Sea Surface Temperature Images Research Articles

Multiple thermal fronts near the Patagonian shelf break

Eighteen year (1985–2002) sea surface temperature (SST) data are used to study the intraseasonal variability of the Patagonian shelf break front (SBF) in the SW South Atlantic Ocean between 39° and 44°S. The cross‐shelf break SST gradients reveal distinct, previously undocumented thermal fronts located both, offshore and inshore of the SBF. Throughout the year the main SBF, identified as a band of negative SST gradient maxima (relatively strong offshore temperature decrease), forms a persistent feature located closed to the 200 m isobath, while two distinct negative gradient maxima are located inshore and offshore of this location. Daily SST images reveal the presence of three branches of cold waters whose edges delineate the above mentioned fronts. The two offshore branches closely follow lines of constant potential vorticity (f/h) and appear to be associated with the Malvinas Current, while a third branch, located further onshore, is not steered by the bottom topography. South of 40°S the onshore branch forms a quasi permanent front parallel to the SBF.

Tracking oceanic currents by singularity analysis of Microwave Sea Surface Temperature images

In the recent years, the power of employing singularity analysis of scalar variables to perform pattern recognition in complex images has been evidenced. This approach is particularly useful when the image under study corresponds to a scalar variable submitted to a turbulent flow because, in that case, the arrangement of singularity manifolds corresponds to the multifractal hierarchy from the underlying turbulent flow. In this paper we will show how this intimate connection between Image Processing and Physics, when applied to Microwave Sea Surface Temperature images, allows to uncover global circulation patterns in the ocean at a daily basis with the resolution of 1/4 of degree. Using this technique, details not evidenced in the non-processed image are revealed. The emerging patterns provide a description of the global oceanic currents much richer than the usual global circulation scheme; in particular, instabilities, eddy generation and filamentation are distinctly identified. A pattern extraction of this kind is useful in order to measure and track mesoscale oceanic phenomena, opening the way to many operational and reanalysis applications.

Retrieving ocean surface current by 4-D variational assimilation of sea surface temperature images

In this article we propose a new method to estimate ocean mesoscale structures of the surface current velocity by processing sea surface satellite images. Assuming that the intensity level can be described by a transport–diffusion equation, the proposed approach is based on variational assimilation of image observations within a simple transport–diffusion model. This approach permits to retrieve the current velocity field from a sequence of satellite images. Results of processing synthetic data and real NOAA-AVHRR satellite images are presented and commented.

Oceanic water intrusion into Kagoshima Bay resulting in thermal stratification

Kagoshima Bay is an enclosed bay that has the tendency to undergo eutrophication, and a very important site to describe the behavior of open seawater intrusion. According to the results of the satellite SST (Sea Surface Temperature) image analysis or numerical simulation focused on the warm water intrusion into the bay in winter, a warm water mass originates in the meandering Kuroshio Current and reaches the mouth of the bay making the density flow to act like a semi-geostrophic current that is influenced by the Coriolis effect. However, there is still no information on the oceanic intruding flow during the summer, where it is accompanied by thermal stratification. In this research, satellite remote sensing and numerical simulation were employed to investigate the oceanic water intrusion into Kagoshima Bay during the summer season by using satellite chl-a (chlorophyll-a) images instead of SST. As a result, the distribution of the low-concentration chl-a with the oceanic water intrusion was found to be similar to the intrusion that occurs during the winter season. Furthermore, the numerical simulation was performed under the simple assumption that the thickness of the warm water mass that reaches the southern coast of Kyushu also shows the same tendency as in the winter season. Although the characteristics, such as the intruding speed or intruding pattern, are similar in winter, some features such as the generation of the inflow from the middle layer, showed a different tendency.

