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We estimate the time-averaged velocity field in the North Atlantic from observations of density, wind stress and bottom topography. The flow is assumed geostrophic, with prescribed Ekman pumping at the surface, and no normal component at the bottom. These data and dynamics determine velocity to within an arbitrary function of (Coriolis parameter)/(ocean depth), which we call the “dynamical free mode.” The free mode is selected to minimize mixing of potential density at mid-depth. This tracer-conservation criterion serves as a relatively weak constraint on the calculation. Estimates of vertical velocity are particularly sensitive to variations in the free mode and to errors in density. In contrast, horizontal velocities are relatively robust. Below the thermocline, we predict a strong 0(1 cm/set) westward flow across the entire North Atlantic, in a narrow range of latitude between 25N and 32N. This feature supports the qualitative (and controversial) conjecture by Whist (1935) of flow along the “Mediterranean Salt Tongue.” Along continental margins and at the Mid-Atlantic Ridge, predicted bottom velocity points along isobaths, with shallow water to the right. These flows agree with many long-term current measurements and with notions of the circulation based on tracer distributions. The results conflict with previous oceanographic-inverse models, which predict mid-depth flows an order of magnitude smaller and often in opposite directions. These discrepancies may be attributable to our relatively strong enforcement of the bottom boundary condition. This involves the plausible, although tenuous, assertion that the flow “feels” only the large-scale features of the bottom topography. Our objective is to investigate the consequences of using this hypothesis to estimate the North Atlantic circulation.

Our goal is to develop an air-deployable ocean profiler (ADOP) that will make it feasible to rapidly deploy regional upper-ocean observing arrays. This project's objective is to develop ADOP to be deployed from aircraft through an A-sized (4.875 inch diameter, 36 inches long) sonobuoy tube. The performance goal is 200 dives to 500 m depth with a scientific payload of 1 kg. The float will use Iridium communication and GPS locating while at the surface. ADOP is intended to be the basis for air-deployed arrays that establish persistent area surveillance over regions O(100 km) on a side without post-deployment maintenance.

Pierre Testor(1), Gary Meyers(2), Chari Pattiaratchi(3) , Ralf Bachmayer(4), Dan Hayes(5), Sylvie Pouliquen(6), Loic Petit de la Villeon(6), Thierry Carval(6), Alexandre Ganachaud(7), Lionel Gourdeau(7), Laurent Mortier(8), Herve Claustre(9), Vincent Taillandier(9), Pascale Lherminier(10), Thierry Terre(10), Martin Visbeck(11), Johannes Karstensen(11), Gerd Krahmann(11), Alberto Alvarez(12), Michel Rixen(12), Pierre-Marie Poulain(13), Svein Osterhus(14), Joaquin Tintore(15), Simon Ruiz(15), Bartolomeo Garau(15), David Smeed(16), Gwyn Griffiths(16), Lucas Merckelbach(16), Toby Sherwin(17), Claudia Schmid(18), John A. Barth(19), Oscar Schofield(20), Scott Glenn(20), Josh Kohut(20), Mary Jane Perry(21), Charlie Eriksen(22), Uwe Send(23), Russ Davis(23), Daniel Rudnick(23), Jeff Sherman(23), Clayton Jones(24), Douglas Webb(24), Craig Lee(25), Breck Owens(26)

The autonomous Lagrangian circulation explorer (ALACE) is a subsurface float that cycles vertically from a depth where it is neutrally buoyant to the surface where it is located by, and relays data to, System Argos satellites. ALACEs are intended to permit exploration of large-scale low-frequency currents and to provide repeated vertical profiles of mean variables. ALACEs periodically change their buoyancy by pumping hydraulic fluid from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy. Because positioning and data relay are accomplished by satellite, ALACEs are autonomous of acoustic tracking networks and are suitable for global deployment in arrays of any size. While providing only a sequence of displacements between surfacing intervals, ALACEs are efficient in gathering the widely spaced long-term observations needed to map large-scale average flow. The primary technical challenges met in the ALACE design are maximizing energy efficiency to achieve a l...

