐resonant Rossby and Kelvin waves can be preferentially excited over other equatorially trapped waves forced by the wind. For two of the solutions, parameters are set as realistically as the model allows, and the solutions are compared with observations. One of them is forced by an eastward moving wind field like the westerly wind anomaly associated with the 1982–1983 El Niño event. It develops subsurface, anomalously westward flow that is strong enough to eliminate the normal Equatorial Undercurrent. The other is forced by a stationary wind in the presence of a weak, westward background current. It has a current structure in the deep ocean that resembles observations of deep equatorial jets, but the surface currents are not realistic. Near‐resonant Kelvin waves contribute significantly to both solutions and are responsible for their interesting properties.
The mass and heat budget in a model of the tropical Atlantic Ocean
Authors: Philander S. G. H. , Pacanowski R. C.
Published: February 2008

In a general circulation model of the tropical Atlantic Ocean, the northwestward flowing Brazilian Coastal Current is fed by the westward South Equatorial Countercurrent and in turn loses water to the eastward Equatorial Undercurrent and the eastward North Equatorial Countercurrent. The transport of the Countercurrent decreases in a downstream direction primarily because of downwelling and then equatorward flow, in the thermocline, into the undercurrent. Some of the Countercurrent water penetrates into the Gulf of Guinea, where it flows into the southern hemisphere. The transport of the Equatorial Undercurrent decreases because upwelling, which is most intense in the western side of the basin, transfers fluid into the surface layers to sustain divergent Ekman drift which is swept westward by the South Equatorial Undercurrent. The model has a northward heat transport across all latitudes in the tropics. Seasonal variations in this transport are modest to the south of 5°S and to the north of 15°N. Across 8°N, however, the transport varies from 1.5 × 1015 W in January and February to −0.1 × 1015 W in August. This result implies that the zonal bands 5°S to 8°N and 8°N to 15°N act as capacitors that are out of phase. In July, August, and September the heat gained from the southern hemisphere is stored in the 5°S to 8°N band where the thermocline deepens. During this period (when the Brazilian Coastal Current turns offshore near 5°N) the thermocline between 8°N and 15°N rises as heat is lost across 15°N. When the Brazilian Coastal Current flows continuously along the coast into the Gulf of Mexico, from December into May, it transports heat from the band 5°S to 8°N to replenish the heat stored between 8°N and 15°N and to sustain the heat flux across 15°N.
Seasonal cycles of currents, temperatures, winds, and sea level over the northeast Pacific continental shelf: 35°N to 48°N
Authors: Strub P. T. , Allen J. S. , Huyer A. , Smith R. L. , Beardsley R. C.
Published: February 2008

Seasonal cycles of coastal wind stress, adjusted sea level (ASL), shelf currents, and water temperatures off the west coast of North America (35°N to 48°N) are estimated by fitting annual and semiannual harmonics to data from 1981–1983. Longer records (9–34 years) of monthly ASL indicate that these two harmonics adequately represent the long‐term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles. We characterize the differences between fall/winter and spring/summer as follows: For fall/winter, monthly mean winds north of 35°N are northward for 3–6 months (longer in the north than in the south); south of 35°N, the mean winds are near zero or weakly southward; monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures. For spring/summer, monthly mean wind stresses are southward at all latitudes for 3–6 months (longer in the south than in the north), sea levels are low, and water temperatures are relatively cool; monthly mean currents at 35 m depth over the shelf are southward for 1–6 months (longer at the shelf break than over midshelf and longer in the north than in the south), while the deeper currents are less southward or northward. The magnitudes of the seasonal cycles of all variables are maximum between approximately 38°N and 43°N, generally decreasing slightly to the north and greatly to the south. At each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1–2 months. The seasonal cycles of all variables show a south‐to‐north progression (south leads north by 1–2 months). At 48°N, annual mean currents at 50 m depth over the shelf break oppose the annual mean wind (northward wind and southward current). Similarly, at 35°N, annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind (southward wind and northward current). From 35°N to 43°N, both summer and winter regimes are dominated by strongly fluctuating currents.
A description of the 1981 and 1982 spring transitions over the Northern California Shelf
Authors: Lentz Steven J.
Published: February 2008

