bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass and heat budgets on the northern California continental shelf
Authors: Rudnick Daniel L. , Davis Russ E.
Published: February 2008

The mass and heat budgets on the northern California continental shelf between Point Arena and Point Reyes are examined using moored measurements of horizontal water velocity and temperature made during the second Coastal Ocean Dynamics Experiment (CODE 2). Empirical orthogonal functions (EOFs) are employed to identify components of current and temperature variability with scales that are resolved by the observations. A constrained least squares fit to the EOF‐filtered data is used to find maps of velocity which conserve mass and maps of temperature which conserve heat integrated over control volumes. The wind during CODE 2 is characterized by strong southward “events” separated by “relaxations” of the wind. Currents are southward and offshore during events and northward and only slightly onshore during relaxations. Vertical velocity is estimated from the divergence of the massconserving horizontal velocity field. Upwelling occurs during wind events, with the strongest upwelling occurring nearshore and just to the south of Point Arena. Downwelling is observed during each relaxation but is too weak to be statistically significant. Water temperature rises gradually during relaxations and drops quickly near the beginning of events. The vertical turbulent heat flux at a depth z is estimated as the residual in the heat budget of a volume bounded by the surface and z after accounting for heat advection and surface heat flux. Statistically significant mixing is found at the beginning of two events and is followed by strong advective cooling. Close to shore, heat is advected primarily in the cross‐shore direction, while farther offshore, alongshore advection is also important. The pattern of vertical mixing followed by offshore advection, as observed near shore, is that predicted by two‐dimensional models of upwelling which include mixed‐layer dynamics.
The westward turning branch of the West Spitsbergen Current
Authors: Bourke R. H. , Weigel A. M. , Paquette R. G.
Published: February 2008

A salinity‐temperature survey of Fram Strait in September 1985 extending to north of 81°N demonstrated the western branch of the West Spitsbergen Current flowing northwest and then west, mainly south of 81°N. There also was a southwestward recirculation from the eastern branch of the West Spitsbergen Current. Baroclinic flow of warm water northward through 81°N was negligible or zero. Some doubt is cast on past flow diagrams based on core analysis which show the western branch of the West Spitsbergen Current coursing northward to 83°N. One of a probable line of mesoscale eddies is described in some detail.
Skin friction probes for field applications
Authors: Gust Giselher
Published: February 2008

A technique has been developed which measures skin friction in marine, limnological, and flume boundary layers, with and without suspended particulate matter, by constant temperature anemometry. With sensor scales of ∼3 mm and frequency responses ≧20 Hz, flush‐mounted, epoxy‐coated hot films yield mean and fluctuating components of wall shearing stress at water depths ≦7000 m. Calibration and deployment techniques show that the probes can measure the magnitude of skin friction τ up to 2 N m−2 with sensitivities ≧0.1 V/0.1 N m−2 and accuracies of ±10% (20%) for mean (fluctuating) wall shearing stresses ≧0.016 N m−2 at the 95% uncertainty level. Two‐dimensional versions of the probes measure magnitude and direction of τ as well as the longitudinal vorticity ωx. Measurement errors of the skin friction probes are 2 to 6 times smaller than uncertainty levels for wall shearing stresses calculated by the logarithmic layer technique from velocity profiles under the same flow conditions, topography permitting. The seagoing skin friction sensors yield data without special requirements on shape or steadiness of the mean vertical flow profile, resolve turbulent wave boundary layers, and measure skin friction in sediment‐laden flows as long as (partial) viscous sublayers are present.
Upwelling off the Gulfs of Panama and Papagayo in the tropical Pacific during March 1985
Authors: Legeckis Richard
Published: February 2008

Satellite measurements of sea surface temperatures (SST) were made in the eastern tropical Pacific Ocean during March 1985. Unusually persistent upwelling was observed southwest of the Gulf of Panama and Gulf of Papagayo from March 7 to 22. The SST was depressed by 6° to 10°C relative to the surrounding waters. The cooler waters off Panama extended southwestward for over 1000 km and reached the Galapagos Islands. The northern SST front off Panama was wavelike in appearance, and long waves of 600‐km length moved southwestward at a phase speed of about 30 km/d. These waves resemble the long waves that appear each year along the northern boundaries of the equatorial SST fronts in the Pacific and the Atlantic oceans. The SST fronts off the Gulf of Papagayo remained relatively stationary, with a large area of colder water centered at 88°W and 10°N. During these events, the upwelling off the Gulf of Tehuantepec was relatively weak. These satellite observations provide a view of an unusual oceanic response on the leeward side of mountain pass wind jets.
An oceanographic flip‐flop: deep water exchange in Fortune Bay, Newfoundland
Authors: Hay Alex E. , de Young Brad
Published: February 2008