[1] Glider surveys of the greater San Pedro Bay region in the Southern California Bight during the fall of 2006 demonstrated the utility of autonomous underwater gliders in a coastal region with complex flow and significant anthropogenic inputs. Three Spray gliders repeatedly surveyed between Santa Catalina Island and the coast of Southern California collecting profiles of temperature, salinity, and chlorophyll fluorescence and estimates of vertically averaged currents. These observations provided context for shelf transport studies during the Huntington Beach 2006 experiment and showed the transition from summer to winter conditions. Vertically averaged currents were predominantly poleward following topography with horizontal scales of approximately 20 km. The gliders surveyed a small cyclonic eddy near Santa Catalina Island and provided a unique view of the structure of the eddy. Nitrate concentration within the euphotic zone was estimated to be 19% greater within the eddy and led to significantly elevated chlorophyll concentrations at the subsurface maximum. Glider observations of salinity reliably detected the distinctly fresh signature of the effluent plume from an ocean outfall near Huntington Beach, California. The salinity anomaly caused by the plume was used to track the spread of the plume as it was advected poleward and away from the coast while remaining subsurface.

The development and implementation of a real-time ocean forecast system based on the Regional Ocean Modeling System (ROMS) off the coast of central California are described. The ROMS configuration consists of three nested modeling domains with increasing spatial resolutions: the US West coastal ocean at 15-km resolution, the central California coastal ocean at 5 km, and the Monterey Bay region at 1.5 km. All three nested models have 32 vertical sigma (or terrain-following) layers and were integrated in conj. unction with a three-dimensional variational data assimilation algorithm (3DVAR) to produce snapshots of the ocean state every 6 h (the reanalysis) and 48-h forecasts once a day. This ROMS forecast system was operated in real time during the field experiment known as the Autonomous Ocean Sampling Network (AOSN-II) in August 2003. After the field experiment, a number of improvements were made to the ROMS forecast system: more data were added in the reanalysis with more careful quality control procedures, improvements were made in the data assimilation scheme, as well as model surface and side boundary conditions. The results from the ROMS reanalysis are presented here. The ROMS reanalysis is first compared with the assimilated data as a consistency check. An evaluation of the ROMS reanalysis against the independent measurements that are not assimilated into the model is then presented. This evaluation shows the mean differences in temperature and salinity between reanalysis and observations to be less than 1 degrees C and 0.2 psu (practical salinity unit), respectively, with root-mean-square (RMS) differences of less than 1.5 degrees C and 0.25 psu. Qualitative agreement is found between independent current measurements and the ROMS reanalysis. The agreement is particularly good for the vertically integrated current along the offshore glider tracks: the ROMS reanalysis can realistically reproduce the poleward California Undercurrent. Reasonably good agreement is found in the spatial patterns of the surface current as measured by high-frequency (HF) radars. Preliminary results concerning the ROMS forecast skill and predictability are also presented. Future plans to improve the ROMS forecast system with a particular focus on assimilation of HF radar current measurements are discussed. Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) Office of Naval Research (ONR) through a subcontract from MBARI to Raytheon ONR’s program element 0601153N for J. Doyle Computational resources for COAMPS were supported in part by the FNMOC.

This review concerns the use of quasi-Lagrangian current-following floats and drifters to observe the ocean and, therefore, involves the union of fluid mechanics and oceanography. Oceanography addresses specific fluid­ dynamical processes as they occur in the world ocean, and one focus of this review is on how free-drifting instruments have led to ocean discover­ ies. The other focus is on the interpretive tools developed to utilize the unique aspects of current followers. The review is addressed to non­ specialists interested in how the ocean is studied. It is intended as a guide to the literature of ocean current followers, emphasizing observations and methods rather than theories or fundamental dynamics. Compared with experimental fluid mechanics, oceanographic methods are limited, and to appreciate Lagrangian ocean studies it is important to understand why. First, the ocean is complex. The individual phenomena are not especially difficult to understand, but there are many going on at any one time. Energetic space scales span ten decades, from I mm to 10,000 km. Time scales range upward from 0.1 s without bound, making separation of mean and variability dubious. The largest scales make up the general circulation, a central topic of oceanography, but its signatures are usually masked by variability. Second, the ocean cannot be controlled; we can observe but not experiment. The system cannot be repeatedly perturbed, nor are observations long enough that pertinent factors repeat. Thus, dynamical inference is indirect, frequently statistical in form, and, because ocean dynamics are nonlinear, ambiguous. Third, the ocean is logistically difficult. The ocean's size and thc expense of operating in it make attended observations discouragingly sparse. The substantial engi­ neering required to make ocean instruments seaworthy also makes them

