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Wind forcing is the main driver of river plume dynamics. Direction and magnitude of wind determine position, shape, and size of a river plume. The response of river plumes on wind forcing was simulated in many numerical modeling studies; however, in situ measurements of this process are still very scarce. In this study, we report the first direct measurements of frontal movement of a small river plume under variable wind forcing conditions. Using quadcopters, we performed nearly continuous daytime aerial observations of the Bzyb river plume located in the non-tidal Black Sea. The aerial remote sensing was accompanied by synchronous in situ measurements of wind forcing. We assessed spreading patterns of the plume and evaluated movement velocity of its outer border with unprecedentedly high spatial (∼10 m) and temporal (∼1 min) resolution, which was not available in previous studies based on in situ measurements and satellite observations. Based on the collected data, we evaluated the time of response of plume spreading dynamics on changes in wind forcing conditions. The advection velocity of the outer plume border shows linear relation to wind speed with very small response time (10–20 min). The reversal between upstream/downstream plume spreading occurs during several hours under moderate wind forcing conditions. These reversals involve only near-field part of the plume, which cause detachment of the far-field part of the plume. The obtained results are crucial for understanding and simulating spreading dynamics of small river plumes worldwide.

Search and rescue (SAR) modeling applications, mostly based on Lagrangian tracking particle algorithms, rely on the accuracy of met-ocean forecast models. Skill assessment methods are therefore required to evaluate the performance of ocean models in predicting particle trajectories. The Skill Score (SS), based on the Normalized Cumulative Lagrangian Separation (NCLS) distance between simulated and satellite-tracked drifter trajectories, is a commonly used metric. However, its applicability in coastal areas, where most of the SAR incidents occur, is difficult and sometimes unfeasible, because of the high variability that characterizes the coastal dynamics and the lack of drifter observations. In this study, we assess the performance of four models available in the Ibiza Channel (Western Mediterranean Sea) and evaluate the applicability of the SS in such coastal risk-prone regions seeking for a functional implementation in the context of SAR operations. We analyze the SS sensitivity to different forecast horizons and examine the best way to quantify the average model performance, to avoid biased conclusions. Our results show that the SS increases with forecast time in most cases. At short forecast times (i.e., 6 h), the SS exhibits a much higher variability due to the short trajectory lengths observed compared to the separation distance obtained at timescales not properly resolved by the models. However, longer forecast times lead to the overestimation of the SS due to the high variability of the surface currents. Findings also show that the averaged SS, as originally defined, can be misleading because of the imposition of a lower limit value of zero. To properly evaluate the averaged skill of the models, a revision of its definition, the so-called SS∗, is recommended. Furthermore, whereas drifters only provide assessment along their drifting paths, we show that trajectories derived from high-frequency radar (HFR) effectively provide information about the spatial distribution of the model performance inside the HFR coverage. HFR-derived trajectories could therefore be used for complementing drifter observations. The SS is, on average, more favorable to coarser-resolution models because of the double-penalty error, whereas higher-resolution models show both very low and very high performance during the experiments., This work was supported by the IBISAR project funded by Mercator Ocean International User Uptake Program under the contract 67-UU-DO-CMEMS-DEM4_LOT7, and the EuroSea European Union’s Horizon 2020 Research and Innovation Program (grant agreement ID 862626). IBISAR was developed in close collaboration with the Spanish Maritime Safety and Rescue Agency and the Spanish Port System. IH-C was supported by the Vicenç Mut grant funded by the Government of the Balearic Island and the European Social Fund. We are also very grateful for the MEDCLIC project (LCF/PR/PR14/11090002) supported by La Caixa Foundation, contributing to the development of the WMOP model.

Coupling between the surface and near‐bottom currents in the Gulf of Mexico (GoM) has been reported in many case studies. However, geographical variations of this coupling need more examination. In this study, surface geostrophic currents derived from satellite‐observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the GoM. The short‐period (30–90 days) fluctuations generated by the Loop Current (LC) and the LC eddies (LCEs) have a more vertically coherent structure and stronger deep ocean expressions than the long‐period fluctuations (>90 days). In addition, the strength of the coupling is modulated by the long‐period variations of the LC and LCE sheddings. Moreover, the surface and bottom coupling varies geographically. In the LC region, the surface fluctuations along the eastern side of the LC are important in causing the bottom current fluctuations through baroclinic instability under the LC and through traveling topographic Rossby waves (TRWs) north of the LC. In the central deep GoM, the bottom currents are affected by the upper fluctuations of the northern LC through both local baroclinic instability and remote TRW propagation. In the northwestern GoM, the bottom current fluctuations are largely related to the remote surface variability from the west side of the LC by TRWs propagating northwestward. This study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties., Key Points Surface and bottom currents in the Gulf of Mexico can be coupled locally by baroclinic instability and remotely by topographic Rossby wavesFluctuations generated along the Loop Current have stronger deep ocean expressions at the period of 30–90 days than at longer periodsSurface and bottom coupling in the Gulf of Mexico varies geographically and is modulated by the Loop Current and the Loop Current eddies

High-frequency radar (HFR) data were used to describe the general surface circulation patterns, including the mesoscale upwelling events of the coastal region located southwest of Lisbon, Portugal. This dynamically complex region has been studied before using scarce measurements of limited duration. The results shown here reveal the capabilities of this measurement system and provide an immense contribution to this field of study, which is now able to profit from longer datasets with both high temporal and spatial resolutions. Hourly radial data quality was assessed by comparing radial velocities from both sites at the baseline midpoint. Spatial gaps were filled using the open-boundary mode analysis (OMA). Low-pass filtered currents were examined using the empirical orthogonal function (EOF) analysis. The results showed that the first three modes represent almost 65% of the total variability and have strong and significant correlations to wind-forcing. The dominant EOF mode captures the Portugal Coastal Current (PCC) reversals. Tidal currents were evaluated using harmonic analysis. The results show that the dominant constituents in this region are M2, S2, N2, and K1. Conditional averaging of upwelling events demonstrates that the pattern has a cross-shore flow that is directed offshore, which reaches steady state after 132 h. Finally, frozen-field trajectories for the upwelling pattern were computed and compared to the mean upwelled plume displacement found using SST data. Outstanding Thesis Lieutenant, Portuguese Navy Approved for public release. distribution is unlimited

