Conductivity , Temperature And Depth Research Articles

Validation of satellite-derived tropical cyclone heat potential with in situ observations in the North Indian Ocean

Tropical cyclone heat potential (TCHP) is an important ocean parameter influencing cyclones and hurricanes. The best approach for computing TCHP is to use in situ measurements. However, since in situ data have both spatial and temporal limitations, there is a need for satellite-based estimations. One potential solution is to use sea surface height anomalies (SSHAs) from altimeter observations. However, any estimation derived from satellite measurements requires extensive regional validation. In this letter, we compare satellite-derived TCHP values with those estimated using in situ measurements of the North Indian Ocean collected during 1993–2009. All the available measurements collected from the conductivity temperature and depth (CTD) profiler, expendable CTD profiler (XCTD), bathythermograph (BT), expendable BT (XBT) and Argo floats were used to estimate in situ derived TCHP values. TCHP estimations from satellite observations and in situ measurements are well correlated, with coefficient of determination R 2 of 0.65 (0.76) and a scatter index (SI) of 0.33 (0.25) on a daily (monthly) basis for the North Indian Ocean.

2006년과 2007년 여름에 관측한 Hawaii-Chuuk 사이의 물리특성

To investigate the physical characteristics and variations of oceanic parameters in the tropical central North Pacific, oceanographic surveys were carried out in summer of 2006 and 2007. The survey periods were classified by Oceanic Nino Index as a weak El Nino in 2006 and a medium La Nina in 2007. The survey instruments were used to acquire data on CTD (Conductivity Temperature and Depth), XBT (Expendable Bathythermograph), and TSG (Thermosalinograph). The dominant temporal variation of surface temperature was diurnal. The diurnal variation in 2007, when the La Nina weather pattern was in place, was stronger than that in 2006. Surface salinity in 2006 was affected by a northwestward branch of North Equatorial Current, which implies that the El Nino affects surface properties in the North Equatorial Current region. Two salinity minimum layers existed at stations east of Chuuk in both year’s observations. The climatological vertical salinity section along 180°E shows that the two salinity minimum layers exist in 2°N~12°N region, consistent with our observations. Analysis of isopycnal lines over the salinity section implies that the upper salinity minimum layer is from intrusion of the upper part of North Pacific Intermediate Water into the lower part of South Pacific Subtropical Surface Water and the lower salinity minimum layer is from Antarctic Intermediate Water.

Seasonal and diel vertical migration of zooplankton in the High Arctic during the autumn midnight sun of 2008

The diel vertical migration (DVM) of Calanus (Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus) and Metridia longa was investigated in August 2008 at six locations to the north and northwest of Svalbard (Rijpfjorden, Ice, Marginal Ice Zone, Shelf break, Shelf and Kongsfjorden). Despite midnight sun conditions, a diel light cycle was clearly observed at all stations. We collected data on zooplankton vertical distribution using a Multi Plankton Sampler (200-μm mesh size) and an EK60 echosounder system (38, 120 and 200 kHz). These were supplemented by environmental data collected using a standard conductivity, temperature and depth (CTD) profiler. The sea ice had recently opened in Rijpfjorden, Ice and Shelf stations, and these stations exhibited phytoplankton bloom conditions with pronounced fluorescence maxima at approximately 30 m. In contrast, Kongsfjorden was more representative of autumn conditions, with the Arctic bloom having culminated 2–3 months prior to sampling. All three Calanus species were found shallower than 50 m on average at Rijpfjorden and the Ice station, while C. glacialis and C. hyperboreus were found deeper than 200 m on average at Kongsfjorden. Shallow water DVM behaviour (<50 m) was observed at Rijpfjorden and the Shelf station, especially among the C. finmarchicus CI-CIII population, which was particularly abundant at the Shelf (>5,000 individuals/m3). A bimodal depth distribution was observed among C. finmarchicus at the Shelf break station, with CI-CIII copepodites dominating at depths shallower than 100 m and CIV-adult stages dominating at depths exceeding 600 m. Statistical analyses revealed significant differences between the day and night 200-kHz data, particularly at specified depth strata (25–50 m) where backscatter intensity was higher during the day, especially in Rijpfjorden and at the Ice station. We conclude that DVM signals exist in the Arctic during late summer/autumn, when a need to feed and an abundant food source exists, and these signals are primarily due to mesozooplankton.