The spring transition between winter and summer conditions on the northern California continental shelf occurred suddenly, over a period of days, in late March in 1981 and in mid‐April in 1982. The spring transition marks the onset of the upwelling season over the continental shelf and is a response to an atmospheric spring transition associated with a sudden seasonal change in the large‐scale atmospheric pressure field over the North Pacific. The 1981 and 1982 spring transitions over the northern California shelf are characterized by a drop in the water temperature over the shelf of 2°–4°C and a reduction of the temperature difference across the water column at midshelf from 2°C to 0.5°C. Isotherms and isopycnals, which were level prior to the spring transition, slope upward toward the coast after the spring transition. The mass balance for the 1982 spring transition event is roughly two dimensional, with offshore flow near the surface balanced by weaker subsurface onshore flow. The alongshore momentum balance during the 1982 spring transition is not two dimensional and includes the establishment of an alongshore pressure gradient which opposes the wind and apparently drives a poleward flow observed during a period of weak wind following the spring transition. The cross‐shelf momentum balance is geostrophic, with density fluctuations contributing to the cross‐shelf pressure gradient. The heat budget for the spring transition event is roughly two dimensional, with the drop in temperature due primarily to a cross‐shelf exchange of heat associated with the cross‐shelf circulation.
A description of subtidal pressure field observations on the Northern California Continental Shelf during the Coastal Ocean Dynamics Experiment
Authors: Brown Wendell S. , Irish James D. , Winant Clinton D.
Published: February 2008

During the Coastal Ocean Dynamics Experiment (CODE) along the northern California continental shelf in the spring and summer of 1981 and 1982, the first comprehensive effort to obtain all of the observations necessary to infer pressure fluctuations throughout the water column was made. This is a description of the subtidal fluctuations in measured bottom pressure, internal pressures inferred from moored conductivity and temperature observations, and the water column total pressure anomalies computed from a combination of the two components. The pressure field during CODE 2 (April‐July 1982) is found to be more energetic than that in CODE 1 (April‐July 1981), with more than 70% total pressure variance concentrated at frequencies of less than (15 days)−1. The spatial structure of the pressure fluctuation field is characterized by coastal intensification and a tendency for poleward phase propagation. Like the pressures, most of the CODE across‐shelf pressure difference variance is found at the lower frequencies, with more than 60% of the total across‐shelf pressure difference variance at frequencies of less than (15 days)−1 The CODE across‐shelf pressure differences are found to be in geostrophic balance with both alongshelf currents and the total alongshelf transport. The alongshelf pressure difference variance is generally found to be concentrated at the lower frequencies much like that of the across‐shelf pressure differences. Most of the pressure and pressure difference variance is found to be highly coherent with wind stress. The 20‐day band pressure variability is apparently related to the response of the pressure field during so‐called “relaxation events.” The barotropic component of the alongshelf geostrophic transport (i.e., across‐shelf pressure difference) has been found to be almost perfectly coherent with regional wind stress τy and to propagate poleward within the CODE region at the same rate as τy and the alongshelf pressure gradient is very important in accelerating the alongshelf flow. The 5‐day band pressure variability in the CODE region appears to result from local wind stress fluctuations. The alongshelf pressure gradient was found to be of secondary importance relative to the wind in accelerating the alongshelf flow.
Structure of the coastal current field off northern California during the Coastal Ocean Dynamics Experiment
Authors: Kosro P. Michael
Published: February 2008

For 74 days during the spring and summer upwelling seasons of 1981 and 1982, in conjunction with the Coastal Ocean Dynamics Experiment, profiles of upper ocean currents were collected in the waters over the shelf and slope off northern California using a shipboard Doppler acoustic log. These measurements provide detailed information on the spatial structure of the current field. Synoptic maps of near‐surface currents often deviate substantially from classical two‐dimensional wind‐driven upwelling and indicate a close association between the complex temperature structures observed in satellite imagery and the presence of vigorous current structures including squirts (regions of intense seaward flow), eddies, and countercurrents. Well‐defined examples of a squirt and of a countercurrent during a cessation of wind forcing (wind relaxation event) are examined in detail. Despite this complexity, the nearshore synoptic current field was found to be anisotropic, varying more rapidly cross shore than alongshore. The structure of the current averages and simple fluctuation statistics were largely as deduced in other upwelling areas from moored measurements. A surface‐intensified equatorward jet was found in the average alongshore currents, with vertical shear exceeding −2 × 10−3 s−1 over much of the shelf. The core of the jet moved offshore south of Point Arena and was better resolved in along‐isobath averages. At depths below 80 m the average alongshore flow reversed, giving way to a poleward undercurrent, strongest near the shelf break. The detailed structure of the inferred cross‐shore circulation was found to be sensitive to the coordinate system selected. Using nominal (along‐coast) coordinates, the average cross‐shore current was found to be directed offshore within a surface layer which deepened with distance from the coast out to the shelf break, showed strong vertical shear only near the surface, and was divergent in the upper water column and convergent in the lower water column over the shelf. Current fluctuations about the local mean were strongly polarized along isobaths near the coast and became largely isotropic far from shore except offshore from Point Arena, where squirts were recurrently observed.
In situ wind measurements and the ocean response in the equatorial Atlantic during the Programme Francais Ocean et Climat Dans l'Atlantique Equatorial and Seasonal Response of the Atlantic Ocean Experiment
Authors: Colin Christian , Garzoli Silvia L.
Published: February 2008