On the nature of oceanic eddies shed by the Island of Gran Canaria

We use hydrographic and buoy data to compare the initial temperature fields and Lagrangian evolution of water parcels in two vortices generated by the southward flowing Canary Current passing around the island of Gran Canaria Island. One vortex is anticyclonic, shed in June 1998 as the result of an incident current of about 0.05 m s −1, and the second one is cyclonic, shed in June 2005 with the impinging current estimated as 0.03 m s −1. The two vortices exhibit contrasting characteristics yet display some important similarities. The isopycnals are depressed in the core of the anticyclonic vortex, at least down to a depth of 700 m, whilst they dome up in the core of the cyclonic vortex but only down to 450 m. In the top 300 m the depression/doming of the isotherms is similar for both vortices, with a maximum vertical displacement of the isotherm of about 80 m, which correspond to temperature anomalies of some 2.5 °C at a given depth. A simple method is developed to obtain the initial orbital velocity field from the temperature data, from which we estimate peak values of 0.7 and 0.5 m s −1 for the anticyclonic and cyclonic vortices, respectively. The buoys, three for the anticyclonic vortex and two for the cyclonic one, were drougued at 100 m depth, below the surface mixed layer, and their initial velocities are consistent with the above values. In both vortices, the buoys revolve either within a central core, where the rotation rate remains stable and large for several weeks, or in an outer ring, where the rotation rate is significantly smaller and displays large radial fluctuations. Within the inner core the anticyclonic vortex has significant inward radial velocity, while the cyclonic vortex has near-zero radial mean motions. The cyclonic vortex rotates more slowly than the anticyclonic, their initial periods being 4.5 and 2.5 days, respectively. A simple axisymmetric model with radial diffusion (coefficient K h≅25 m 2 s −1) and advection reproduces the observations reasonably well, the diffusive effect being more important than that resulting from the observed radial advection. The model also supports the hypothesis that the rotation rate of cyclonic vortices is less than that of anticyclonic vortices, as otherwise they would become inertially unstable. Both the buoys data and sea surface temperature images confirm that the vortices evolve from youth to maturity, as the cores shrink and the outer rings expands, and then to a decay stage, as the core rotation rates decrease, though frequent interactions with other mesoscale structures result in more accelerated aging. Despite these interaction they last many months as coherent structures south of the Canary Islands.

An Operational Circulation Modeling System for the Gulf of Maine/Georges Bank Region—Part II: Applications

This paper describes the implementation of a prototype operational system for providing near-real-time information on the ocean water property and circulation environment in the Gulf of Mexico (GOM)/Georges Bank (GB) region. This application of the Harvard Ocean Prediction System (HOPS) model to the Advanced Fisheries Management Information System (AFMIS) was developed and tested during a 52-week sequence of weekly nowcast/forecasts. The initial assimilation format for a single sea surface temperature (SST) image was expanded to accommodate the assimilation of a trio of SST images, which produced a more realistic thermocline. The model system was applied to the winter-like conditions of March 2002 and the summer-like conditions of August 2002, when the model temperature and velocity fields could be compared with moored time-series measurements at several locations. This data assimilation model system produced qualitatively correct ocean temperature and flow patterns. During late winter, the wind dominated the variability of the model ocean surface Ekman transport, GB north flank jet, and Maine Coastal Current. During late summer, the assimilation of very warm SST dominated the variability of the model coastal upwelling, a stronger and more stable GB north flank jet, and Maine Coastal Current. The model did reveal a persistent anticyclone in the western central GOM that has not been well documented. Quantitatively, the surface temperatures from the model converged with those measured by the Gulf of Maine Ocean Observing System (GoMOOS) within 4-6 d from the beginning of the model run. Further, while the variability of the model and observed temperatures generally tracked each other, there were cases in which differences between contemporary and climatological temperatures led to systematic offsets. The model/observation velocity comparisons, while in general not as good as those for temperature, did improve after 6-8 d and the assimilation of two SST images. Thus, future work is needed to better understand the quantitative model/observation differences revealed by intercomparisons and to improve the initialization and assimilation protocols.