Towed CTD (conductivity, temperature, and depth) chain measurements in the 2010 Philippine Sea experiment.

The 2010 Philippine Sea Experiment cruise included two tows of the “towed CTD chain”, an 800‐m‐long, ship‐towed cable with 88 CTD sensor fins distributed along its length. The goal of this instrument’s use in the experiment was to obtain high‐resolution (in space and time) measurements of ocean conductivity and temperature in the upper 500–700 m of the deep‐ocean water column, in order to characterize the horizontal spatial statistics of internal waves and “spice” (density‐compensated sound‐speed fluctuations). The effects of such ocean variability upon acoustic variability in long‐range ocean acoustic propagation is an active area of current research. Despite technical difficulties with the system, measurements at 3–5 s sampling periods were obtained on one to three dozen sensors distributed over 700 m depth. The first tow was 93 km for about 39 h and the second tow was 124 km for about 30 h. These datasets will be validated and/or augmented by measurements from a Microcat CTD mounted on the bottom of the cable on each tow and a second mounted at mid‐cable during the second tow. A summary of the dataset and initial findings will be shown. [Work supported by ONR.]

Tides, the PIG, and "warm" water

The present rapid melting of the Pine Island Glacier (PIG) has been attributed to basal melting driven by the ocean. Specifically, this ocean melting is attributed to currents and tides pumping "warm" Circumpolar Deep Water (CDW) into the ice shelf cavity. To identify tidal activity in the region, an observational time series of yo-yo CTD (Conductivity, Temperature, and Depth) data collected in the PIG outflow region was analyzed. The water column in front of the PIG consisted of two primary layers, a meltwater layer exiting the ice shelf cavity over a layer of CDW. Semidiurnal tides were present in both layers, with both the strength and direction of the tides differing between the two layers. The upper layer tides were stronger and directed in and out of the cavity, while the lower layer tides were primarily directed along the front of the cavity. Energy was found to be transferred from the semidiurnal tide to other frequencies and to be reflected by the ice shelf front. These mechanisms were most prominent at the interfaces between layers and indicate potential mixing between the layers. In conclusion, tides were found to contribute to the circulation into the ice shelf cavity and also to mixing of the exiting water, which influences pumping of the CDW into the ice shelf cavity and melting of the PIG.

Estimation of submarine groundwater discharge into Geographe Bay, Bunbury, Western Australia

A study of the submarine groundwater discharge (SGD) into Geographe Bay between Bunbury and Dunsborough in the south west of Western Australia has been carried out under the CSIRO Wealth from Oceans Flagship program. The study focused on establishing a conceptual understanding of SGD and its indirect quantification using hydrogeological (hydraulic) and modeling techniques. Satellite infrared images and near shore bathymetry were used to obtain evidence of the possible geographic distribution of significant SGD. The study area forms an offshore part of the Southern Perth Basin. Past studies have shown that there is substantial groundwater flow within the Superficial, Leederville and South West Yarragadee aquifers of the Southern Perth Basin in the offshore direction. The groundwater from these aquifers must ultimately discharge offshore at the seabed into Geographe Bay in the north and the Southern Ocean in the south. Some discharge also takes place onshore via rivers and drains. The results of the study show that groundwater discharge into Geographe Bay from the Superficial Aquifer between Bunbury and Busselton is 240–284 m³/day/km of the 67 km long coastline. The offshore groundwater flow from the Leederville Aquifer along the 55 km length of the coast where the aquifer occurs is estimated at 270 m 3/d/km of the coastline. The offshore flow from the South West Yarragadee Aquifer is at the rate of 3360 m 3/d/km of the Geographe Bay coastline. The large flow rates in the South West Yarragadee Aquifer are due to substantial downward leakage from the overlying Leederville Aquifer as well as significant recharge from rainfall in the outcropping areas. The total offshore groundwater discharge to Geographe Bay from all aquifers is estimated to be around 80 million m 3/year on the basis of hydraulic assessment and the modeling results. Remotely sensed infrared images were analysed to detect evidence of any submarine groundwater discharge. The seasonal temperature contrast between the groundwater discharge at the seabed and the seawater makes it theoretically possible to detect areas of significant offshore groundwater seepage using suitable thermal images. ASTER thermal-infrared satellite images were acquired and analysed for this study. The ASTER images showed a low-temperature plume (21 °C) in the southwest of the study area near Dunsborough Fault, possibly groundwater discharge, extending in an easterly direction and being surrounded by seawater of about 23 °C. Similar cooler zones were observed along the coastline indicating groundwater discharge from the Superficial Aquifer. Following a hypothesis that former onshore coastal groundwater discharge features are likely to continue to be SGD focus areas following marine transgression, the near shore bathymetry for Geographe Bay revealed a series of ridges and troughs running sub-parallel to the present-day beach. The hillshade rendition shows a sub-parallel trough feature located about 4–5 km offshore. The bathymetric features identified offshore and the low-temperature plume as observed in the satellite images provide indicators and target areas for more detailed investigation and actual measurement of SGD fluxes, for example by CTD (Conductivity, Temperature and Depth) and SSS (side-scan sonar) probing around target bathymetric features. In the interim, this study has provided valuable information about the rate of potential groundwater seepage from the Southern Perth Basin aquifers into Geographe Bay indicating the scale of possible offshore groundwater resource availability based on SGD recovery and management.