The prospect for describing advection and eddy transport of tracers in the general circulation using floats is examined. This is done within the context of a recently proposed generalization of the advection-diffusion equation for passive scalars in which eddy transport is governed by a time-dependent eddy diffusivity tensor κ(t) which at large t approaches the constant κ(∞) appropriate to pure advection-diffusion models. A minimal description of the general circulation would include the Eulerian mean velocity U(x) and the diffusivity κ(t). Given sufficient numbers of current-followers which adequately follow ideal fluid particles, both the horizontal components of U and the purely horizontal components of K could be measured. The connection between these transport parameters and statistics of ideal particles shows that if the mean density of the float array is nonuniform then the mean velocity deduced from it will be in error by an array bias produced by downgradient diffusion of floats; this same phenomenon is responsible for the bias of Lagrangian mean velocity away from U toward high eddy diffusivity. A bias also affects diffusivity estimates when the sampling array is not uniform in the mean. The effects of nonuniform sampling make it difficult to piece together an accurate description of the general circulation from floats deployed in localized regional arrays. Both horizontal and vertical separations develop between initially paired floats and fluid particles because floats do not follow vertical water motion. The effect of this on the U and κ measured with floats is examined and is found to be negligible outside of strong currents. With floats, Eulerian statistics must be estimated from a combination of space and time averaging. The uncertainty, σU, of a measured U then depends on the spatial averaging scale A. The trade-off between accuracy and resolution is at the analyst's control by adjusting the averaging scale, but the product σU·λ is fixed by the sampling density and eddy field properties. The measurement uncertainty of the diffusivity κ(t) increases with t, even after κ has reached its asymptote κ∞. Numerical simulation of particle motion is used to test the generalized advection-diffusion equation upon which the development is based, to study how the diffusivity depends on properties of the eddy field, and to explore problems in mapping the general circulation in the presence of statistically inhomogeneous eddies, boundaries and strong currents. When the mean float density is reasonably uniform, then measurements of mean flow and the fully horizontal components of the eddy diffusivity are accurate and are equally useful in strong boundary currents and in broad interior flows.

The investigators goal is to develop the capabilities of autonomous underwater gliders to be maintained and piloted at sea for periods of several months and to exploit this capability to address fundamental questions in ocean science. Underwater gliders are progressing from a developing technology to an operational tool. A major challenge now is to determine what tasks gliders are most suited to perform, a determination that is important to naval operation and to research application. Our objective is to quantify the capabilities of the Spray underwater glider in the field in both Navy and research applications.

My father, an attorney, often commented on the dynamics of legal contests: “More good stories are ruined by an eyewitness. . . .” Over the last 40 years of oceanography to which I have been witness, a similar principle has held. Theory has explained why, and models have simulated, but most of the steps in knowledge have been closely tied to observations. In part, as Walter Munk has often said, this is because “Every time we look at the ocean in a different way we learn something new.” Today, those interested in the large-scale structure and variability of the world’s oceans are blessed with an amazing array of observations with which to work. Satellites provide the most voluminous ocean data with global coverage and have supported some of the most significant increments in understanding the ocean; the first SST images made vivid the different patterns of turbulence in different regions; today altimetry and scatterometry describe evolving dynamically important fields. Over the last half-century a complementary global in situ observing system has been developed and I have been fortunate to observe some of that development. I would like to tell what I know of its story.

The Southern California Coastal Ocean Observing System (www.sccoos.org) is one of 11 eleven regional associations developing an Integrated Ocean Observing System (IOOS) for the United States. IOOS is a recognized initiative identified in the U.S. Ocean Action Plan and is considered one of the U.S. contributions to the Global Earth Observing System of Systems (GEOSS). At the local level, SCCOOS works closely with regional and State mission agencies to develop science-based products to further their work. Agencies include seven different health agencies, three Regional Water Control Boards, major ocean dischargers that include sewer districts and municipalities, private industry including energy producers, marine safety officers, local Navy and Coast Guard personnel, and the commercial shipping industry. Federal funding is leveraged with existing projects with both the State Water Resources Control Board and the California State Coastal Conservancy, including a $21M statewide initiative to map ocean circulation, of which roughly half is invested in SCCOOS. We describe the history of SCCOOS and provide examples of activities presently underway.