CARACTERIZACIÓN DE LA TEMPERATURA SUPERFICIAL DEL MAR Y CLIMATOLOGíA DE LA BAHíA DE LA PAZ, B.C.S., MÉXICO

Se analizaron 4175 imágenes diarias captadas con el sensor NOAA/AVHRR de julio de 1997 a diciembre de 2004, con el propósito de caracterizar la climatologí­a y variación interanual de TSM en la Bahí­a de La Paz. A partir de la información se generaron 88 meses de anomalí­as de TSM y se realizó un análisis de componentes principa les (CP). Se obtuvieron tres componentes que explican en su conjunto el 50.32% de la varianza total de los datos originales de anomalí­as (32.68%, 11.95% y 5.69% respectivamente). El CP1 presenta los valores de correlación más altos al noroeste de la bahí­a, con un gradiente decreciendo hacia el sureste. Este componente tiene una alta correlación espacial con la batimetrí­a de la bahí­a, y temporal con respecto a los meses cálidos. Los valores más altos del CP2 se sitúan en el centro de la bahí­a, decreciendo hacia el noroeste y sureste. Este patrón espacial se ubica en la zona en la que se ha detectado un gran girociclónico, por lo que atribuimos a este componente la influencia de tal efecto de circulación. El CP3 sitúa sumás alta correlación a lo largo de la costa oeste de la bahí­a, zona fuertemente influenciada por la corriente litoral a lo largo de la costa. Las fluctuaciones en la TSM en la zona y el perí­odo de estudio, no presentaron una correlación significativa con respecto al Indice Oscilación Sur y el Indice El Niño Oscilación Sur, probablemente debido a que la Bahí­a de La Paz tenga rasgos batimétricos y oceanográficos que determinan una respuesta peculiar a los cambios ambientales. Characterization of the sea surface temperature and climatology of the Bay of La Paz, B.C.S., Mexico 4175 daily NOAA/AVHRR sea surface temperature (SST) images from July of 1997 to December of 2004 were analyzed, in order to characterize the climatology and interannual variation of SST in the Bay of La Paz. From this information, 88 months of SST anomalies were estimated and principal components (PC) analysis was performed. Three components were obtained that explain as a whole the 50.32% of the total variance of the original data of anomalies (32.68%, 11.95% and 5.69% res pectively). PC1 displays the higher values of correlation to the northwest of the bay, with a gradient decreasing to wards the southeast. This component has a high spatial correlation with the bathymetry of the bay, and temporal to the warm months. The highest values of PC2 are located in center of the bay, decreasing to wards the northwest and southeast. This spatial pattern is located in the zone where a large cycloniceddy has been detected. For this reason we attributed this component the influence of such circulation effect. PC3 higher correlation lies throughout the westcoast of the bay, a zone strongly influenced by the long shore current. The SST fluctuations in the zone and the period of study did not display a significant correlation with respect to the Southern Oscillation Index or El Niño Southern Oscillation, probably because the Bay of La Paz is an area with bathymetric and oceanographic characteristics that determine a peculiar response to environmental changes.

Composition and distribution of phytoplankton with size fraction results at southwestern east/japan sea

Abundance and distribution of phytoplankton in seawater at southwestern East/Japan Sea near Gampo were investigated by HPLC analysis of photosynthetic pigments during summer of 1999. Detected photosynthetic pigments were chlorophyll a, b, c1+2 (Chl a, Chl b, Chl c1+2), fucoxanthin (Fuco), prasinoxanthin (Pras), zeaxanthin (Zea), 19’-butanoyloxyfucoxanthin (But-fuco) and beta-carotene (β-Car). Major carotenoid was fucoxanthin (bacillariophyte) and minor carotenoids were Pras (prasinophyte), Zea (cyanophyte) and But-fuco (chrysophyte). Chl a concentrations were in the range of 0.16-8.3/land subsurface chlorophyll maxima were observed at 0-10m at inshore and 30–50 m at offshore. Thermocline and nutricline tilted to the offshore direction showed a mild upwelling condition. Results from size-fraction showed that contribution from nano+picoplankton at Chl a maximum layer was increased from 18% at inshore to 69% at offshore on average. The maximum contribution from nano+picoplankton was found as 87% at St. E4. It was noteworthy that contribution from nano+picoplanktonic crysophytes and green algae to total biomass of phytoplankton was significant at offshore. Satellite images of sea surface temperature indicated that an extensive area of the East/Japan Sea showed lower temperature (<18 °C) but the enhanced Chl a patch was confined to a narrow coastal region in summer, 1999. Exceptionally high flux of low saline water from the Korea/Tsushima Strait seemed to make upwelling weak in summer of 1999 in the study area. Results of comparisons among Chl a from SeaWIFs, HPLC and fluorometric analysis showed that presence of Chl b cause underestimation of Chl a about 30% by fluorometric analysis but overestimation by satellite data about 30-75% compared to HPLC data.