In situ wind measurements collected as part of the Programme Français Océan et Climat dans l'Atlantique Equatorial (FOCAL)/Seasonal Response of the Equatorial Atlantic (SEQUAL) experiment (1983–1984) in the western and eastern parts of the equatorial Atlantic basin are described. They were obtained from meteorological stations placed Saint Peter Peter and Saint Paul Rocks (SPP) (1°N, 29°W) and at the top of a surface buoy moored in the Gulf of Guinea (0°N, 4°W). From the wind observations the wind stress was inferred, and results are compared with climatology. The wind stress time series show the abrupt increase of the winds during the spring that, at SPP, reaches a value as high as 0.35 dyn/cm2 in 2 weeks for both observed years. The 11‐day running mean time series shows that the onset of the zonal component of the wind stress occurs at SPP on April 10, 1983, and on May 17, 1984, and in the Gulf of Guinea (GG) on April 5, 1983, and April 10, 1984. The monthly mean observations show an interannual variability both in the time of the onset and in the strength of the trade winds. At SPP and GG the total wind stress increases 1 month earlier than climatology in 1983 but at the same time as climatology in 1984. At SPP the zonal component of the wind stress also intensifies 1 month earlier than climatology in 1983 but 1 month later in 1984. The equatorial temperature records at 28°W and 4°W show that the depth of the 20°C isotherm, on a seasonal time scale, decreases during the relaxation period of the trade winds (boreal winter). In 1983–1984 this occurred in December 1983 at 28°W and in March 1984 at 4°W. After the onset of the local trade winds, the thermocline continues to move upward during 1 month at 28°W and during 3 months at 4°W; thereafter, the thermocline deepens at both locations. At the surface, the temperature decreases when the trade winds intensify and remains low as long as the trade winds are blowing. The seasonal variations of the temperature both at the surface and below the surface at 28°W and 4°W are interpreted in the light of the results of a nonlinear multilevel model in the cases of a sudden increase and a sudden relaxation of the trade winds.
Response of the equatorial Atlantic Ocean to the 1983–1984 wind from the Programme Français Océan et Climat Dans l'Atlantique equatorial cruise data set
Authors: Hisard Philippe , Hénin Christian
Published: February 2008

Variations of the zonal pressure gradient (ZPG) and the Equatorial Undercurrent (EUC) are described in the equatorial Atlantic Ocean (between 34° 30′W and 6°30′E) as observed during eight pairs of Programme Français Océan et Climate dans l'Atlantique Equatorial cruises between October 1982 and August 1984. In 1982 and 1983 the annual cycle of weak trades early in the year, followed by comparatively strong and sustained trades, were relatively normal. In the boreal winter of 1984, the extent of the collapse of the trade winds was exceptional, and consequences were observed in the upper layers of the ocean along the equator. The 20°C isotherm depth, representative of the thermocline depth, was unusually deep along the equator in the Gulf of Guinea. A near‐zero value of the ZPG was observed from the Greenwich meridian westward. An eastward surface current, separated from the EUC by a layer of reduced velocity, was observed over much the same fetch. West of 10°W the maximum velocity of the EUC showed very little seasonal variation, usually between 70 and 80 cm s−1, except in the boreal fall of 1983 when it exceeded 100 cm s−1. During this period (in both 1983 and 1984) the EUC transport at 23°W reached 25 × 106 m3 s−1, or twice its annual average, which derived not only from the increase in speed but also for a deepening of the current to below 100 m. It was also the season when the ZPG was strongest and has a similar amplitude at both the surface and 50 dbar relative to 500 dbar. The seasonal variations of the EUC in the Gulf of Guinea were even more pronounced. During the boreal summer and fall, the current weakened, while the local ZPG reversed direction compared to the west. The stronger penetration of the EUC into the gulf occurred in the alternate seasons when there was no local reversal in the eastward acting ZPG force. The large changes in the oceanic and atmospheric circulation during the 1983–1984 period are hypothesized to be related to the suppression of the coastal period are hypothesized to be related to the suppression of the coastal Benguela upwelling along the Namibia coast. This Atlantic equivalent to El Niño occurred 1 year after the exceptionally strong event in the Pacific.
Coastal atmospheric forcing in the northern Gulf of Alaska
Authors: Luick John L. , Royer Thomas C. , Johnson Walter R.
Published: February 2008