Microbial carbon isotope fractionation to produce extraordinarily heavy methane in aging hydrothermal plumes over the southwestern Okinawa Trough

) in young to oldplume waters. We first mapped the spatial distribution of hydrothermal plumes by towing a fixed array of optical sensors(Miniature Autonomous Plume Recorders: MAPRs) above the field. We then made water column observations and samplingsusing a CTD (Conductivity, Temperature, and Depth sensors)-Carousel package with a transmissometer and Niskin-Xbottles at five locations, with distances between 0.6 and 6.1 km from the hydrothermally active center so far discovered.Vertical profiles of light transmission and chemical tracers indicated triple-layered plumes, the centers of which were atdepths of 700–800 m, ~1,050 m and ~1,200 m. The CH

Development of a New Comprehensive Ocean Atlas for Indian Ocean utilizing ARGO Data

AbstractThe World Ocean Atlas (WOA), also termed ‘Levitus Climatology’, is a global ocean climatology containing monthly, seasonal and annual means of temperature (T) and salinity (S) fields at standard ocean depths. The monthly climatology for T and S is available for standard depths up to 1000 m. The database used in the preparation of this climatology (WOA) are historical records of Conductivity, Temperature and Depth (CTD) casts and other available marine observations collected in the past. The methodology used in preparation of this WOA is objective analysis which is essentially non‐synoptic and widely scattered in the space domain. We understand that ARGO data has so far not been blended with WOA, nor has its impact for improving WOA climatology been attempted. Presently, with the wealth of marine data from ARGO profilers in the Indian Ocean, we propose a new approach to reconstruct T and S fields optimally utilizing the ARGO data. Here we develop a new model using Delaunay Tessellation with QHull algorithm delivering three‐dimensional T and S fields from a non‐uniform scattered database up to a depth of 1000 m. For gaps in a data‐sparse region, we use all available quality‐checked Ocean Station Data (OSD) and Profiling Float Data (PFL) information on T and S, in addition to the existing ARGO data. The initiative here was to replace WOA data points with realistic information from ARGO and in situ data, thereby producing a new climatology atlas. We demonstrate the robustness of our approach, and the final climatology on T and S is better compared with the existing state‐of‐the‐art WOA. The advantage of the proposed methodology is the scope of improving the ocean atlas with the addition of more ARGO data in the near future. The clustered approach in modelling enables ocean parameter retrieval in geometrically disconnected regions with an option for hot restart. We believe that the new climatology will benefit the research community immensely. Copyright © 2009 Royal Meteorological Society

Patos Lagoon outflow within the Río de la Plata plume using an airborne salinity mapper: Observing an embedded plume