The influence of ocean currents on marine population connectivity is critical to territory planning, and such phenomena should be considered in the design and implementation of marine protected areas (MPAs), marine spatial planning strategies, and restoration plans, among other developments. Knowledge of the influence of currents is also vital in understanding the relationship between oceanographic drivers and ecosystem configurations. However, despite their importance, ocean currents and their role in coral connectivity remain poorly constrained in the Seaflower Marine Reserve, an area that hosts the most productive open-ocean coral reef system in the Caribbean and that was declared a biosphere reserve in 2000. We herein characterize the larva transport patterns associated with surface currents that control connectivity in the reserve. To achieve this aim, we simulated the advection of buoyant coral larvae of Acropora palmata during nine spawning events. Larval dispersal patterns were obtained through offline coupling of a high-spatiotemporal resolution hydrodynamic field and a biophysical Lagrangian model for particle dispersion. Ocean current fields were generated using a Regional Ocean Modeling System (ROMS) that was appropriately configured for the region. Larval dispersion was simulated using an Individual-Based Model (Ichthyop). Our results show that there are heterogeneous connectivity patterns during the spawning events at seasonal and inter-annual scales. This seems to be associated with high spatiotemporal dynamic variability in the region, such as the Caribbean Current bifurcation close to the Nicaraguan Rise, the intrusion-formation of mesoscale and sub-mesoscale eddies, and the semi-permanent presence of the Panama-Colombia Gyre. We also found that Serranilla, Providencia, Quitasueño, and Serrana act as the most important sinks. In contrast, the northernmost reefs, Serranilla, B. Alicia, and B. Nuevo, seem to be the most important sources of larvae, highlighting that these areas need to be incorporated into the current MPA zonification and that this could lead to the improvement of MPA effectiveness. Our findings also suggest the need to implement MPA networks between Jamaica and Colombia to allow biological populations to become resilient to environmental changes and less prone to local extinctions.

High Frequency Radar (HFR) technology refers to land based remote sensing instruments capable of measuring surface currents and ocean waves at ranges up to 200 km or more. HFR technology is widely acknowledged as a cost-efficient tool to monitor coastal regions and has potential use to monitor coastal regions all over the world. Globally, the number of HFR stations is steadily increasing. Regional networks provide real-time data in support of operational activities such as search and rescue operations, fast response in case of maritime accidents and spill of pollutants, and resource management. Each operator needs a general understanding of the working principles in order to ensure that instruments are managed properly. A set of harmonized quality assurance and quality control procedures is recommended, along with an effective approach to HFR data discovery and dissemination, to provide high quality measurements to the end users. Different documents providing best practices for operation and maintenance have emerged in the past years. They are oriented either to Direction Finding (DF) or Beam Forming (BF) systems, or to specific manufacturer’s radar systems. The main objective of this paper is to offer a comprehensive “Best Practices” document in an effort of ensuring consistency between different deployments and harmonized operations of HFR systems. This, regardless of system manufacturer, antenna design and setup. A homogeneous approach is given when possible, general concepts and definitions are introduced in order to provide a framework for both data processing and management steps. Examples are also given from the European HFR users with focus on Near Real Time data flow suitable for operational services.

Place: Oxford Publisher: Pergamon-Elsevier Science Ltd WOS:000582696800013; International audience; In the Tropical Atlantic Ocean, we assessed the accuracy of a Lagrangian model (Ichthyop) forced with velocity fields from a hydrodynamical model (CROCO) and two different remote sensing products (GlobCurrent and OSCAR) using trajectories of oceanographic drifters. Additionally, we evaluated the possibility to expand the drifters data using trajectories of GPS-buoy equipped drifting Fish Aggregating Devices (FADs). The observed and simulated trajectories were compared in terms of spatial distribution, velocity distribution and a nondimensional skill score. For the drifters and FADs, the GlobCurrent and OSCAR products lead to similar performances as the CROCO model-ouputs in the broad studied domain. In the Gulf of Guinea, however, the CROCO model performed significantly better than the other two because the parent solution of CROCO benefited from its communication with a child grid of finer resolution in this region. On average, the simulations lead to an underestimation of the drifter and FAD velocities, likely because the spatial resolutions of the forcing products were insufficient and the time frequency at which they were produced were too low to resolve the relevant oceanic processes properly. We found a low skill for all models to simulate FAD trajectories, possibly because of the devices vertical structure that prevent FADs from drifting like water parcels. Our results therefore suggest that in the Tropical Atlantic the FAD dataset may not be appropriate to use for corroborating Lagrangian simulations.

The results of the surface current spatial structure observations performed by SeaSonde Doppler HF radar (operating frequency is 25 MHz) in the Black Sea region adjacent to the city of Gelendzhik are represented. The observations imply a special technique consisting in successive measurements at two selected points of the coastline. Initially, the measurements are carried out in the first of two selected coastal points during two hours. Then the radar system is transferred to the second point on the coast where the procedure is repeated. At that the velocity field is assumed to remain unchanged during the total measurement period (including the time of the radar displacement) from both points. The measurement results are shown in a form of a spatial map of the current velocity vectors in the research region (with 20 × 20 km dimensions). Some features of the current spatial and temporal variability in the coastal waters are revealed. Particularly, the eddy-like formations (the diameter is a few kilometers) which rapidly move and collapse. Since similar eddies are detected using the contact measurement methods, complex and variable structure of the surface currents measured by a radar does not seem to be an artifact. Nevertheless, reliability of the data resulted from the radar measurements of the surface current velocity field should be verified in future by comparing it with the results of the quasi-synchronous velocity field measurements performed by stationary, drifting and towed velocity meters.