Observations are presented of deep‐water exchange in a large coastal embayment on the south coast of Newfoundland. The bay has several outer sills not unlike those found in fjords. Outside the bay, two submerged channels on the continental shelf are reservoirs for two different deep‐water masses which may flow over separate sills to replace deep water within the bay. The deep water is renewed approximately twice a year. On average, exchange occurs both during the half‐year period centered on midwinter and during the half‐year period centered on late summer, with the water properties of the inflow in each period being dominated by one of the two source water masses in the shelf channels. The system therefore occupies one of two renewal states for much of the year. The transition between states appears to be induced largely by seasonal variations in the wind forcing over the shelf.
The 26‐ and 50‐day oscillations in the western Indian Ocean: Model results
Authors: Kindle John C. , Thompson J. Dana
Published: February 2008

The circulation of the western Indian Ocean is examined using a reduced‐gravity model with one active layer and realistic basin geometry for the entire Indian Ocean north of 30°S. The Hellerman and Rosenstein monthly mean wind stress climatology is used to force the model. The numerical simulations reproduce the observed (Luyten and Roemmich, 1982) 26‐day waves along the equator and the 50‐day oscillations (Mysak and Mertz, 1984; Schott et al. 1988) between the equator and Madagascar. The 25‐ to 28‐day oscillations of the model meridional velocity component agree with observed values of period, amplitude, wavelength, group velocity, and phase of the seasonal modulation. The model oscillations, which are excited in August and persist into February–March, are shown to be the result of Yanai waves generated between the western boundary and 50°E. During the southwest monsoon, the Yanai waves are initiated by a complex barotropic instability associated with the southern gyre. During the early stages of the northeast monsoon, the 26‐day Yanai waves are generated by resonant forcing due to the intrusion into the equatorial waveguide of a standing, 800‐ to 900‐km‐wavelength meander of the eastward flow fed by the East African Coastal Current. Hence the simulation reveals that the 26‐day oscillations in the equatorial Indian Ocean are excited by mechanisms significantly different than that believed to be responsible for the 20‐ to 30‐day oscillations in the equatorial Atlantic and Pacific oceans. The numerical simulation also shows a 50‐day oscillation between the equator and Madagascar west of 50°E. This periodicity is due to Rossby waves generated by a barotropic instability associated with the East African Coastal Current beginning about April each year. No evidence of the 50‐day period oscillation is found in a corresponding linear simulation. Hence the barotropic instability of the oceanic currents in this region is offered as an alternative to direct wind forcing as the generating mechanism for the observed 40‐ to 60‐day oscillations in the western Indian Ocean.
Observed and modeled annual cycle of transport in the Straits of Florida and east of Abaco Island, the Bahamas (26.5°N)
Authors: Rosenfeld Leslie K. , Molinari Robert L. , Leaman Kevin D.
Published: February 2008

Direct velocity observations were collected with a free‐fall acoustic velocity profiler along an east‐west section extending 65 km offshore of Abaco Island, the Bahamas (26.5°N). The section, which includes five stations, was occupied 14 times between September 1984 and September 1987. The two inshore stations were located on the continental slope, and the three offshore stations were located over the abyssal plain (at depths approaching 4700 m). The average total section transport between the surface and 2500 m (the portion of the water column best sampled) was 10 Sv (1 Sv = 106 m3/s) to the south. The range of transports is 40 Sv with maximum northward transport observed during April 1985 (5.3 Sv) and maximum southward transport observed during April 1986 (34.8 Sv). The average flow above 800–900 m is to the north at the four westernmost stations and is to the south below 800–900 m and over most of the easternmost station. The southward flow includes the Deep Western Boundary Current. Strong vertical shears extend to 1100 m. An approximation for the upper layer (above 1100 m) baroclinic transport has a mean of 12.2 Sv to the north and a range of 15 Sv. Results from a two‐layer and a one‐and‐a‐half‐layer wind‐driven model are compared with the annual cycles of total and upper layer transport, as determined from the observations. The barotropic transport from the two‐layer model has a range of the order of ±10 Sv, with a winter maximum and fall minimum. The range of the baroclinic transport from the one‐and‐a‐half‐layer model is an order of magnitude smaller and of opposite sign. Although there are similarities between the observations and the results of both models, the small signal‐to‐noise ratio precludes definitive confirmation of the annual cycle. The situation east of the Bahamas, where the two models give very different predictions, is compared with the Straits of Florida, where both models predict an annual cycle similar to that observed for the total transport. The roles played by topography and local and remote wind forcing in producing these results are discussed.
A numerical model of the atmospheric boundary layer over a marginal ice zone
Authors: Kantha Lakshmi H. , Mellor George L.
Published: February 2008