Wintertime sea surface temperature fronts in the Taiwan Strait

We present wintertime variations and distributions of sea surface temperature (SST) fronts in the Taiwan Strait by applying an entropy‐based edge detection method to 10‐year (1996–2005) satellite SST images with grid size of 0.01°. From climatological monthly mean maps of SST gradient magnitude in winter, we identify four significant SST fronts in the Taiwan Strait. The Mainland China Coastal Front is a long frontal band along the 50‐m isobath near the Chinese coast. The sharp Peng‐Chang Front appears along the Peng‐Hu Channel and extends northward around the Chang‐Yuen Ridge. The Taiwan Bank Front evolves in early winter. As the winter progresses, the front becomes broad and moves toward the Chinese coast, connecting to the Mainland China Coastal Front. The Kuroshio Front extends northeastward from the northeastern tip of Taiwan with a semicircle‐shape curving along the 100‐m isobath.

Effects of the Yellow Sea Warm Current on the winter temperature distribution in a numerical model

The temperature distribution and circulation patterns in the Yellow Sea (YS) are examined by using a wave‐tide‐circulation coupled numerical model. This model sufficiently reproduces the variation of the warm tongue structure of the Yellow Sea Warm Current (YSWC) from the double branches flowing along the YS Trough and the western 60 m isobath in January to the single stream along the western temperature front in March. This is observed in both the long‐term monthly climatology and the satellite‐based sea surface temperature images in recent years. Examining the local heat balance in the numerical model during the entire cooling period, it is found that the YSWC has a very important influence on the YS warm tongue structure. Compared with the surface cooling, the influence of the advection is small in the coastal shallow area but large in the deep warm tongue area (up to 50% of the magnitude of heat flux). Although bathymetry is the essential factor which causes the temperature front, the YSWC is the key factor which positions, shapes, and maintains the warm tongue structure. This helps to affirm the existence of the YSWC, at least as a monthly mean flow. However, more high‐resolution current observations in deeper layers west of Cheju Island and the western fork of the YS Trough are needed to confirm the existence of the YSWC and its characteristic timescale in the real YS.

Observation and modelling of natural retention structures in the English Channel

Accumulation of heat, or dissolved substances (nutrients, pollutants, etc.), or fine suspended particles in a water body is a key process in the functioning of aquatic ecosystems and their resistance to perturbations. In complex and wide open environments such as marine ecosystems, net accumulation is not only linked to the local renewal capacity of the water body, but also to the partial recirculation of water due to convective cells of various sizes. The English Channel, which can be considered as mainly dominated by tidal movements, exhibits such a complex quasi-permanent long-term circulation, made of a central “river” bordered with a lot of nested gyres. Here, we show that structures visible on satellite images of SST (Sea Surface Temperature), chlorophyll and SPIM (Suspended Particulate Inorganic Matter) can be explained by steady state distributions of tracers having various half-life durations, which can be computed using a simple technique of regularly distributed micro-injection in the permanent flow field. Gyres induced by capes in open water appear to be retention areas, whereas gyres around islands (Channel Isles) appear to be strong disseminating areas, acting as slings. Moreover, SST satellite maps can be explained by a short-lived tracer during the “transitory” seasons (spring and autumn), and by a long-lived one during the “stable” seasons (summer and winter): long-term accumulation structures become apparent only in August and March. SPIM can be considered as a tracer injected only in muddy areas by the bottom friction caused by the swell, and having a half-life duration linked to the turbulent energy dissipation, which controls the settling rate; this succeeds to explain the observed turbidity in the central Channel essentially, as well as the striking asymmetry visible on images between the large turbid coastal band along the English coasts (materializing a natural long-term retention area), and the rather clear waters along the French coasts. The annual mean chlorophyll distribution in the Channel, as derived from satellite reflectance, can be simulated by a short-lived tracer injected proportionally to the mean light availability along the water column. Computing steady state distributions of various substances or particles in permanent circulation gives a simple and quick tool for understanding their mean stable distribution patterns in the oceans.