The first eXpendable BathyThermographs (XBTs) were deployed in the 1960s in the North Atlantic Ocean. In 1967 XBTs were deployed in operational mode to provide a continuous record of temperature profile data along repeated transects, now known as the Global XBT Network. The current network is designed to monitor ocean circulation and boundary current variability, basin-wide and trans-basin ocean heat transport, and global and regional heat content. The ability of the XBT Network to systematically map the upper ocean thermal field in multiple basins with repeated trans-basin sections at eddy-resolving scales remains unmatched today and cannot be reproduced at present by any other observing platform. Some repeated XBT transects have now been continuously occupied for more than 30 years, providing an unprecedented long-term climate record of temperature, and geostrophic velocity profiles that are used to understand variability in ocean heat content (OHC), sea level change, and meridional ocean heat transport. Here, we present key scientific advances in understanding the changing ocean and climate system supported by XBT observations. Improvement in XBT data quality and its impact on computations, particularly of OHC, are presented. Technology development for probes, launchers, and transmission techniques are also discussed. Finally, we offer new perspectives for the future of the Global XBT Network GG, FB, SD, UR, MB, RD, and DV were supported by a grant from the NOAA/Ocean Observing and Monitoring Division (OOMD) and by NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML). The participation of JS and NZ in this study was supported by NOAA's Global Ocean Monitoring and Observing Program through Award NA15OAR4320071 and NSF Award 1542902. CD was funded by the Australian Research Council (FT130101532 and DP160103130); the Scientific Committee on Oceanic Research (SCOR) Working Group 148, funded by national SCOR committees and a grant to SCOR from the U.S. National Science Foundation (Grant OCE-1546580); and the Intergovernmental Oceanographic Commission of UNESCO/International Oceanographic Data and Information Exchange (IOC/IODE) IQuOD Steering Group. LC was supported by 2016YFC1401800 SI

The Winds and Currents Mission (WaCM) is a proposed approach to meet the need identified by the NRC Decadal Survey for the simultaneous measurements of ocean vector winds and currents. WaCM features a Ka-band pencil-beam Doppler scatterometer able to map ocean winds and currents globally. We review the principles behind the WaCM measurement and the requirements driving the mission. We then present an overview of the WaCM observatory and tie its capabilities to other OceanObs reviews and measurement approaches.

Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satellite-tracked movements of hundreds of drifters deployed by research and voluntary observing vessels provide high-frequency and high-resolution information on near-surface currents around the globe. Consequently, they constitute a major component of the Global Ocean Observing System (GOOS). However, maintaining this array is costly and in some oceanic regions such as the tropics, spatio-temporal coverage is limited. Here, we demonstrate that the GPS-buoy equipped fish aggregating devices (FADs) used in tropical tuna fisheries to increase fish catchability are also capable of providing comparable near-surface current information. We analyzed millions of position data collected between 2008 and 2014 from more than 15,000 FADs and 2,000 drifters, and combined this information with remotely-sensed near-surface current data to demonstrate that the surface velocity components of FADs and drifters are highly correlated in the Atlantic and Indian Oceans. While it was noted that the subsurface structures of FADs (typically made of recycled fishing nets) did slow them down relative to the drifters, particularly in the Atlantic Ocean, this bias was measurable and could be accounted for in future studies. Our findings show that the physical meteorological and oceanographic data collected by fishermen could provide an invaluable source of information to the GOOS. Furthermore, by forging closer collaborations with the fishing industry and ensuring their contributions to global ocean databases are properly acknowledged, there is significant scope to capture this data more effectively.

Physical oceanography is the study of physical conditions, processes and variables within the ocean, including temperature–salinity distributions, mixing of the water column, waves, tides, currents and air–sea interaction processes. Here we provide a critical review of how satellite sensors are being used to study physical oceanography processes at the ocean surface and its borders with the atmosphere and sea ice. The paper begins by describing the main sensor types that are used to observe the oceans (visible, thermal infrared and microwave) and the specific observations that each of these sensor types can provide. We then present a critical review of how these sensors and observations are being used to study: (i) ocean surface currents, (ii) storm surges, (iii) sea ice, (iv) atmosphere–ocean gas exchange and (v) surface heat fluxes via phytoplankton. Exciting advances include the use of multiple sensors in synergy to observe temporally varying Arctic sea ice volume, atmosphere–ocean gas fluxes, and the potential for four-dimensional water circulation observations. For each of these applications we explain their relevance to society, review recent advances and capability, and provide a forward look at future prospects and opportunities. We then more generally discuss future opportunities for oceanography-focused remote sensing, which includes the unique European Union Copernicus programme, the potential of the International Space Station and commercial miniature satellites. The increasing availability of global satellite remote-sensing observations means that we are now entering an exciting period for oceanography. The easy access to these high quality data and the continued development of novel platforms is likely to drive further advances in remote sensing of the ocean and atmospheric systems.

Pencil-beam Doppler scatterometers are a promising remote sensing tool for measuring ocean vector winds and currents from space. While several point designs exist in the literature, these designs have been constrained by the hardware they inherited, and the design is sub-optimal. Here, I present guidelines to optimize the design of these instruments starting from the basic sensitivity equations. Unlike conventional scatterometers or pencil-beam imagers, appropriate sampling of the Doppler spectrum and optimizing the radial velocity error lead naturally to a design that incorporates a pulse-to-pulse separation and pulse length that vary with scan angle. Including this variation can improve radial velocity performance significantly and the optimal selection of system timing and bandwidth is derived. Following this, optimization of the performance based on frequency, incidence angle, antenna length, and spatial sampling strategy are considered. It is shown that antenna length influences the performance most strongly, while the errors depend only on the square root of the transmit transmit power. Finally, a set of example designs and associated performance are presented.