As part of the World Ocean Circulation Experiment, 306 autonomous floats were deployed in the tropical and South Pacific Ocean and 228 were deployed in the Indian Ocean to observe the basinwide circulation near 900-m depth. Mean velocities, seasonal variability, and lateral eddy diffusivity from the resultant 2583 float-years of data are presented. Area averages, local function fits, and a novel application of objective mapping are used to estimate the mean circulation. Patterns of mean circulation resemble those at the surface in both basins. Well-developed subtropical gyres, twice as strong in the Indian Ocean as in the Pacific, feed western boundary currents. Tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins, although the Indian subcontinent splits the north Indian tropical gyre. The Antarctic Circumpolar Current (ACC) and west wind drifts are prominent in both basins, generally tending slightly southward but deviating to the north behind the Del Cano, Kerguelen, and Campbell Plateaus and, of course, South America. Remarkably, the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior, away from land. The Indian Ocean’s subtropical gyre, and perhaps part of the South Atlantic’s, reaches east to a retroflection just upstream of the Campbell Plateau south of New Zealand. Seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features. There is a remarkable agreement between the observed seasonable variability and that predicted by the Jet Propulsion Laboratory (JPL)–Estimating the Circulation and Climate of the Ocean (ECCO) data-assimilating numerical model. Aside from seasonal effects, eddy variability is greatest along the equator, in tropical and subtropical western basins, and along the ACC. Integrals of velocity across regional passages (Tasman Sea, Mozambique Channel) provide useful reference for hydrographic analyses of transport. Across whole ocean basins, however, the uncertainty associated with the appropriate continuity relation for horizontal flow (e.g., geostrophy vs nondivergence) is comparable to the mean flow.

This study combines float data from different projects collected between 1991 and 2003 in the South Atlantic to describe the flow of Antarctic Intermediate Water (AAIW). Velocity space-time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry, f/H or f/h (with H being the water depth and It being the thickness of the AAIW layer). When judged by the degree of alignment between respective isolines and the resulting average velocity fields, the best grid is based on a nominal cell size of 3° (latitude) by 4° (longitude) with cell shapes deformed according to f/h. Using this grid, objectively estimated mean currents (and their associated errors), as well as meridional and zonal volume transports are estimated. Results show an anticyclonic Subtropical Gyre centred near 36° S and spanning from 23 ± 1° S to 46 + 1° S. The South Atlantic Current meanders from 33° S to 46° S and shows a mean speed of 9.6 ± 7.8 cm s(-1) (8.5 ± 3.5 Sv; 1 Sv = 1 x 10(6) m(3) s(-1)). The northern branch of the Subtropical Gyre is located between 22° s and 32° S and flows westward with a mean speed of 4.7 ± 3.3 cm s(-1) (9.3 ± 3.4 Sv). Evidence of a cyclonic Tropical Gyre divided in two sub-cells is visible on the stream function. © 2005 Elsevier Ltd. All rights reserved.

Argo is a global array of 3,000 free-drifting profiling floats that measure the temperature and salinity of the upper 2,000 meters of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection. The Argo array provides unprecedented views of the evolving physical state of the ocean. It reveals the physical processes that balance the large-scale heat and freshwater budgets of the ocean and provides a crucial data set for initialization of and assimilation in seasonal-to-decadal forecast models. Argo is central to an unprecedented capability for global assessment of the evolving climate state of the ocean. The thermal structure of the upper ocean controls the temperature of the lower atmosphere, and is the primary variable defining the physical environment of ocean ecosystems. Over 90% of the increased heat content due to global warming of the air/sea/ice climate system in the past 40 years occurred in the oceans. Climate stresses on ocean ecosystems have serious consequences, and sometimes dramatic ones, such as coral reef bleaching. In the future, the impacts of a varying climate on the health of the seas and coastal ecosystems will become an increasingly important aspect of resource management. The unique niche of the Argo array is to provide global broad-scale observations of the upper ocean. This report covers Year 4 of the 5-year project, and builds on progress made by previous awards (Phases 1 and 2) for pilot float arrays, data systems development, and international coordination. In 2005, 450 CTD profiling floats were deployed. Float deployments targeted the Atlantic, Pacific, Indian, and Southern Oceans. Developments in 2005 included deployment of the first operational floats employing Iridium telecommunications and deployment of 22 floats equipped with oxygen sensors.

Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiment's period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.

We aim to provide cost-effective ways to gather physical and bio-physical data over an ocean region with sufficient temporal and spatial resolution to resolve and define mesoscale features using autonomous instruments so that surveillance could be extended indefinitely.