Automated Thematic Registration of NOAA, CoastWatch, and AVHRR Images

Daily for the United States, the National Oceanic and Atmospheric Administration (NOAA), CoastWatch Program produces multiple regional daytime images and sea surface temperature (SST) images derived from Advanced Very High Resolution Radiometry (AVHRR). Images have 1.1 km pixel resolution at nadir, <1 pixel systematic error (rotation, scale, distortion), but up to 9 pixels translation (offset) error. New fully-automated registration to a reference map corrects translation error to mean radial error <1 pixel suitable for full pixel resolution application in inshore waters and large estuaries. The approach converts AVHRR Channel 1 and 2 data to a land and water thematic image, finds the offset to maximize classification accuracy, and repositions the AVHRR and SST images. Registration was robust to cloud cover and missing data and was more reliable than manual registration for cloudy images. Developed for the southeast region of the U.S., the approach is transportable to other regions.

Spatial and temporal variability of the Brazil‐Malvinas Confluence and the La Plata Plume as seen by SeaWiFS and AVHRR imagery

Ocean color (OCTS, SeaWiFS) and sea surface temperature (AVHRR) images were used to evaluate spatial and temporal variability of the Brazil‐Malvinas Confluence and La Plata Plume (20° to 45°S and 40° to 65°W). The data set covers the period from January 1997 to June 2003. Chlorophyll and SST data were combined using Principal Component Analysis (PCA). The results yielded were used to identify and follow front displacements. PCA maps showed a close relationship with previous observations of currents behavior and the La Plata Plume. Firstly the analysis was performed on data retrieved from a monthly climatology, and the results show three remarkable features: a gradual increase of the northward intrusion of the La Plata Plume throughout the period lasting from summer to winter; the summer shape of the La Plata Plume showed a stronger penetration over the shelf on the Argentinean side of the estuary mouth; and the seasonal migration of the Brazil‐Malvinas Confluence. Monthly composites were then used and compared with discharge and wind data from scatterometers. The results show that increases on discharge led to a greater influence of the La Plata Plume over the continental shelf although during 1998 (El Niño) it did not penetrate farther north because of the unfavorable wind pattern (northerly). On the other side, during 2002, high discharge rates were associated with strong southerly winds, leading to a northern penetration of the plume. The same analysis was applied to daily images to show its application on locating the front's position. This analysis showed the same patterns.

Determining prey distribution patterns from stomach‐contents of satellite‐tracked high‐predators of the Southern Ocean

The distribution of many cephalopod, crustacean and fish species in the Southern Ocean, and adjacent waters, is poorly known, particularly during times of the year when research surveys are rare. Analysing the stomach samples of satellite‐tracked higher predators has been advocated as a potential method by which such gaps in knowledge can be filled. We examined the viability of this approach through monitoring wandering albatrosses Diomedea exulans at their colony on Bird Island, South Georgia (54°S, 38°W) over the winters (May–July) of 1999 and 2000. At this time, these birds foraged in up to three different water‐masses, the Antarctic zone (AZ), the sub‐Antarctic zone (SAZ) and the sub‐Tropical zone (STZ), which we defined by contemporaneous satellite images of sea surface temperature. A probabilistic model was applied to the tracking and diet data collected from 38 birds to construct a large‐scale map of where various prey were captured. Robustness/sensitivity analyses were used to test model assumptions on the time spent foraging and relative catch efficiencies and to evaluate potential biases associated with the model. We were able to predict the distributions of a wide number of cephalopod, crustacean of fish species. We also discovered some of the limitations to using this type of data and proposed ways to rectify these problems.

Classifying and Forecasting Coastal Upwellings in Lake Michigan Using Satellite Derived Temperature Images and Buoy Data