International audience; High Frequency Radar (HFR) is a land-based remote sensing instrument offering a unique insight to coastal ocean variability, by providing synoptic, high frequency and high resolution data at the ocean atmosphere interface. HFRs have become invaluable tools in the field of operational oceanography for measuring surface currents, waves and winds, with direct applications in different sectors and an unprecedented potential for the integrated management of the coastal zone. In Europe, the number of HFR networks has been showing a significant growth over the past 10 years, with over 50 HFRs currently deployed and a number in the planning stage. There is also a growing literature concerning the use of this technology in research and operational oceanography. A big effort is made in Europe toward a coordinated development of coastal HFR technology and its products within the framework of different European and international initiatives. One recent initiative has been to make an up-to-date inventory of the existing HFR operational systems in Europe, describing the characteristics of the systems, their operational products and applications. This paper offers a comprehensive review on the present status of European HFR network, and discusses the next steps toward the integration of HFR platforms as operational components of the European Ocean Observing System, designed to align and integrate Europe’s ocean observing capacity for a truly integrated end-to-end observing system for the European coasts.

The effect of the high frequency (synoptic) variability of wind and heat fluxes upon the surface ocean off south-central Chile (west coast of South America) is investigated using a regional ocean model. We focus our analysis in austral summer, when the regional wind experiences significant day-to-day variability superimposed on a mean, upwelling favorable flow. To evaluate the nature and magnitude of these effects, we performed three identical simulations except for the surface forcing: the climatological run, with long-term monthly mean wind-stresses and heat fluxes; the wind-synoptic run, with daily wind stresses and climatological heat fluxes; and the full-synoptic run, with daily wind-stresses and daily fluxes. The mean currents and surface geostrophic EKE fields show no major differences between simulations, and agree well with those observed in this ocean area. Nevertheless, substantially more ageostrophic EKE is found in the simulations which include synoptic variability of wind-stresses, impacting the total surface EKE and diffusivities, particularly south of Punta Lavapie (37° S), where the lack of major currents implies low levels of geostrophic EKE. Summer mean SSTs are similar in all simulations and agree with observations, but SST variability along the coast is larger in the runs including wind-stress synoptic variability, suggesting a rather linear response of the ocean to cycles of southerly wind strengthening and relaxation. We found that coastal SST variability does not change significantly in the first tenths of kilometers from the shore when including daily heat fluxes, highlighting the prominent role of wind-driven upwelling cycles. In contrast, in the offshore region situated beyond the 50 km coastal strip, it is necessary to include synoptic variability in the heat fluxes to account for a realistic SST variability.

17 pages, 14 figures, 2 tables, We analyze the short-term transition, on time scales of the order of days and weeks, of the surface fields in the coastal transition zone off Northwest Africa, between 15°N and 25°N, during winter and spring 2005 and 2006. This is a complex region characterized by the baroclinic coastal jet north of Cape Blanc, along-shore convergence and water export at the Cape Blanc giant filament, and substantial mesoscale variability between Capes Verde and Blanc. We use the anomalies of the wind impulse and two different coastal upwelling indexes, evaluated off 17°N, 20°N and 23°N, in order to assess the importance of wind forcing in this short-term variability. We also employ daily and weekly surface maps of wind, temperature, surface height and currents to investigate which are the mechanisms that lead to the relatively fast changes in the flow patterns. The coastal baroclinic jet and the Cape Blanc giant filament are ubiquitous features, the two being intrinsically related through the intensity of upwelling off Cape Blanc. Therefore, the strength of both features responds, to a large extent, to the fluctuations of the northeasterly winds; their intensity is greater in spring than winter but during both seasons they experience relatively fast oscillations related to the intermittency of the wind field. The mesoscalar features are visible in the entire domain, with time scales typically of the order of two weeks, but become prominent in the southern region during spring, apparently related to an intense northward coastal jet south of Cape Blanc. © 2013 Elsevier Ltd., This research has been funded by the Spanish Government through Projects MOC2 (ref. no. CTM2008-06438-C02-01) and TIC-MOC (ref. no. CTM2011-28867)

Surface current variability is investigated using 2.5 years of continuous velocity measurements from an high frequency radar (HFR) located in the Ibiza Channel (Western Mediterranean Sea). The Ibiza Channel is identified as a key geographical feature for the exchange of water masses but still poorly documented. Operational, quality controlled, HFR derived velocities are provided by the Balearic Islands Coastal Observing and Forecasting System (SOCIB). They are assessed by performing statistical comparisons with current-meter, ADCP, and surface lagrangian drifters. HFR system does not show significant bias, and its accuracy is in accordance with previous studies performed in other areas. The main surface circulation patterns are deduced from an EOF analysis. The first three modes represent almost 70 % of the total variability. A cross-correlation analysis between zonal and meridional wind components and the temporal amplitudes of the first three modes reveal that the first two modes are mainly driven by local winds, with immediate effects of wind forcing and veering following Ekman effect. The first mode (37 % of total variability) is the response of meridional wind while the second mode (24 % of total variability) is linked primarily with zonal winds. The third and higher order modes are related to mesoscale circulation features. HFR derived surface transport presents a markedly seasonal variability being mostly southwards. Its comparison with Ekman-induced transport shows that wind contribution to the total surface transport is on average around 65 %., A. Lana thanks the financial support from the CSIC-JAE doc program co-funded by the European Social Fund (ESF). J. Marmain is supported by Sur-Baleares Project. A. Orfila thanks the support from ENAP-Colombian Army through several grants. This work has been done thanks to the financial support from JERICO-NEXT project.