A two‐dimensional, multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off‐ice, on‐ice, and along‐ice edge wind conditions. The model incorporates a second‐moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects. For off‐ice winds, as the atmospheric boundary layer passes from cold smooth ice onto warm open water, the onset of intense convection raises the inversion. Over the transition zone of rough rafted ice with open leads, the shear stress on the ice cover increases significantly before dropping down to the downstream values over water. Such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone. These results are in agreement with the one‐layer model simulations of off‐ice winds by Overland et al. (1983). For on‐ice wind conditions, as the warm flow in the boundary layer encounters the cold ice conditions, the resulting stable stratification could rapidly suppress the turbulence in the boundary layer, leading to the development of a shallow inversion and an associated jet. When the wind is predominantly along the ice edge, the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence. More observations are needed to verify these model predictions. Nevertheless, these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions.
A double vortex along the California coast
Authors: Sheres David , Kenyon Kern E.
Published: February 2008

A double vortex was observed at the entrance to the Santa Barbara Channel, California, with sequential IR imagery from the NOAA 7 satellite during May 1984. While the wind blew strongly to the southeast, the double vortex moved westward with a velocity greater than that estimated for the mutual interaction of two idealized vortices. The effect of the double vortex on incoming Pacific swell is calculated by numerical integration of the ray equations. This calculation shows areas of focusing of the rays near the entrance to the channel, which suggests elevated wave energy there with reduced wave energy nearby. The pattern of wave refraction by mesoscale features, such as a double vortex, can help detect them and estimate their velocity distribution from remotely sensed surface wave imagery. The similarities and differences between refraction patterns produced by double vortices and by eddies is outlined. The double vortex and its generation by an episodic or tidal flow is investigated using Kashiwai's (1984) approach. An example of the related generation of a single vortex in the Alboran Sea by tidal flow in the Strait of Gibraltar is briefly discussed.
Worldwide ship drift distributions identify missing data
Authors: Richardson P. L.
Published: February 2008

The geographical and temporal distributions of worldwide ship drift velocities were plotted in order to see where and when the observations were made and to identify what appear to be major gaps in the data. Curiously, large areas of the North Atlantic, North Pacific, and South Pacific were found to be devoid of observations in some months during the years 1920–1934 when the number of yearly observations is large. An estimated 700,000 observations are missing. These would significantly enhance the usefulness of the data set if they could be found and added to it, especially in the Pacific where the data density is low.
Simulations of radiocarbon in a coarse‐resolution world ocean model: 1. Steady state prebomb distributions
Authors: Toggweiler J. R. , Dixon K. , Bryan K.
Published: February 2008

This paper presents the results of five numerical simulations of the radiocarbon distribution in the ocean using the Geophysical Fluid Dynamics Laboratory primitive equation world ocean general circulation model. The model has a 4.5° latitude by 3.75° longitude grid, 12 vertical levels, and realistic continental boundaries and bottom topography. The model is forced at the surface by observed, annually averaged temperatures, salinities, and wind stresses. There are no chemical transformations or transport of 14C by biological processes in the model. Each simulation in this paper has been run out the equivalent of several thousand years to simulate the natural, steady state distribution of 14C in the ocean. In a companion paper the final state of these simulations is used as the starting point for simulations of the ocean's transient uptake of bomb‐produced 14C. The model reproduces the mid‐depth 14C minimum observed in the North Pacific and the strong front near 45°S between old, deep Pacific waters and younger circumpolar waters. In the Atlantic, the model's deep 14C distribution is much too strongly layered with relatively old water from the Antarctic penetrating into the northern reaches of the North Atlantic basin. Two thirds of the decay of 14C between 35°S and 35°N is balanced by local 14C input from the atmosphere and downward transport by vertical mixing (both diffusion and advective stirring). Only one third is balanced by transport of 14C from high latitudes. A moderately small mixing coefficient of 0.3 cm2 s−1 adequately parameterizes vertical diffusion in the upper kilometer. Spatial variation in gas exchange rates is found to have a negligible effect on deepwater radiocarbon values. Ventilation of the circumpolar region is organized in the model as a deep overturning cell which penetrates as much as 3500 m below the surface. While allowing the circumpolar deep water to be relatively well ventilated, the overturning cell restricts the ventilation of the deep Pacific and Indian basins to the north. This study utilizes three different realizations of the ocean circulation. One is generated by a purely prognostic model, in which only surface temperatures and salinities are restored to observed values. Two are generated by a semidiagnostic model, in which interior temperatures and salinities are restored toward observed values with a 1/50 year−1 time constant. The prognostic version is found to produce a clearly superior deep circulation in spite of producing interior temperatures and salinities which deviate very noticeably from observed values. The weak restoring terms in the diagnostic model suppress convection and other vertical motions, causing major disruptions in the diagnostic model's deep sea ventilation.
Secondary circulations in the bottom boundary layer over sedimentary furrows
Authors: Viekman Bruce E. , Wimbush Mark , Van Leer John C.
Published: February 2008