Our long-term goal is to understand the biogeochemical dynamics of the ocean s upper kilometer. Such an understanding is fundamental to prediction of the processes partitioning carbon between atmosphere and ocean and to the redistribution of carbon and associated elements within the water column. Key to predictability is understanding the day-to-day variability of processes governing abundances of carbon species (dissolved and particulate, inorganic and organic) in the water column.

LONG-TERM GOALS. A major oceanographic problem is to understand the biogeochemical dynamics of the upper kilometer of the water column. Such an understanding is fundamental to the predictability of the processes partitioning carbon between atmosphere and ocean and of those redistributing carbon and associated elements within the water column. Key to predictability is understanding day-to-day variability of processes governing abundances of carbon species (dissolved and particulate, inorganic and organic) in the watercolumn. OBJECTIVES. Our objective is to demonstrate the concept of low-cost autonomous profiling vehicles, outfitted with a suite of low-power optical, physical and chemical sensors, which when widely deployed, will permit high frequency - 4D -observations in the upper 1000 m of the variability of ocean biological processes, carbon biomass, upper ocean physics, and parameters of the carbon system. It is envisioned that once proven, such vehicles can be widely deployed to explore carbon biomass variability on global scales.

Publisher Summary This chapter traces the historical context for the World Ocean Circulation Experiment (WOCE) float programme. It discusses the methods and limitations of analyzing Lagrangian measurements along with some of the results gained. The WOCE Float Programme was undertaken by scientists from many different nations. Usage of the three main float types—namely, RAFOS, ALACE, and MARVOR–during WOCE was unevenly distributed. Generally, where a high density of velocity mapping was required or pseudo-Lagrangian trajectories were desired acoustically tracked floats were employed. The float observations needed to carry out the ambitious WOCE plan to accurately map flow globally would have been prohibitively expensive using relatively short-lived acoustically tracked floats needing an array of sound sources. Thus over much of the global ocean WOCE sampling fell to autonomous floats with the consequent loss of continuous tracking. Swallow float has become an observational tool capable of charting the world ocean's subsurface general circulation and providing numerous and economical profiles of ocean properties. Floats essentially have provided visualization of basin-scale flows including intergyre and interbasin transport. In many regions enough observations have been accumulated to produce statistically reliable descriptions of absolute flow from which hydrographic shears can be referenced.

The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation.

We hope to describe deep oceanic convection well enough to critically test and guide models used to predict subsurface ocean conditions. Our objective is to use neutrally buoyant float observations to define statistics of convection plume processes (vertical velocity, temperature fluctuations, etc.) over two cooling seasons. These observations will be compared with model predictions relating typical plume properties to physical parameters (surface buoyancy flux, density stratification. etc.) thereby providing an observational test of the models realism and allowing inadequacies to be identified.

Describe the process of deep oceanic convection well enough to provide critical tests of, and guidance to, models used to predict subsurface ocean conditions. Determine where the water involved in deep convection in the Labrador Sea comes from and where it goes.

Our overall goal in this effort is to develop autonomous instruments to expand the ability of oceanographers to affordably observe the ocean. The objective of this collaboration with Breck Owens of WHOI is to develop a small autonomous glider capable of extended operation using GPS navigation and satellite communication when the glider surfaces. The instrument should be capable of maintaining station for months or occupy an upper ocean section of O(1000 km) in length.

Direct measurements of magnitude of the northward flow of the Malvinas (Falkland) Current have recently been made with two types of Lagrangian platforms: ALACE floats which cycled between 750-m depth and the sea surface, and 100-m drogued surface drifters. Each data set clearly delineates the path of the Malvinas Current, and the vertical shears inferred from them are commensurate with historical geostrophic shears. Velocities from the surface drifters are used here to adjust geostrophic shears from historical measurements, and the results confirm a large transport of the current, as previously implied by numerical models and a regional inverse calculation. At 42°S, the northward transport of the Malvinas Current in the upper 3000 m appears to be about 70 Sv, several times larger than estimates obtained by adjusting geostrophic shears to assumed levels of no motion. This large barotropie component may have significance in the cross-frontal transfer of intermediate and deep waters from the circumpolar current to the adjacent flow regimes in the South Atlantic, and thus on the inter-basin exchange of water masses.