The interconnected ocean surface current system involves multiple scales, including basin-wide gyres, fast narrow boundary currents, eddies, and turbulence. To understand the full system requires measuring a range of motions, from thousands of kilometers to less than a meter, and from climate time scales (decades) to daily processes. Presently, satellite systems provide us with global and regional maps of the ocean surface’s mesoscale motion (larger than 100 km). Surface currents are measured indirectly from satellite systems. One method involves using remotely sensed fields of sea surface height, surface winds, and sea surface temperature within a physical model to produce currents. Another involves determining surface velocity from paths of drifting surface buoys transmitted to satellite sensors. Additional methods include tracking of surface features and exploitation of the Doppler shift in radar fields. The challenges for progress include measuring small and fast processes, capturing the vertical variation, and overcoming sensor limitations near coasts. Here, we detail the challenges as well as upcoming missions and advancements in satellite oceanography that will change our understanding of surface currents in the next 10 years.

The Southern Ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region. Recently, a secular trend has been reported in wind stress around the Southern Ocean and it is thought theoretically that the strength of the ACC is closely related to wind stress, so one consequence should be a corresponding increase in ACC transport and hence changes in the rate of the global overturning. There are no long-term data sets of ACC transport and so we must examine other data that may also respond to changing wind stress. Here we calculate surface currents in Drake Passage every seven days over 11.25 years from 1992 to 2004. We combine surface velocity anomalies calculated from satellite altimeter sea surface heights with measured surface currents. Since 1992, the UK has regularly occupied WOCE hydrographic section SR1b across the ACC in Drake Passage. From seven hydrographic sections surface currents are estimated by referencing relative geostrophic velocities from CTD sections with current measurements made by shipboard and lowered acoustic Doppler current profilers. Combining the seven estimates of surface currents with the altimeter data reduces bias in the estimates of average currents over time through Drake Passage and we show that surface current anomalies estimated by satellite and in situ observations are in good agreement. The strongest surface currents are found in the Subantarctic and Polar Fronts with average speeds of 50 cm/s and 35 cm/s, respectively and are inversely correlated, so that maximum westward flow in one corresponds to minimum westward flow in the other. The average cross-sectional weighted surface velocity from 1992 to 2004 is 16.7 ± ; ; ; ; 0.2 cm/s. A spectral analysis of the average surface current has only weakly increasing energy at higher frequencies and there is no dominant mode of variability. The standard deviation of the seven day currents is 0.68 cm/s and a running 12 month average has only a slightly smaller standard deviation of 0.52 ± ; ; ; ; 0.16 cm/s. The Southern Annular Mode (SAM) measures the circumpolar average of wind stress and like the surface currents its spectrum has slightly increased energy at frequencies greater than 1 cpy. A cospectral analysis of these, averaging cospectra of five slightly overlapping 36 month segments improve statistical reliability, suggests that there is coherence between them at 1 cpy with the currents leading changes in the Southern annular mode. We conclude that the SAM and average Drake Passage surface currents are weakly correlated with no dominant co-varying modes, and hence predicting Southern Ocean transport variability from the SAM is not likely to give significant results and that secular trends in surface currents are likely to be masked by weekly and interannual variability.

As shown in the literature, ocean surface circulation can be estimated from sequential satellite imagery by using the maximum cross-correlation (MCC) technique. This approach is very promising since it offers the potential to acquire synoptic-scale coverage of the surface currents on a quasi-continuous temporal basis. However, MCC has also many limits due, for example, to cloud cover or the assumption that Sea Surface Temperature (SST) or other surface parameters from satellite imagery are considered as conservative passive tracers. Also, since MCC can detect only advective flows, it might not work properly in shallow water, where local heating and cooling, upwelling and other small-scale processes have a strong influence. Another limitation of the MCC technique is the impossibility of detecting currents moving along surface temperature fronts. The accuracy and reliability of MCC can be analysed by comparing the estimated velocities with those measured by in situ instrumentation, but the low number of experimental measurements does not allow a systematic statistical study of the potentials and limitations of the method. Instead, an extensive analysis of these features can be done by applying the MCC to synthetic imagery obtained from a realistic numerical ocean model that takes into account most physical phenomena. In this paper a multi-window (MW-) MCC technique is proposed, and its application to synthetic imagery obtained by a regional high-resolution implementation of the Regional Ocean Modeling System (ROMS) is discussed. An application of the MW-MCC algorithm to a real case and a comparison with experimental measurements are then shown.

Two HF radar stations looking seaward were installed along the littoral of the Venetian Lagoon (Northern Adriatic). They operated continuously for 1 year (November 2001–October 2002). The surface current data are obtained at a spatial resolution of about 750 m and are available every hour in a zone whose depths slope gently from the coast down to 20 m. The total area covered is about 120 km 2 reaching cca 15 km offshore. These observations give evidence of the different temporal and spatial scales that characterize the current field. Unlike for the flow in inlets of the Venetian Lagoon, the tidal forcing accounts for only up to 20% of the total variability. The tidal influence from the inlets is felt to about 4–5 km away. Low-frequency signal, associated prevalently to meteorological forcing (through the action of winds and atmospheric pressure) at synoptic time scales, is superimposed on a mean southward flow of 10 cm/s. Formation of small-scale eddies (diameter of about 5 km) to the north and to the south of the Malamocco inlet is observed only during the periods of calm. During strong northeasterly bora and southeasterly sirocco winds, an increase of the along-shore southward current due to geostrophic adjustment is observed in a coastal band. A particularly strong bora event in December 2001 generated an almost uniform flow reaching 30–50 cm/s in the whole investigated area. During sirocco in June 2002, a current reversal toward north and a triggering of inertial motions were observed. Yearlong measurements give an insight into a seasonal variability through a sequence of mean monthly current maps. In November and December, the intensity was the highest (up to 18 cm/s), and the flow structure was almost uniform, with a weak shear in the offshore direction. The weakest mean flow was observed in May 2002, characterized however with a nonuniform distribution over the study zone and suggestions of anticyclonic eddies north and south of the Malamocco inlet. On the other hand, possibly due to the highly variable wind, the eddy kinetic energy in May, associated with both small-scale variability near the shore and inertial oscillations offshore, was maximum for the investigated period.