A comparison of winds over the northern Gulf of Alaska found measured winds to be significantly weaker than calculated geostrophic winds. The latter required more than the standard 30% reduction to correct for frictional effects in the maritime boundary layer. An additional 11% is calculated based on principal axis analysis. A counterclockwise rotation of the instantaneous geostrophic wind vectors of 44° (59° total) beyond the standard 15° was required to align them with those measured at a coastal weather station. However, events in these two wind sets were well correlated throughout the year, and the rotary coherence was significant for frequencies lower than 0.895 cpd. On the basis of empirical orthogonal function analysis, most of the seasonal variability in this coastal current is associated with wind changes. Freshwater discharge is also important in driving the alongshore baroclinic flow and a secondary cross‐shelf flow.
Analysis of horizontally two‐dimensional morphological evolutions in shallow water
Authors: De Vriend H. J.
Published: February 2008

A system of depth‐integrated equations, forming a rather primitive mathematical model of horizontally two‐dimensional (2DH) bed evolutions in shallow water, is analyzed using characteristics theory. The analysis shows that the solution of this system exhibits an essentially two‐dimensional propagation character, with bottom disturbances traveling in other directions than the current velocity and the sediment transport. The results of this analysis are verified by numerical experiments and interpreted physically. Their relevance for numerical modeling of 2DH morphological processes in shallow water is discussed, and their occurrence and recognizability in natural situations is checked by a qualitative comparison with field observations.
Wave refraction by a current whirl
Authors: Mathiesen Martin
Published: February 2008

A computer model for the computation of refraction of ocean directional wave spectra has been developed. The model is applied to wave propagation through a circular current whirl. Both refraction diagrams and computed directional wave spectra are presented. Wave heights are computed for points outside the whirl. Relative changes in wave heights are found to be within ±20%. The computations reveal two areas of crossing seas on the lee side of the whirl. Between these areas is an area of reduced wave heights and nearly unidirectional waves.
Global surface wind and flux fields from model assimilation of Seasat data
Authors: Atlas R. , Busalacchi A. J. , Ghil M. , Bloom S. , Kalnay E.
Published: February 2008

The entire 96‐day period of Seasat scatterometer data has been objectively dealiased using the Goddard Laboratory for Atmospheres (GLA) analysis/forecast system, and global fields of wind stress and sensible and latent heat fluxes were produced as a by‐product of the data assimilation process. The GLA objectively dealiased winds were compared with a more limited subjectively dealiased data set and with objectively dealiased winds obtained using an alternative method. Good general agreement between the three methods was found. The GLA objective method was also verified using simulated Seasat data. Monthly mean analyses of wind stress and latent heat flux agreed well with climatological fields and known atmospheric and oceanic features. Monthly mean sensible heat flux fields differed substantially from climatology, but in a limited number of subjective comparisons with observed atmospheric features the instantaneous fields were found to be reasonable.
Current regimes across the East Greenland Polar Front at 78°40′ north latitude during summer 1984
Authors: Manley T. O. , Hunkins K. L. , Muench R. D.
Published: February 2008

Four weeks of concurrent temperature and current observations from three moorings across the East Greenland Polar Front, at approximately 78°40′N, showed pronounced differences between the current regimes on either side of the front. East of the front, vertical shear was minimal, mean flow was not statistically significant, and fluctuations showed evidence of wind influence. West of the front, vertical shear and southward mean flow were significant; however, observed fluctuations were not strongly influenced by local winds. The mean current and density structure of the front was similar to that of a two‐layer boundary current model with constant potential vorticity. Current fluctuations west of the front were in part related to mesoscale features generated farther north and subsequently advected downstream by the East Greenland Current or to eddylike features apparently generated through potential vorticity conservation. Local instabilities of the front most likely account for the remainder of the mesoscale variability seen in the records.
Tomographic resolution of mesoscale eddies in the marginal ice zone: A preliminary study
Authors: Chiu Ching‐Sang , Lynch James F. , Johannessen Ola M.
Published: February 2008