Secondary circulation is known to be an important feature of many atmospheric and laboratory boundary layers. The presence of streamwise, helical, counterrotating vortices is documented here for the first time in the bottom boundary layer of a large natural body of water. Simultaneous vertical profiles of velocity and temperature were recorded on either side of a sedimentary furrow on the floor of Lake Superior (depth = 100 m) in November 1985. Flow roughness length zo was estimated to be 0.3 cm. Friction velocity u* and turbulent boundary layer thickness LW were estimated for each profile allowing for stratification effects. Typically, LW ≈ 10 m. Thermal stratification near the lake bed was an important constraint to boundary layer development; bottom mixed layers were absent in most cases. Mean flow toward the furrow at lower levels within the boundary layer (z/LW<0.37) and mean flow away from the furrow at higher levels (0.37 < z/LW < 1.65) were observed for near‐bottom speeds greater than 6 cm/s when mean flow direction was within 25° of the furrow direction. This implies helical vortex pair circulations with upward motion over the furrow, consistent with earlier hypotheses. Cross‐stream (secondary) flows were typically 5% of the free stream (primary flow) speed. Streamwise vorticity in the range 1.5 m ≤ z ≤ 5 m was estimated to be 2.1×10−3 s−1.
Sea surface velocities in shallow seas extracted from sequential coastal zone color scanner satellite data
Authors: Garcia Carlos A. E. , Robinson Ian S.
Published: February 2008

Sequential images of visible wavelength reflectance from channel 3 (540–560 nm) of the Coastal Zone Color Scanner (CZCS) have been used for computing advective velocities in the eastern English Channel, using the maximum cross‐correlation technique. The computation method, known as matched filtering, is widely used by meteorologists and has recently been applied by oceanographers to detect sea surface motion from satellite infrared images. Provided accurate coregistration of images is achieved by matching ground control points, significant correlation is obtained when the technique is applied to CZCS data, and coherent velocity distributions are obtained for United Kingdom shelf waters. The residual circulation patterns for the English Channel are found to be consistent with previous studies and recent observations.
Instrumentation for estuarine research
Authors: Sternberg R. W.
Published: February 2008

Estuaries are large bodies of water within which interactions of physical, chemical, and biological processes with suspended and bottom sediments are complex. The goals of estuarine sediment transport research are broad and place diverse requirements on instruments and methods of observation. Processes of sediment advection often are investigated with methods that provide synoptic observations over expanded geographical regions, i.e., remote sensing and rapid shipboard reconnaissance techniques. In contrast, time series data collected within an estuary by anchored ships or by moored or semipermanently emplaced instruments are used for the study of the processes or mechanics of sediment resuspension and deposition. Understanding the mechanics of estuarine sediment transport also provides important insights into the regional or advective processes active in estuaries. This paper reviews the present status of methods used for sediment transport research in estuaries. It explores some fundamental sediment transport equations to define measurement requirements, describes various classes of instruments to meet the measurement requirements, and presents examples of individual instruments that have been combined into operational measurement systems. Some potentially important methods under development are also discussed.
Composition and modification of water masses in the Mackenzie shelf estuary
Authors: Macdonald R. W. , Carmack E. C. , McLaughlin F. A. , Iseki K. , Macdonald D. M. , O'Brien M. C.
Published: February 2008

The distributions of δ18O, salinity, temperature, and nutrients have been used to quantify water sources to the Mackenzie shelf in the Beaufort Sea. Comparison of water mass analyses with satellite imagery confirms that the meteoric (runoff) water is associated with the Mackenzie plume. The seasonally variable surface layer for the shelf is viewed as cycling between a “reverse estuary” in winter, when the polar mixed layer (PML) is formed, and a positive estuary in summer when the shelf waters respond to freshwater inputs (runoff and ice melt). We infer a standing stock of 3.7 m fresh water at the end of summer 1986, of which 30% owes its origin to the melting of sea ice; our data coupled with river flow imply a freshwater flushing time for the Mackenzie shelf at about 150 days. To re‐form the PML during winter requires the removal of this seasonal fresh water through the combined processes of flushing and ice formation: once this fresh water has been removed, continued ice growth can produce “new” brine which would be observed as a deeper and saltier PML from the previous year. A simple geochemical model shows that autumn conditions (freshwater accumulation) and the rate of flushing are important controls on the potential of the shelf to produce “new” brine and that winter runoff, were it to distribute evenly across the shelf, is sufficient to inhibit brine production.
Simultaneous temperature and velocity measurements of the internal wave field in the Corsican Channel (eastern Ligurian Sea)
Authors: Artale V. , Gasparini G. P.
Published: February 2008

During a study of circulation in the eastern Ligurian Sea, current and temperature were measured close to the sill of the Corsican Channel between Corsica and the Italian mainland in March–April 1987. Internal wave activity at the interface between the Modified Atlantic Water and the Levantine Intermediate Water was observed. The statistical description of the internal wave field shows some deviations from Garret‐Munk theory. The fine structure has a remarkable influence on the vertical and horizontal scales, which have values smaller than those of theoretical prediction. The mean velocity, together with the topographic constriction, causes significant anisotropy of the internal wave field. The polarization effect is predominantly along channel, while near‐bottom energy intensifications were not observed.
Validation of the geostrophic method for estimating zonal currents at the equator from Geosat altimeter data
Authors: Picaut Joël , Busalacchi Antonio J. , McPhaden Michael J. , Camusat Bruno
Published: February 2008

The applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meridionally differenced form of the geostrophic balance. Estimates of geostrophic zonal flow anomalies in the equatorial Pacific have been deduced from 17‐day collinear altimeter data during the first year of the Geosat Exact Repeat Mission, November 1986 to November 1987. Altimeter‐derived geostrophic estimates agree well with in situ zonal current variability. Comparison of low‐frequency, near‐surface zonal current observed from equatorial moorings at 165°E;, 140°W, and 110°W yield correlations of 0.83, 0.85, and 0.51, respectively, with a mean rms difference of 23 cm s−1. The geostrophic currents were calculated from all available ascending and descending Geosat tracks within ±4.5° of longitude from each mooring site. The inclusion of up to 11 ascending and descending Geosat tracks within the 9° band for every 17‐day repeat effectively reduced the temporal sampling interval to 1.5 days at 165°E and 140°W. However, only ascending tracks were available at 110°W. Alongtrack sea surface heights were first smoothed using a combination of linear and nonlinear filters. The 6.8 km alongtrack spacing of the altimeter measurements provides sufficient resolution for the effective filtering of small‐scale meridional noise, both instrumental and oceanic. High‐frequency temporal variability, such as noise and ageostrophic motions, was suppressed with a 31‐day Hanning filter. Sea level and zonal velocity solutions from a tropical Pacific numerical model were used as proxy data sets in order to estimate errors induced into the geostrophic calculation by the Geosat space‐time sampling.
Oxygen 18 and helium as tracers of ice shelf water and water/ice interaction in the Weddell Sea
Authors: Schlosser Peter , Bayer Reinhold , Foldvik Arne , Gammelsrød Tor , Rohardt Gerd , Münnich Karl Otto
Published: February 2008

Oxygen 18 and helium isotope data from stations located in the Filchner Depression, on the continental slope of the southern Weddell Sea, and in the central Weddell Sea are presented and discussed. The 18O and 4He signals imprinted on the water circulating under the Filchner/Ronne Ice Shelf (Ice Shelf Water, or ISW) due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the Filchner Depression from the Weddell Sea. Low δ18O values are correlated with high 4He concentrations in the ISW found in the Filchner Depression (minimum δ18O values: −0.8‰; maximum 4He concentrations: about 4.7×10−8 cm3 STP g−1). The fraction of glacial meltwater contained in the ISW found in the Filchner Depression is estimated to about 6 to 7‰. The 18O and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that ISW contributes significantly to the Weddell Sea Bottom Water (WSBW). On the basis of a inultiparameter water mass analysis it is discussed which fraction of the WSBW originates from ISW and which other shelf waters potentially could contribute to WSBW.
Sources of variability in satellite‐derived estimates of phytoplankton production in the eastern tropical Pacific
Authors: Banse Karl , Yong Marina
Published: February 2008

As a proxy for satellite (coastal zone color scanner) observations and concurrent measurements of primary production rates, data from 138 stations occupied seasonally during 1967–1968 in the offshore, eastern tropical Pacific were analyzed in terms of six temporal groups and four current regimes. In multiple linear regressions on column production Pt, we found that simulated satellite pigment is generally weakly correlated, but sometimes not correlated with Pt, and that incident irradiance, sea surface temperature, nitrate, transparency, and depths of mixed layer or nitracline assume little or no importance. After a proxy for the light‐saturated chlorophyll‐specific photosynthetic rate pmax is added, the coefficient of determination (r2) ranges from 0.55 to 0.91 (median of 0.85) for the 10 cases. In stepwise multiple linear regressions the pmax proxy is the best predictor for Pt. Pt can be calculated fairly accurately (on the average, within 10–20%) from satellite pigment, the 10% light depth, and station values (but not from regional or seasonal means) of the pmax proxy; for individual stations the precision is 35–84% (median of 57% for the 10 groupings; p = 0.05) of the means of observed values. At present, pmax cannot be estimated from space; in the data set it is not even highly correlated with irradiance, temperature, and nitrate at depth of occurrence. Therefore extant models for calculating Pt in this tropical ocean have inherent limits of accuracy as well as of precision owing to ignorance about a physiological parameter.
A comparison of ship and coastal zone color scanner mapped distribution of phytoplankton in the southeastern Bering Sea
Authors: Müller‐Karger F. E. , McClain C. R. , Sambrotto R. N. , Ray G. C.
Published: February 2008