Lagrangian particle trajectory models based on several altimetry-derived surface current products are used to hindcast the drifter trajectories observed in the eastern Gulf of Mexico during May to August 2010 (the Deepwater Horizon oil spill incident). The performances of the trajectory models are gauged in terms of Lagrangian separation distances (d) and a nondimensional skill score (s), respectively. A series of numerical experiments show that these altimetry-based trajectory models have about the same performance, with a certain improvement by adding surface wind Ekman components, especially over the shelf region. However, their hindcast skills are slightly better than those of the data assimilative numerical model output. After 3 days' simulation the altimetry-based trajectory models have mean d values of 75–83 and 34–42 km (s values of 0.49–0.51 and 0.35–0.43) in the Gulf of Mexico deep water area and on the West Florida Continental Shelf, respectively. These satellite altimetry data products are useful for providing essential information on ocean surface currents of use in water property transports, offshore oil and gas operations, hazardous spill mitigation, search and rescue, etc.

The response of the Adriatic shelf waters to dominant winter winds is analysed: the bora, which is a cold, katabatic wind blowing from the northeast; and the sirocco, which blows from the southeast and brings warm Mediterranean air. Currents and sea-level changes, caused by momentum exchange at the air-sea interface, are simulated using a three-dimensional numerical model. Numerical predictions are verified through comparison with data collected in the area. It is shown that the bora induces a rather complex response of the Adriatic Sea, with sea levels organized in several lows and highs and the current field dominated by the wind-curl effect. The currents are directed downwind under the bora maxima, upwind under the minima. Simulations of the bora-driven sea levels and currents are supported by results of in situ measurements carried out on the Adriatic shelf. Moreover, they are confirmed by an analysis of the Coastal Zone Color Scanner (CZCS) imagery, showing that during the bora episodes highly-productive Po-influenced waters extend from the river mouth in an offshore direction, due to advection by upwind currents. The sirocco piles up water in the North Adriatic and brings about the occurrence of storm surges along the northern shorelines. This process has been documented amply in the literature. According to the present model, the sirocco-driven currents are controlled by two different mechanisms: bottom slope, supporting the existence of a cyclonic and an anticyclonic gyre in the sea; and wind curl, which is a source of cyclonic vorticity in the basin. The data show that the sirocco may reverse the current usually found along the western coast, when the wind-forced current component becomes stronger than buoyancy-driven residual flow.

ISI Document Delivery No.: 645AI Times Cited: 10 Cited Reference Count: 26 Cited References: [Anonymous], 2009, OSTM JAS 2 PROD HDB Anzenhofer M., 1999, 464 OH STAT U BAMBER JL, 1994, INT J REMOTE SENS, V15, P925 Bao LF, 2009, PROG NAT SCI-MATER, V19, P195, DOI 10.1016/j.pnsc.2008.06.017 BARRICK DE, 1985, ADV GEOPHYS, V27, P61 Bowen MM, 2002, J ATMOS OCEAN TECH, V19, P1665, DOI 10.1175/1520-0426(2002)0192.0.CO;2 BROOKS RL, 1997, NASA WFF PUBL BROWN GS, 1977, IEEE T ANTENN PROPAG, V25, P67, DOI 10.1109/TAP.1977.1141536 BROWN S, 2008, COAST ALT WORKSH FEB CHELTON DB, 2001, SATELLITE ALTIMETRY, P1, DOI DOI 10.1016/S0074-6142(01)80146-7 Crocker RI, 2007, IEEE T GEOSCI REMOTE, V45, P435, DOI 10.1109/TGRS.2006.883461 Davis CH, 1997, IEEE T GEOSCI REMOTE, V35, P974, DOI 10.1109/36.602540 Deng X, 2006, J GEOPHYS RES-OCEANS, V111, DOI 10.1029/2005JC003039 Deng X., 2002, MAR GEOD, V25, P249, DOI DOI 10.1080/01490410290051572 GOMMENGINGER C, 2009, COASTAL ALTIMETRY HAYNE GS, 1980, IEEE T ANTENN PROPAG, V28, P687, DOI 10.1109/TAP.1980.1142398 Hwang CW, 2006, J GEODESY, V80, P204, DOI 10.1007/s00190-006-0052-x Labroue S., 2004, MAR GEOD, V27, P453, DOI 10.1080/01490410490902089 Lee H, 2008, J GEODYN, V46, P182, DOI 10.1016/j.jog.2008.05.001 Lee H. K., 2008, TERR ATMOS OCEAN SCI, V19, P38, DOI [10.3319/TAO.2008.19.1-2.37( SA), DOI 10.3319/TAO.2008.19.1-2.37(SA)] MARTIN TV, 1983, J GEOPHYS RES-OC ATM, V88, P1608, DOI 10.1029/JC088iC03p01608 Pavlis N.K., 2008, EARTH GRAVITATIONAL RODRIGUEZ E, 1989, J GEOPHYS RES-OCEANS, V94, P9761, DOI 10.1029/JC094iC07p09761 RODRIGUEZ E, 1988, J GEOPHYS RES-OCEANS, V93, P14107, DOI 10.1029/JC093iC11p14107 Shum C, 2003, MAR GEOD, V26, P335, DOI 10.1080/01490410390253487 U.S. Dept. of Commerce National Oceanic and Atmospheric Administration National Geophysical Data Center, ETOPO2V2 GLOB GRIDD Lee, Hyongki Shum, C. K. Emery, William Calmant, Stephane Deng, Xiaoli Kuo, Chung-Yen Roesler, Carolyn Yi, Yuchan NASA; Ohio State University This research is supported by grants from NASA's Ocean Surface Topography Science Team Program, and from the Ohio State University's Climate, Water, and Carbon Program. We also thank two anonymous reviewers for their constructive comments. 10 TAYLOR & FRANCIS INC PHILADELPHIA MAR GEOD 1; We validated Jason-2 satellite altimeter Sensor Geophysical Data Records (SGDR) by retracking 20-Hz radar waveforms over the California coastal ocean using cycles 7-34, corresponding to September 2008-June 2009. The performance of the ocean, ice, threshold, and modified threshold retrackers are examined using a reference geoid based on Earth Gravitational Model 2008 (EGM08). Over the shallow ocean (depth < 200 m), the modified threshold retracker, which is developed for noisy waveforms with preleading edge bump, outperforms the other retrackers. It is also shown that retracking can improve the precision of sea surface heights (SSHs) for areas beyond 2-5 km from the shore. Although the ocean retracker generally performs well over the deep ocean (depth > 200 m), the ocean-retracked SSHs from some of the cycles are found to be less precise when the waveforms do not conform to the Brown ocean model. We found that the retrackers developed for nonocean surfaces can improve the noisy ocean-retracked SSHs. Among the retrackers tested here, the ice retracker overall provides the most precise SSH estimates over the deep ocean in average using cycles 7-34 in the study region.