The adequacy of ocean acoustic tomography to resolve mesoscale eddies in the marginal ice zones (MIZ) in the vertical plane containing the acoustic multipaths connecting a pair of transceivers is studied using simulation inversions based on realistic eddy profiles obtained from conductivity‐temperature‐depth data. Resolution in this plane is seen to be strongly dependent upon the characteristics of the sound channel. For optimal, minimum mean square error estimators, resolution is directly related to accuracy, with better resolution implying higher accuracy. For unaided acoustic tomography (i.e., no supplementary measurements) using only non‐bottom‐interacting paths, horizontal and vertical resolution lengths of the order of 40 km and 200 m, respectively, are found in the upper water column for a transmission range of 150 km. The implication is that the horizontal resolution is marginally adequate to resolve MIZ eddies but the vertical resolution is not, since the horizontal scale of the eddies is of the same order whereas the vertical scale is much shorter. The incorporation of bottom‐reflected arrivals is found to improve resolution significantly. However, the improvement only occurs in the horizontal direction and saturates when more than 14 of these arrivals are included. Beyond this point, additional travel time observations give mostly redundant information. On the other hand, the disappearance of less stable non‐bottom‐interacting ray paths can result in a significant loss of resolution, but only vertically. The deficiency in vertical resolution is a result of the upward refracting nature of the MIZ sound channel. It is also demonstrated that the inclusion of point temperature measurements on the acoustic transceiver moorings can dramatically increase the vertical resolution of the overall system, particularly within a horizontal correlation length of the mooring. With the inclusion of satellite radiometry surface temperature measurements, adequate vertical resolution is achieved over the entire range considered.
Fine structure, internal waves, and intrusions in the marginal ice zone of the Greenland Sea
Authors: Foster Theodore D. , Eckert Eric G.
Published: February 2008

Two series of 40 temperature and salinity profiles were made in the marginal ice zone of the northeastern Greenland Sea/Fram Strait region. The first series showed much intrusive activity, while the second was dominated by internal wave activity. Displacement dropped spectra showed spectral levels scaled by Desaubies' (1976) analytic representation of the Garrett‐Munk (1975) model to be comparable to those from lower latitudes though probably somewhat lower. Temperature dropped spectra showed severe contamination by intrusions. It is concluded that temperature spectra cannot be used to determine internal wave activity of the upper ocean in the marginal ice zone.
Boundary layer, upper ocean, and ice observations in the Greenland Sea Marginal Ice Zone
Authors: Morison James H. , McPhee Miles G. , Maykut Gary A.
Published: February 2008

During the 1984 Marginal Ice Zone Experiment, a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone (MIZ) of the Greenland Sea. The measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence, profiles of water temperature, salinity, and velocity, ice ablation, ice concentration, solar radiation, and spectral albedos. Ocean conditions were found to be extremely variable. The ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s−1. In the course of the drift, a 30‐km eddy was crossed wherein ice and water velocities exceeded 15 cm s−1. The northern extension of the East Greenland Polar Front was encountered, and a northward flow of Atlantic Water into the Arctic basin was observed below the eastern edge of the front, but the drift station never moved quite far enough west to be caught in the southward transport of Arctic Surface Water. Heat from the ocean was a major factor in ice melt, and when the ice was over Atlantic Water it was the dominant factor. The events that had the greatest impact on the ice were two “outbreaks” during which off‐ice winds blew the ice across warm ice edge ocean fronts. Once south of these fronts and over surface water as warm as 1°C, the ice bottom melted at rates up to 100 kg m−2d−1. The rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients. The drag coefficient (relative to the square of the relative water velocity at 30 m) ranged from 0.002 to 0.02 and averaged 0.006. The heat transfer coefficient (relative to the friction velocityu*and the mixed layer temperature elevation above freezing) ranged from 0.0025 to 0.009 and averaged 0.0038. In agreement with the idea that stratification inhibits turbulent exchange, the heat transfer coefficient decreased when stratification increased. In fact, the observed melt rates can be simulated well if molecular heat and salt transfer through a thin, near‐surface, laminar boundary layer are accounted for, as well as transfer through the turbulent outer boundary layer. Also in agreement with turbulent boundary layer theory, the drag coefficient decreased when stratification increased slightly above neutral. However, for the large increases in surface stratification, the drag coefficient increased. This was due to the generation of internal gravity waves by ice bottom roughness. Because the surface exchange coefficients are so sensitive to surface stratification, which is in turn highly variable in the MIZ, accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice‐ocean interactions and upper ocean conditions.
Beaufort‐Chukchi ice margin data from Seasat: Ice motion
Authors: Carsey Frank , Holt Benjamin
Published: February 2008

The motion of sea ice in the summer and fall marginal zone of the Beaufort and Chukchi seas is observed by tracking ice features in sequential Seasat synthetic aperture radar images. Four examples of ice motion fields are shown and discussed with translation observation density finer than one observation per 5 km for the most part. In this region the components of proportional relative motion are shown to commonly have values in the range 0.1 to 0.25/day throughout the marginal zone, which itself has a scale of the order of 100 km.