Methods for quantifying transport processes in the ocean are reviewed. Complexity requires separating ocean fields into a deterministic component that is treated in detail and an eddy field to be described statistically. These separations lead to quantitative measures of advection and eddy transport defined in terms of Eulerian or Lagrangian statistics. Relations between quantities measured in these different reference frames and between measurable quantities and model parameters are discussed. The theoretical basis for ocean measurements of lateral advection, lateral eddy transport and diapycnal eddy transport are reviewed and the adequacy of the customary assumptions and approximations used to interpret observations are examined.

A strong October storm generated 0.35-0.7 m/s inertial frequency currents in the 35 m deep mixed layer of a 300x300 km region of the northeast Pacific Ocean. The evolution of these currents were observed for a 23 day period of weak winds following the storm using a combination of 36 surface drifters drogued at 15 m and 3 moorings with acoustic Doppler velocity profilers. These observation, plus a CTD survey, were used to describe the subinertial, geostrophic flow in this same region. Then it was tested whether the linear internal wave theory combined with advection by the measured subinertial currents can explain the observed evolution of the inertial frequency currents.

Earth models in which seismic wave speeds vary only with depth are sufficiently well constrained to accurately locate earthquakes and calculate the paths followed by seismic rays [Engdahl et al., 1998]. The differences between observations and theoretical predictions of seismograms in such onedimensional Earth models can be used to reconstruct the three-dimensional (3-D) wave speed distribution in the regions sampled by the seismic waves by a procedure known as seismic tomography, a technique akin to medical CAT scanning. Caused by thermal, compositional, and textural variations, wave speed anomalies remain the premier data source to fully understand the structure and evolution of our planet [Romanowicz, 2003], from the scale of mantle convection and the mechanisms of heat transfer from core to surface to the interaction between the deep Earth and surface processes such as plate motion and crustal deformation.

Nonseasonal variability of sea level pressure (SLP) and sea surface temperature (SST) in the mid-latitude North Pacific Ocean is examined. The objective is examination of the basic scales of the variability and determination of possible causal connections which might allow prediction of short-term climatic (time scales between a month and a year) variability. Using empirical orthogonal function descriptions of the spatial structure, it is found that SLP variability is concentrated in a few large-scale modes but has a nearly white frequency spectrum. SST variability is spatially complex (being spread over many spatial modes, some of which have small-scale changes) but is dominated by low-frequency changes. The use of linear statistical estimators to examine predictability is discussed and the importance of limiting the number of candidate data used in a correlation starch is underscored. Using linear statistical predictors, it is found that (A) SST anomalies can be predicted from SST observations ...

The present meter is characterized by its very accurate cosine response tourrent vector components of fluid (air or water) velocity parallel to the rotational axes of its propeller-like flow sensors. Structurally, it employs two flow sensors rotatably mounted on a rod or `sting` carried by a casing. Each sensor includes a pair of back-to-back propellers or fans mounted on a single axial shaft rotatably supported by the rod. The rotational axes of the two flow sensors are normal one to the other and also normal to the axis of the rod. Rotation of the fans activates a switch-like arrangement electrically coupled to an up-down counter carried in the casing. Blade rotation in one direction yields an `up` count and vice versa.

Application of statistical estimators to analysis and prediction is examined from the point of view of geophysical fluid dynamics. The fundamental difficulty is that estimators constructed from observational records of limited length (the usual case in GFD) are sensitive to sampling errors in the statistics upon which they are based. To achieve meaningful results, the number of data, or input, parameters must be limited. The relationship between statistical and dynamical models (particularly clear for linear systems) coupled with certain statistical methods are explored with respect to the problem of input parameter selection, both for linear and nonlinear systems. Methods of assessing the effects of sampling errors in hindcasts are discussed and techniques for minimizing these effects in forecasts are evaluated. A method of efficiently condensing statistical models to a few input parameters and transfer functions is given. Finally the steps of hindcast analysis and forecaster construction are di...