The meanders of a baroclinic coastal current in the Northwestern Mediterranean Sea have already been reported in the literature. These meanders can be surrounded by vortices. Such vortices have been observed in the western part of the Gulf of Lions but the location and the mechanism of their formation are poorly documented. In this paper, we use the current measurements of a one-year experiment, which was conducted in the eastern part of the Gulf of Lions to detect and characterize the vortex activity. A vortex detection algorithm based on few velocity data was developed. Current measurements were available at the sea surface (HF radars) and in the water column from 50 to 140 m depth (four current meter moorings). SST images and hydrologic data were also used. Results focus on observations that are coherent 50 m and at the surface. Vortices are anticyclonic, of submesoscale size and present maximal velocities of 30-50 cm/s. The drift speed of the vortices is comparable to but less than the velocity of the Northern Current. These observations enable to estimate the minimum vortex occurrence in this area. The presence of vortex structures is strongly correlated with a specific sequence of wind patterns. (C) 2010 Elsevier Ltd. All rights reserved.

21 pages, 13 figures.-- Printed version published May 2008., Full-text version available Open Access at: http://www.iim.csic.es/~barton/html/pdfs.html, The main components of large-scale circulation of the eastern tropical Pacific were identified in the mid 20th century, but the details of the circulation at length scales of 102 km or less, the mesoscale field, are less well known particularly during summer. The winter circulation is characterized by large mesoscale eddies generated by intense cross-shore wind pulses. These eddies propagate offshore to provide an important source of mesoscale variability for the eastern tropical Pacific. The summer circulation has not commanded similar attention, the main reason being that the frequent generation of hurricanes in the area renders in situ observations difficult. Before the experiment presented here, the large-scale summer circulation of the Gulf of Tehuantepec was thought to be dominated by a poleward flow along the coast. A drifter-deployment experiment carried out in June 2000, supported by satellite altimetry and wind data, was designed to characterize this hypothesized Costa Rica Coastal Current. We present a detailed comparison between altimetry-estimated geostrophic and in situ currents estimated from drifters. Contrary to expectation, no evidence of a coherent poleward coastal flow across the gulf was found. During the 10-week period of observations, we documented a recurrent pattern of circulation within 500 km of shore, forced by a combination of local winds and the regional-scale flow. Instead of the Costa Rica Coastal Current, we found a summer eddy field capable of influencing large areas of the eastern tropical Pacific. Even in summer, the cross-isthmus wind jet is capable of inducing eddy formation., Funding for this project came from the Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico), project 32500-T. ATC is a grant holder of the Sistema Nacional de Investigadores (Ref 12406). Partial funding was also provided by the División de Oceanología of CICESE and by CICESE Unidad La Paz. This work was written during a sabbatical stay at the Instituto de Investigaciones Marinas de Vigo (CSIC, Spain), funded by the Ministerio de Educación y Ciencia (Spain) through the ‘Programa de ayudas para movilidad de Profesores de Universidad e Investigadores Españoles y Extranjeros’ (Ref SAB2004-0212).

A fully coupled atmosphere–ocean model, endowed with a feedback of the ocean model on the atmospheric one, was applied in order to simulate the variations of temperature and sea currents induced by the occurrence of a late-fall episode of intense Sirocco wind over the Adriatic Sea. The coupled model was made up of the RAMS atmospheric model coupled with the DieCAST ocean model with the purpose to obtain more realistic forcing conditions of the lower winds on the underlying sea surface. The two main phenomena highlighted by the simulation are: the genesis of a 10 cm s − 1 north- westward current along the Italian coastline and a general cooling of the entire basin of approximately 1 °C limited to the upper 40 m. The same current shows an offshore anti-cyclonic pattern at different latitude in the whole basin. The results generally agree with experimental data collected by surface drifters released in different regions of the Adriatic Sea as a part of the international DOLCEVITA project, which also includes the same Sirocco episode considered here. The simulated currents represent the drifter trajectories quite accurately, with only few exceptions in the northernmost region of the basin, characterized by shallow water conditions. The simulated SST fields fully agree with the temperature values observed by the same drifters.