We examined 21 Coastal Zone Color Scanner (CZCS) images of the southeastern Bering Sea to map the near‐surface distribution of phytoplankton during 1979 and 1980 and compared this information with the mesoscale (100–1000 km) distribution of phytoplankton inferred from ship sampling. Pigment patches coherent over length scales of about 1000 km along isobaths were detected in the satellite data. The patches straddled boundaries of hydrographic domains that were previously defined from the ship observations. Smaller patches (order of 100 km diameter and less) were common. The imagery indicated that open‐water phytoplankton blooms occur first in late April in coastal waters, peak in early May over the middle shelf, and decay rapidly afterwards, reaching concentration minima in June in both regions. These patters show that earlier ship observations are valid for most of the eastern Bering shelf. Images from August and September 1979 revealed the occurrence of fall blooms, previously unrecorded in this area perhaps because of scarce ship observations after summer. Interannual variation in the distribution of biomass was evident, with April–May 1979 showing less pigment near the surface than April–May 1980. These changes were in part related to aliased sampling by the CZCS. Also, the wind was downwelling favorable in late April 1979 but upwelling favorable during late April 1980. CZCS values underestimated the ship data by a factor of at least 2 during spring 1979. During spring of 1980 the CZCS and ship‐based data were similar. The apparent errors remain unexplained, but it appears that in particular time aliasing of the evolution of the blooms by the CZCS leads to serious problems in comparisons with ship time series. It also seems that region‐specific pigment algorithms are required for proper quantitative interpretation of remote sensing data from the Bering Sea.
Seasonal and nonseasonal variability of satellite‐derived surface pigment concentration in the California Current
Authors: Strub P. Ted , James Corinne , Thomas Andrew C. , Abbott Mark R.
Published: February 2008

Satellite‐derived pigment concentrations from the west coast time series (WCTS) are averaged into monthly mean fields over the California Current system (CCS) for the period July 1979 to June 1986. Errors caused by the scattering algorithm used in the WCTS are reduced by an empirical correction function, although winter values (November–February) remain unreliable. For the March–October period we look at both the mean seasonal development and the nonseasonal monthly anomalies of pigment concentration. These are compared with fields of alongshore wind stress, mixing power of the wind (u*3) and wind stress curl. Outside of the Southern California Bight there is a strong seasonal cycle with a spring‐summer maximum, a northward progression of high pigment concentrations from California to Oregon and a double maximum off Washington (spring and summer, with a lull in between). Within the Southern California Bight, seasonality is low, with a relative minimum in late summer. Off Baja California the pattern is similar to that off northern California. In regions where previous work has been done, there is general agreement with the seasonal cycles found here. Nonseasonal variability in pigment concentration over the large‐scale CCS (400 km wide) is most closely related statistically to synoptic fields of wind stress curl. Within 100 km of the coast, the strongest relations are between pigment concentration and both u*3 and alongshore wind stress. Correlations with these wind variables account for only 25% of the monthly variance in anomalous satellite‐derived pigment concentrations. This is partly due to the noise in both wind and pigment data sets but also demonstrates the fact that much of the anomalous pigment variability is not a response to anomalous wind forcing on these time scales. Correlations are also low between anomalous pigment concentrations and anomalous sea level heights, which serve as a crude proxy for the strength of the alongshore current over the shelf. The largest nonseasonal anomaly in the data occurred during the 1982–1983 El Niño, which caused a large‐scale decrease in pigment concentration, stronger and longer lasting in the south than in the north.
Wind‐forced salt intrusion into a tributary estuary
Authors: Sanford Lawrence P. , Boicourt William C.
Published: February 2008

Moored measurements and hydrographic surveys were carried out during the summers of 1986 and 1987 to examine interaction between the mainstem of the Chesapeake Bay and the Choptank River, an eastern shore tributary estuary. The data show that an important mode of interaction is through wind‐forced intrusion of saline, hypoxic water from below the pycnocline of the Bay into the lower river. Intrusions are driven by lateral tilting of the pycnocline in the Bay, when high salinity water is upwelled on the eastern side of the Bay in response to a southward pulse of wind stress. The resulting internal surges propagate up the relict Choptank entrance channel at a speed of about 20 cm/s and spill onto the broad sill inside the mouth of the river. Intrusion‐favorable pycnocline tilts in the Bay do not always result in lower layer intrusion into the Choptank, but may be blocked or choked in the entrance channel on occasion. The data suggest that wind‐forced intrusion of salt leads to increased gravitational circulation in the Choptank during the summer months, providing a mechanism through which high frequency energy may be directly translated into lower frequency motion.
An automated cloud screening algorithm for daytime advanced very high resolution radiometer imagery
Authors: Simpson James J. , Humphrey Christopher
Published: February 2008

Valid estimates of sea surface temperature (SST) from the advanced very high resolution radiometer (AVHRR) are critically dependent upon the identification and removal of clouds from parent images. Previous cloud‐screening algorithms have demonstrated varying degrees of success, the effectiveness of the particular method used being critically dependent upon cloud type. Contamination from cirrus clouds, for example, has been a major deficiency in previous methods. A robust new algorithm for cloud masking has now been developed which is very effective at removing cloud contamination from images regardless of cloud type. The method, which evaluates every pixel in the image, is statistically reproducible, computationally efficient, and requires no subjective inputs or knowledge of cloud type. The results also show that the algorithm is not regionally specific. The basis for this new method is presented and applications to global AVHRR data, including comparisons with previously used methods, are shown.
The estimation of geoid profiles in the northwest Atlantic from simultaneous satellite altimetry and airborne expendable bathythermograph sections
Authors: Mitchell Jim L. , Dastugue Jan M. , Teague William J. , Hallock Zachariah R.
Published: February 2008