Coastal upwellings are common in the Great Lakes but have lacked enumeration and systematic classification of spatial extent, frequency, duration, and magnitude. Near real-time sea surface temperature (SST) images derived from the Advanced Very High Resolution Radiometer (AVHRR) provide indices of upwelling events, but visual inspection of daily images can be tedious. Moreover, the definition of what constitutes an upwelling from AVHRR data is subjective. We developed a semi-automated method to classify upwellings during the period of thermal stratification using daily, cloud-free surface temperature charts from AVHRR SST data. Then we statistically evaluated the location, frequency, magnitude, extent, and duration of upwelling events in Lake Michigan from 1992–2000. Further, we analyzed meteorological data from the National Data Buoy Center buoys in an attempt to improve the reliability of the classification and to provide a means for future forecast of coastal upwelling. Although variable, upwelling events along the western shoreline were preceded by 4 days of southerly and west-to-northwesterly winds, while upwelling events occurring along the eastern shore were preceded by 4 days of northerly winds. Probability of an upwelling event occurring was a function of the direction-weighted wind speed, reaching a 100% probability at direction weighted wind speeds of 11 m s −1 for the western shore. Probability of an upwelling occurrence along the east coast reached 73% at 11 m s −1 and 100% at 13 m s −1. Continuous measurements of wind data with a sufficient temporal resolution are required during the entire upwelling season to improve the predictability of upwellings.

Modification of surface winds near ocean fronts: Effects of Gulf Stream rings on scatterometer (QuikSCAT, NSCAT) wind observations

Modifications to surface winds by currents and sea surface temperature (SST) gradients near frontal boundaries of Gulf Stream rings are analyzed using satellite SST and scatterometer (NASA's Quick Scatterometer (QuikSCAT), NASA scatterometer (NSCAT)) wind observations. A component of scatterometer wind approximately equal and opposite to the surface current vector is observed and attributed to the fact that scatterometers detect relative motion of water and air. Warm‐core ring (WCR) SSTs act to destabilize the marine atmospheric boundary layer (MABL), increasing surface wind magnitude by 10–15% and decreasing veering angle by 5–15° relative to large‐scale mean winds. Cold‐core ring (CCR) SSTs cause impacts of similar magnitude and opposite sense. Magnitudes and directions of modifications are accounted for by MABL dynamics of a nonlinear planetary boundary layer model forced by air‐sea temperature differences. Wind modifications occur within tens of kilometers of SST fronts, implying a wind response timescale of order 1 hour. By contrast, uniformity of modified winds across the larger area within rings suggests the response time for the MABL to return to equilibrium downstream from a front exceeds 10 hours. Over WCRs, strong divergence (convergence) occurs on the upwind (downwind) side; curl is strongly negative (positive) to the right (left) side facing downwind. Opposite patterns are generally seen over CCRs. Divergence (curl) peaks where winds blow perpendicular (parallel) to SST fronts. SST image analysis indicates enhanced cloudiness occurs with downwind convergence over WCRs. Wind stress curl due to ring modifications causes dipolar Ekman pumping sufficient to influence ring translation and decay processes.

Near-surface thermal structure and surface diurnal warming in the Adriatic Sea using satellite and drifter data

An extensive set of in situ temperature data collected by surface drifters is combined with satellite-derived sea surface temperature images to study the difference between the pseudo-bulk and bulk temperatures (Δ T pb–b) in the Adriatic Sea for the period 21 September 2002–31 December 2003. The variations of this temperature difference are described as a function of local wind speed and incoming solar radiation provided by a local area atmospheric model. The daily sea surface temperature variability is also assessed by computing the temperature difference between the daily maximal and minimal values (Δ T day–night). The data show that the smaller the wind speed and the larger the solar radiation, the larger Δ T pb–b. The temperature difference reached the highest value (∼5 °C) on a hot day (more than 600 W/m 2) of May 2003 in weak wind condition (around 3 m/s). For strong winds (speed > 6 m/s) the dependence on both the wind and solar radiations vanishes as the temperature difference approaches zero because the near-surface water becomes thermally homogenous due to the wind-induced vertical mixing. Strong diurnal warming of the sea surface, as derived by the pseudo-bulk estimates, and a strong near-surface stratification were found during the spring/summer season. Monthly mean statistics show that the diurnal cycle of the pseudo-bulk and bulk temperature starts to become significant already in February and March. Subsequently (from April to August) both the diurnal warming and the stratification are maximal (monthly means of Δ T day–night ∼1–2 °C and of Δ T pb–b ∼0.5 °C ), while in fall and early winter the Δ T pb–b values are quite small (monthly means near 0 °C) and the Δ T day–night monthly means are bounded by 0.5–1.5 °C. Maximal amplitudes of the diurnal cycle can exceed 4 °C (mostly in spring–summer) for both the pseudo-bulk and bulk temperatures. However, the monthly means of Δ T day–night is generally twice as large for the pseudo-bulk estimates (∼2 °C) with respect to the bulk layer (∼1 °C). The diurnal warming of the sea surface, as derived by the pseudo-bulk temperature, occurs at about 14:30 local time, that is more than 2 h after the maximal sun elevation and an hour earlier than the bulk temperature maximum at 20–40 cm depth.