International audience; This paper focuses on the invasion by Turbinaria ornata (a brown algae) in the Tuamotu archipelago, French Polynesia [(5-35 degrees S)/(200-230 degrees E)]. Prior to 1980, this alga existed only in the Society and Austral archipelagoes. Between 1985 and 1990, it began to appear in the southern and northern parts of the Tuamotu archipelago. Genetic analyses have been shown not to be appropriate in determining the origin of this algae population. This study investigated the possible ocean drift of floating aggregates of algae. Ocean currents were calculated from satellite data from 1993 to 2001. Their spatial variations as well as their seasonal and interannual variations are described along with calculated drift trajectories. While it was found that mean currents cannot directly transport algae from the Society and Austral archipelagoes to the Tuamotu, the large interannual changes during the El Nino-Southern Oscillation phenomenon produce current reversals that are strong enough to create a transport pathway in a short enough time to allow their survival.

International audience; We used Sea-viewing Wide Field-of-view Sensor (SeaWiFS) to document the seasonal cycle of surface chlorophyll in the western tropical Pacific. Surface waters in this region can be divided into two ecosystems. The western end of the cold, salty waters of the cold tongue with high nutrient low chlorophyll (HNLC) characteristics occupies most of the eastern part Of the region, while warm, fresh, and oligotrophic waters of the warm pool stand in the western part. Nevertheless, disruption of the oligotrophy may show up at different locations. We reconstructed the seasonal cycle of chlorophyll, sea surface temperature (SST), winds, and surface currents from satellite data and satellite-derived products by extracting the annual and semi-annual harmonics of the time series at each grid point. The calculation was done for the 1999-2004 years in order to exclude the consequences of the major 1997-1998 El Nino Southern Oscillation event. The variance explained by the seasonal cycle for this period highlights three regions with high seasonality: (1) The oligotrophy/HNLC transition zone undergoes meridional seasonal displacements. The cold tongue is at its northernmost (southernmost) position during boreal spring (fall). These displacements can be explained in terms of meridional advection of chlorophyll-rich waters and are consistent with the seasonal cycle of the north and south equatorial countercurrents that transport phytoplankton-poor waters. (2) Ocean-color images show seasonal enrichments in the far western north equatorial countercurrent (NECC) area, especially during boreal spring. The chlorophyll maximum coincides with the maximum NECC velocity, follows a SST minimum, and occurs during the upwelling-favorable phase of the wind stress curl. We attribute these enrichments to local upwelling associated with current meandering, horizontal advection from further west, and transport of nutrient-rich waters by the New Guinea coastal undercurrent. (3) Near the Solomon Archipelago, we observe enhancements of chlorophyll concentration southwest of the islands in austral winter, when both the southwestward surface currents and the southeasterly wind stress are strongest. This may be a combination of an island-mass effect and wind-driven upwelling. Horizontal advection from the Solomon area leads to an almost concurrent seasonal chlorophyll enrichment in the northern Coral Sea. In the Gulf of Papua, high chlorophyll concentrations at the same time can be explained by the presence of a strong cyclonic circulation. This study highlights the richness of the response of surface chlorophyll to physical processes at the seasonal time scale in a region usually acknowledged as oligotrophic.

The article of record as published may be found at https://doi.org/10.1029/2003JC001949 The utility of high‐frequency (HF) radar data for improving numerical circulation model predictions is evaluated. Comparisons of the statistical properties of the (CODAR‐type) HF radar data and the observed wind indicate a strong correlation between the dominant alongshore, upwelling‐favoring wind‐forcing and HF radar‐derived surface currents along the central California coastline. Because inadequate knowledge of the wind stress is probably a significant source of error in the model solutions, the idea of using HF radar data to provide corrections to the model wind‐forcing is promising. Different HF radar data assimilation schemes are compared and judged based on the correlations observed between model currents and independent observations from two mooring sites. Analysis of correlation maps between model‐predicted and observed currents indicates a spatial and temporal shift between modeled and observed features. However, the impact of HF radar data assimilation reduces these spatial and temporal shifts. A significant improvement in the correlation between the model and observed subsurface currents is achieved when an Ekman‐layer projection of the corrections is included. In this approach, assimilation of HF radar data produces additional Ekman pumping (vertical velocity) based on the horizontal pattern of model‐observed velocity mismatch at the surface. National Ocean Partnership Program Naval Research Laboratory’s ONR program Office of Naval Research (ONR) Ocean Modeling and Prediction Program 601153N N00014-98WR30170 N00014-99WR-30118 N00014-02WR20086 N00014-00WR-20160

This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, may not be copyrighted. The potential of a method to remotely measure near-surface currents and dominant wave spectra using Interferometric Synthetic Aperture Radar INSAR is demonstrated. INSAR consists of a single conventional SAR augmented by an additional receiving antenna. The phase difference between corresponding SAR image scenes observed by the antennas provides an interferogram directly proportional to the ocean surface velocity field. This direct motion detection by INSAR suggests a significant advance compared with conventional SAR where the response to the moving ocean surface is indirectly related to complex modulation of the surface reflectivity by longer waves and currents. An experiment using an airborne INSAR to measure ocean surface currents and wave fields, compared with simultaneous ground truth measurements using Lagrangian drifters and wave array data was conducted in Monterey Bay. INSAR measured mean current magnitude estimates agree to within 10% compared with conventional measurements. The INSAR image wavenumber spectrum is consistent with the in situ directional spectrum and with predicted numerical refraction model outputs. Wavelength of the observed swells is better agreement (correlation better than 0.9) than wave direction. An attempt to estimate the scene coherence time for L-band SAR was made by taking advantage of the almost simultaneously acquired SAR and INSAR images. The obtained mean scene coherence time (100 msec) is consistent with sparse observed estimates in the literature. http://archive.org/details/interferometrics1094535036 Commander, Israeli Navy Approved for public release; distribution is unlimited.

Published data encoding, data collection, data routing, monitoring, BATHY, TESAC 1st Revised Edition

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