The perturbation of a turbulent flow by an organized wavelike disturbance is examined using a dynamical, rather than phenomenological, approach. On the basis of the assumption that an infinitesimal perturbation results in a linear change in the statistics of the turbulence, and that the turbulence is either weak or that the turbulent perturbations are quasi-Gaussian, a method for predicting the perturbation turbulent Reynolds stresses is developed. The novel aspect of the analysis is that all averaging is delayed until the dynamical equations have been solved rather than attempting to find, apriori, equations for averaged quantities. When applied to long-wave perturbations the analysis indicates that the perturbation shear stress is of primary dynamical importance, and that this stress is determined by the principal component of mean shear through a relation which depends on the spectrum of the turbulent velocity component parallel to the gradient of the undisturbed mean velocity (the component perpendicular to the wall in a turbulent boundary layer). Theoretical arguments and observations are used to estimate the form of this spectrum in a constant stress shear layer. This results in a prediction of the constitutive law relating turbulent stress and the mean flow. The law is visco-elastic in nature, and is in agreement with the known constitutive relation for stress perturbations to a constant stress boundary layer; it resembles the eddy viscosity relation used successfully by others in describing perturbations in turbulent flows. The details of the constitutive law depend on how well the turbulence obeys Taylor's hypothesis that phase velocity equals mean flow velocity, and some insight into this question is given.

The Mixed Layer Experiment (MILE) was an examination of the upper-ocean response to meteorological forcing. In Part I of this paper ( Davis, deSzoeke, Halpern and Niiler , 1981, Deep-Dea Research, 28, 1427–1451) temperature and velocity variability observed at two moorings, and the concurrent atmospheric forcing, were described. The one-dimensional heat budget closed satisfactorily and the low-frequency variability of wind stress and upper-ocean transport agreed qualitatively. In this paper, various aspects of the observed ocean response to wind forcing are modeled. For low frequencies a linear statistical model relating wind stress and currents is found; it describes wind-driven velocities parallel to the expected Ekman transport and decreasing with depth. On time scales long compared with a tidal period the rate of change of vertically integrated potential energy agrees well with 0.5 ϱu ∗ 3 , where u ∗ is the friction velocity in water. The response to wind forcing is also simulated using a one-dimensional mixed-layer model based on parameterizing the potential energy balance in terms of ϱu ∗ 3 and turbulent energy production by the interaction of velocity shear and the entrainment stress. Simulations of the MILE data indicate that both processes are important, the latter primarily during the start of wind events. This model also reproduces the major features of the observed statistical relationship between winds and currents.

Accurate measurements of mean Lagrangian displacements of water parcels in the mixed layer are difficult to make because wave forces on objects that float on or near the ocean surface can be easily rectified to produce a unidirectional motion. Here we discuss a design for an ARGOS-tracked drifter that is configured so as to minimize surface wave effects, and present measurements of its water-following characteristics in the California Current system in July 1985 at 15 m nominal depth in a small range of wind and wave conditions. The unique features of the drifter are small, spherically symmetric, surface and subsurface floats (to reduce directional wave forces) and a large, semi-rigid, three-axis symmetric drogue in the shape of a corner-radar reflector (to reduce kiting in shear) that self-deploys from a folded configuration. Relative 1–2 h mean flows of 0.6–2.9 cm s −1 past the drogue were measured with two vector-measuring current meters (VMCM's) attached to the top and bottom of the drogue in the presence of significant wave heights of 0.3–2.2 m, wind speeds of 2–10 m s −1 , and mean vertical shears of 0.34–3.12 × 10 −2 s −1 . A drag force model shows that the most significant forces in the least square sense are due to winds or surface gravity waves, jointly accounting for 74% of the variance. In July 1985, 20 drogues were released in the vicinity of 31°N, 120°W. Although the encapsuled ARGOS transmitter in the small surface sphere submerged a significant portion of time, an average of 5 out 6 possible ARGOS positions were obtained daily. Recovery and inspection of one drifter both 4 and 8 months after deployment in the California Current revealed the conditions of the mechanical components to be excellent.

Variability of near-surface Currents over a 20-Day period in a 15O km diameter region of the central North Pacific is described using vertical profiles from a current meter and the tracks of 25 drifting buoys. Energetic fluctuations of order 0.10 m s−1 having time scales of a few days and vertical scales in excess of 100 m were found, apparently coherent with the wind forcing. Buoy tracks disclose a small-scale (

A technique for the objective analysis of oceanic data has been developed and used on simulated data. The technique is based on a standard statistical result—the Gauss-Markov Theorem-which gives an expression for the least square error linear estimate of some physical variable (velocity, stream function, temperature, etc.) given measurements at a limited number of data points, the statistics of the field being estimated in the form of space-time spectra, and the measurement errors. An expression for the r.m.s. error expected in this estimate is also derived and illustrated in the form of ‘error maps’. Efficient sampling arrays can be designed through trial-and-error adjustment of array configurations until a suitable balance of mapping coverage and accuracy, as measured by the error maps, is achieved. Examples of the mapping ability of some simple arrays are given. Using statistics inferred from the preliminary Mid Ocean Dynamics Experiments various realizations of likely flow fields were simulated. The 16 element MODE-I array was tested by comparison of the simulated fields and the objective maps based on inferred ‘measurements’ at the array points. The reliability of statistics inferred from observations was estimated by comparing correlations derived from limited observations of the simulated fields with the known statistics. Correlations derived from two realizations differed significantly but most calculations reproduced the known statistics moderately well. An intercomparison of Eulerian measurements (current meters) and Lagrangian measurements (neutrally buoyant drifters) was also carried out using the objective interpolation method.