Multi-sensor satellite and in situ measurements of a warm core ocean eddy south of the Brazil–Malvinas Confluence region

A warm core eddy was detected south of the Brazil–Malvinas (Falkland) Confluence (BMC) region in satellite images of the southwestern Atlantic Ocean in late 2002. The structure was also sampled by in situ instruments deployed by a ship in 2 days of November 2002. An analysis of satellite data was performed to account for the lifecycle, dimension, surface temperature, surface chlorophyll concentration, surface height anomaly and displacement of the eddy since it was detached from the Brazil Current in September 2002. Satellite data were derived from several sources such as the AMSR-E, MODIS and radar altimeter. The structure lasted 64 days at south of the Brazil–Malvinas Confluence region later being re-assimilated by the Brazil Current return flow. In situ data collected during 2 days showed that the eddy was about 150 m deep, 5.5 °C warmer and 1 practical salinity unit saltier than adjacent waters. The salt anomaly associated to the eddy was estimated as 1.37 × 10 12 kg while its heat content was 4.24 × 10 18 J. These are typical estimates for eddies present at the BMC region. Sea surface temperature (SST), chlorophyll concentration, and sea surface height anomaly time series were analyzed for the eddy's center along its trajectory path throughout its lifetime. Mean translational velocities for the eddy during its lifetime were computed from visual interpretation and by using an adaptation of the Maximum Cross-Correlation (MCC) method on AMSR-E SST images. The overall deviation between the two methods was 26%. This suggests that the MCC method has a potential to be applied in monitoring programs to automatically account for the translational velocities of eddies in the BMC region.

Spatial and temporal scales of the Brazil–Malvinas Current confluence documented by simultaneous MODIS Aqua 1.1-km resolution SST and color images

The moderate resolution imaging spectroradiometer (MODIS) on board the Aqua satellite measures visible and infrared radiation in 36 wavebands, providing simultaneous images of sea-surface temperature (SST) and chlorophyll- a (chl- a) concentration in the upper meters of the sea. For the first time, truly synoptic SST and chl- a- concentration images are available. These images are daily and of 1.1-km resolution. The strong contrasts in sea-surface temperature and surface chlorophyll- a concentration over the southwest Atlantic make satellite infrared and color images particularly appropriate tools for studying the Brazil–Malvinas (B/M) Current confluence. We examine two years (July, 2002–June, 2004) of Aqua/MODIS infrared and color images to document the precise structure of the B/M confluence simultaneously in SST and chl- a. We first compared MODIS weekly data with simultaneous independent satellite data. Spatial and temporal distributions are similar for both SST and color. Differences between MODIS and SeaWiFS (sea-viewing wide field-of-view sensor) are large in pigment-rich regions along the coast and shelf. Here, we focused on the offshore region where differences are small. For each season, exceptionally cloud-free 1.1-km resolution MODIS images showed two thermal fronts, one corresponding to the Brazil Current’s southernmost limit, the other, to the Malvinas Current’s northernmost limit. These two fronts remained quite close to each other (within 50 km) and were separated by water with an SST and chl- a concentration typical of the continental shelf waters. In spring, the water rich in chl- a from the platform is squeezed between the two currents and entrained away from the coast in between the two thermal fronts. In the frontal region, SST gradient maxima trace the contour of the chl- a-rich water. Enlargements of the frontal region and of the turbulent region downstream of the frontal collision are presented and analyzed. MODIS documents in an unprecedented way the SST and chl- a filaments as they are distorted and mixed by meso- and sub-mesoscale structures in the strain-dominated region of the B/M confluence. It is suggested that a substantial part of the chl- a local maximum in the Malvinas return flow is of continental-shelf origin.

Deep chlorophyll maximum distribution in the central Tyrrhenian Sea described by a towed undulating vehicle

The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6–7 and 26–27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.