In the NW Atlantic, the temporal mean circulation results in large amplitude surface topography precluding the reasonable use of mean altimetric surfaces or profiles for precise estimation of the geoid. We examine a procedure which (1) uses airborne expendable bathythermograph (AXBT) sections collected along altimeter ground tracks to estimate the single‐pass or instantaneous surface dynamic topography, (2) employs concurrent or simultaneous satellite altimeter overflights to provide a measure of instantaneous sea level, and (3) arrives at a precise estimate of the alongtrack geoid profile by differencing the instantaneous altimetric sea level and the AXBT‐derived dynamic topography. This technique is applied to several Geosat Exact Repeat Mission (ERM) ground tracks in the area of the NW Atlantic Regional Energetics Experiment (REX) using AXBT survey data collected in April and July 1987. Geoid profile estimates are repeatable between these two independent data sets to within 10–20 cm rms. This is near the estimated noise level due to barotropic variability in the Gulf Stream region. These AXBT/Geosat‐derived profiles provide a more consistent estimate of the alongtrack geoid gradient than do available gravimetric geoids. Analysis of the statistics of the ensemble of collinear passes provides an estimate of the geographically uncorrelated orbit error of approximately 1–2 m. The total surface topography derived as the difference between adjusted instantaneous sea level profiles and the AXBT/Geosat‐derived geoid profiles does not suffer significant contamination by either geographically uncorrelated or correlated orbit error.
Physical and biological processes in the North Atlantic during the first GARP Global Experiment
Authors: McClain Charles R. , Esaias Wayne E. , Feldman Gene C. , Elrod Jane , Endres Daniel , Firestone James , Darzi Michael , Evans Robert , Brown James
Published: February 2008

The seasonal cycle of the phytoplankton biomass in the North Atlantic Ocean (20°S to 70°N) is discussed using monthly mean surface pigment concentration fields from the Nimbus 7 coastal zone color scanner (CZCS) for the period of December 1978 through December 1979. The temporal and spatial distributions of surface pigments are compared with quantities derived from the First GARP Global Experiment (FGGE) wind data set (1000‐mbar streamlines, Ekman upwelling, horizontal Ekman transport and |τ|3/2), Climate Analysis Center (CAC) sea surface temperature (SST) fields, concurrent hydrographic station data, and climatological mixed‐layer depths and heat fluxes. The objective of the analysis is to clarify the role of some physical mechanisms that regulate the supply of nutrients to the euphotic zone at different locations in the basin and at different times of the year. It is observed that during this period, the spring bloom was, in most locations, sustained for 2 to 3 months. At a given latitude the onset of the spring bloom varied by several months and, in some cases, could be referred to as a fall bloom. In other cases there were both spring and fall blooms. Time series at 11 selected sites throughout the basin are used to illustrate, in detail, the relation of phytoplankton biomass to local physical forcing. Finally, separate analyses of the mean pigment concentrations for the shelf and open ocean regions indicate that the phytoplankton of both regimes had spring and fall blooms of equal magnitude, the spring bloom being located at northern latitudes and the fall bloom in the equatorial region. Analysis of the open ocean Ekman upwelling field shows similar peaks approximately 2 months in advance of the surface pigment concentration peaks.
Computer simulation of tide‐induced residual transport in a coastal lagoon
Authors: Smith Ned P.
Published: February 2008

A two‐dimensional, four‐layer numerical model of tidally induced residual flow is used to quantify longitudinal transport through the interior of Indian River lagoon, on Florida's Atlantic coast. Water depths and surface slopes at the approximate midpoint between two inlets are calculated by assuming that the tide in the interior of the lagoon is the superposition of exponentially damped sine waves representing six tidal constituents. Tidal waves moving south from one inlet are modified significantly by the same six constituents moving north from a second inlet. The net slope as they pass through each other at the study site quantifies the barotropic pressure gradient. Tidal period variations in longitudinal flow are simulated as a response to the barotropic pressure gradient, vertical eddy viscosity, and horizontal and vertical advective accelerations. The model is tuned and simulations are verified by comparing amplitudes and phase angles with values computed from currents and water levels measured over a 65‐day study period in the summer of 1981. Results indicate a depth‐averaged tidally induced residual flow of 0.8 cm/s at the study site. The residual flow varies from 0.1 to 1.2 cm/s over a synodic lunar month. Just under two thirds of the total is explained by Stokes transport; Eulerian mass transport contributes slightly more than one third. The total mass transport residual current through individual layers decreases from 1.0 cm/s in the top layer to 0.6 cm/s in the lowest 75 cm. An analysis of individual terms in the momentum equation indicates that the force balance is dominated by the barotropic pressure gradient and vertical eddy viscosity forces. The significance of tidally induced residual flow lies in the base‐line level of transport it provides at times of low wind speeds.
Local climatology of wind and sea state by means of satellite radar altimeter measurements
Authors: Tournadre Jean , Ezraty Robert
Published: February 2008