The relationships between sea surface temperature (SST) and sea level pressure (SLP) anomalies over the North Pacific are examined using seasonally stratified statistics. These indicate that autumn and winter SLP anomalies are predictable from prior observations of either SST or SLP. The relationships are a strong function of season and therefore are not detectable in statistics generated by averaging over all seasons. Neither spring nor summer SLP anomalies appear predictable. The patterns of predictable SLP anomalies and the SST and SLP anomalies from which they can be predicted are found as principal estimator patterns. Statistical predictors of autumn and winter SLP anomalies, developed on a 20-year dependent data set, are found to be useful in forecasting a period of 10 other years.

It is shown theoretically that surface waves incident on a beach from deep water can excite edge waves. In particular, a standing wave normally incident on a beach of constant gentle slope is found to transfer energy to edge waves through a weak resonant interaction resulting from an instability of the incident wave with respect to perturbation by edge waves. The analysis is based on the shallow water approximation and ignores the earth's rotation and consequently applies only to relatively low-mode, high-frequency waves. Coupling coefficients, frequencies, and longshore wave numbers of the excited waves are given. In accordance with Hasselmann's (1967) rule, only edge waves with frequencies lower than the frequency of the incident wave are excited by this mechanism. Viscous effects suggest that an edge wave with a frequency one-half that of the incident wave is preferentially excited.

The Mixed Layer Experiment (MILE) was an examination of the upper ocean carried out near Ocean Weather Station P during a 20-day period in the autumn of 1977 characterized by two wind events. In this paper the variability of temperature and velocity observed at two moorings are described and related to the surface heat flux and wind forcing. A one-dimensional upper layer heat budget is found to close acceptably and it is shown that this success depends on having well-sampled temperature records and a method of accounting for vertical velocities in the seasonal thermocline. A similar budget of momentum is also reasonably accurate, but it is necessary to account for the effects of quasi-geostrophic velocities in the upper layer inferentially. Internal waves are found to be a major source of variability, dominating velocity records even at 5-m depth, well within the mixed layer. In the seasonal thermocline there is a high-frequency cut-off of internal wave energy well below the local buoyancy frequency. High-frequency internal wave ‘events’ are identified in the seasonal thermocline. Shear in the upper layer, and its response to wind, have some features in accord with models taking slab flow in the mixed layer, but the agreement is far from complete. Observations in the thermocline indicate that velocity differences in the vertical are maintained only if there is sufficient density stratification to make the Richardson number exceed a critical value.

Linear statistical estimators are used to examine 29 years of nonseasonal, monthly-mean, tide-gauge sea-level data along the west coast of North America. The objective is exploration of the structure, and causes of nearshore ocean variability over time scales of months to years at 20 stations from Alaska to Mexico. North of San Francisco, 50–60% of the sea-level variability reflects a simple inverse barometric response to local atmospheric pressure. These inverted barometer effects account for only 10–15% of the variance at stations to the south. The dominant signal of inverse-barometer-corrected sea level represents a nearly uniform rise or fall of sea level everywhere along the eastern rim of the North Pacific. The interannual aspects of this large-scale sea-level variability are closely related to El Nino occurrences in the eastern tropical Pacific which appear to propagate poloward with phase speeds of ∼40 cm s−1. Higher frequency aspects of this large-scale sea-level variability appear to re...

A simple model is proposed for the creeping motion of a bubble contaminated with an “insoluble” surface-active agent. The existence of a stagnant cap over the rear of the bubble is taken for granted, and the cap size and associated bubble drag are then computed theoretically, as functions of the surface pressure at which the contaminant film collapses. The model, which employs no adjustable parameters, is consistent with experimental observations and, in particular, explains the success of the empirical correlation relating the bubble drag to the Bond number.