The wind speed and significant wave height (SWH) climatology at a given location of the ocean is a matter of concern in marine technology for planning offshore structures or ship routing as well as in meteorology and oceanography. The purpose of this paper is to present a feasibility study of a new approach to determine the local sea state and wind speed climatology using satellite‐borne radar altimeter. The Geosat data for the first two years (cycles 1 to 43) of the Exact Repeat Mission, and the in situ data from the Quarter Platform (QP) of the Frigg oil field (59°53′N, 2°3′E) in the North Sea have been used for this study. Because of the satellite sampling scheme, a given location of the ocean might never be overflown by the Geosat radar altimeter. Thus, altimetric measurements have to be considered for an area surrounding the location where the climatology is to be estimated. Thus the main question for the determination of the local climatology of wind and SWH is this: given the time and space sampling of Geosat, is it possible to estimate the statistical characteristics of a random process ? Analysis of the Geosat altimeter wind speed and SWH data set over concentric zones surrounding QP Frigg shows that up to 200 km, the SWH and wind speed data set belong to the same population, and that the estimated probability laws are very stable. Comparison of the results of this analysis with the data set of in situ measurements available from QP Frigg during the same period shows that the SWH climatology computed from altimetric measurements in a zone of 100 km radius surrounding the platform is very close to the one computed from in situ data. As compared to the in situ measurements, the wind speed variability is not well represented by the altimetric measurements and the variance estimated from the altimetric data set is lower by more than 20%. This can be attributed to poor signal dynamics with respect to the characteristic noise level in the altimeter wind measurements.
Hy‐wire measurements of atmospheric potential
Authors: Holzworth Robert H.
Published: February 2008

A method of directly measuring the electric potential drop across the lowest portion of the atmosphere by using an apparatus called Hy‐wire is described. This tethered balloon‐borne system has been operated extensively at altitudes near 0.62 km at which voltages over 150 k V were measured with a high impedance device. Also described are measurements of system parameters such as system capacitance (5.6 pf/m), impedance (1010Ω), and response time (tens of seconds). Hy‐wire measurements from an around the‐clock experiment at Wallops Island, Va., having a characteristic repetitive diurnal pattern of variability exceeding 40% of the mean, are presented. This diurnal pattern is discussed in terms of both local and global current sources. A demonstration using Hy‐wire as a lightning channel model is also presented. These experiments have so far been conducted at mid‐latitudes but can also be flown from other locations in an effort to determine whether the lowest atmospheric electric circuit is affected by high altitude and possibly global current systems, and if so how much. The data presented in this paper are not definitive about the source of potential variations. The data are, however, representative of the new Hy‐wire technique and demonstrative of the potential usefulness of this technique.
Correlated optical and electric field signals produced by lightning return strokes
Authors: Ganesh Chidambar , Uman Martin A. , Beasley William H. , Jordan Douglas M.
Published: February 2008

Time‐correlated waveforms of the light radiated from small segments of lightning return stroke channels and of the wide‐band electric fields from the same strokes were obtained for 98 lightning flashes in three Florida storms. The lightning occurred at distances from about 10 km to near or beyond 40 km. The optical system consisted of a photomultiplier tube viewing a collimated slit assembly. The system had a vertical viewing angle of 0.4° (20 dB points) and was aimed 1.2° above the level plane. Light risetimes (10–90%) for 73 first strokes and 70 subsequent strokes varied from about 1 μs to about 60 μs. Nine out of 11 flashes that had three or more strokes and a first‐stroke light risetime less than 12 μs exhibited a statistically significant correlation between either the peak light or the logarithm of peak light and the initial peak electric field for strokes within a flash. Only one out of seven flashes that had three or more strokes and a first‐stroke light risetime greater than 12 μs exhibited this correlation.
The NIMBUS 7 ERB data set: A critical analysis
Authors: Arking Albert , Vemury Sastri
Published: February 2008

An analysis of the first year of the NIMBUS 7 earth radiation budget data set reveals that there are systematic differences between wide and narrow field of view measurements. The larger differences appear in the albedo data and are due primarily to a bias introduced by the processing method. There are smaller differences, associated with the outgoing longwave radiation, which are probably due to errors in calibration. The bias in albedo originates in the factors used for converting the shortwave intensity measured at satellite altitude into a mean daily albedo at the top of the atmosphere. The factor that proves most troublesome is the one that converts measured intensity to the total instantaneous outgoing flux. That factor is determined by angular distribution models, which depend upon the type of scene within the target area. An alternative method of processing the data, which is model independent, is shown to have practically no bias and yields better overall agreement with the wide field of view measurements.