Major river systems discharging into continental shelf waters frequently form buoyant coastal currents that propagate along the continental shelf in the direction of coastal trapped wave propagation (with the coast on the right/left, in the northern/southern hemisphere). The combined flow of the Uruguay and Paraná Rivers, which discharges freshwater into the Río de la Plata estuary (Lat. ∼36°S), often gives rise to a buoyant coastal current (the ‘Plata plume’) that extends northward along the continental shelf off Uruguay and Southern Brazil. Depending upon the prevailing rainfall, wind and tidal conditions, the Patos/Mirim Lagoon complex (Lat. ∼32°S) may also produce a freshwater outflow plume that expands across the inner continental shelf. Under these circumstances the Patos outflow plume can be embedded in temperature, salinity and current fields that are strongly influenced by the larger Plata plume. The purpose of this paper is to present observations of such an embedded plume structure and to determine the dynamical characteristics of the ambient and embedded plumes. We describe selected results of coincident airborne remote sensing and shipboard in-situ surveys of the salinity distribution and extent of the Plata and Patos/Mirim Lagoon plumes conducted under contrasting winter (2003) and summer (2004) conditions. The surveys were carried out in the context of a comprehensive multi-disciplinary study of the Plata plume and its response to prevailing seasonal weather conditions. The objective was to map the surface salinity distribution of the Plata plume at synoptic scales under representative winter and summer conditions. Additionally, the airborne survey included finer-scale mapping of specific features including the Río de Plata estuarine front and the Patos Lagoon plume, with the objective of determining the distribution and behavior of the plumes in the estuaries and on the continental shelf. The airborne survey was conducted with an aircraft carrying an infrared and microwave radiometer system, the Naval Research Laboratory's (NRL) Salinity, Temperature and Roughness Remote Scanner (STARRS). A series of broad-scale flights over the continental shelf off Argentina, Uruguay and Brazil were made using STARRS to determine the spatial extent of the Plata plume, and detailed mapping flights were undertaken in the vicinity of Río de la Plata Estuary and Patos/Mirim outflows to observe associated frontal features. The results of the airborne surveys were compared with shipboard hydrographic data obtained from a conductivity, temperature and depth (CTD) profiler. The combined ship and aircraft data were used to estimate parameters of dynamical classification schemes. These schemes were used to characterize the gross behavior and dynamics of the ambient Plata plume and embedded Patos plume. The Plata plume was highly asymmetric with along-shelf development towards the north and it behaved dynamically like a buoyant coastal boundary current, with an approximately geostrophic across-shelf momentum balance. The Patos plume, on the other hand, maintained its integrity as a relatively symmetric, ageostrophic, frictionally dominated plume with significant across-shelf, and modest along-shelf, development. The dynamical implications of the embedding of the smaller scale Patos plume within the larger-scale ambient Plata plume were explored, and it was concluded that the ambient plume could exert a significant dynamical influence on the behavior of the embedded plume.

Mapping of an approximate neutral density surface with Ungridded data

A neutral density surface is a logical study frame for water-mass mixing since water parcels spread along such a surface without doing work against buoyancy restoring force. Mesoscale eddies are believed to stir and subsequently mix predominantly along such surfaces. Because of the nonlinear nature of the equation of state of seawater, the process of accurately mapping a neutral density surface necessarily involves lateral computation from one conductivity, temperature and depth (CTD) cast to the next in a logical sequence. By contrast, the depth of a potential density surface on any CTD cast is found solely from the data on this cast. The lateral calculation procedure causes a significant inconvenience. In a previous paper by present author published in this journal (You, 2006), the mapping of neutral density surfaces with regularly gridded data such as Levitus data has been introduced. In this note, I present a new method to find the depth of a neutral density surface from a cast without having to specify an integration path in space. An appropriate reference point is required that is on the neutral density surface and thereafter the neutral density surface can be determined by using the CTD casts in any order. This method is only approximate and the likely errors can be estimated by plotting a scatter diagram of all the pressures and potential temperatures on the neutral density surfaces. The method assumes that the variations of potential temperature and pressure (with respect to the values at the reference point) on the neutral density surface are proportional. It is important to select the most appropriate reference point in order to approximately satisfy this assumption, and in practice this is found by inspecting the θ-p plot of data on the surface. This may require that the algorithm be used twice. When the straight lines on the θ-p plot, drawn from the reference point to other points on the neutral density surface, enclose an area that is external to the cluster of θ-p points of the neutral density surface, errors will occur, and these errors can be quantified from this diagram. Examples showing the use of the method are presented for each of the world’s main oceans.

Wind-driven monthly variations in transport and the flow field in the Faroe–Shetland Channel

The transport of water from the North Atlantic to the Nordic seas through the Faroe–Shetland Channel is analysed from a decade of conductivity, temperature and depth (CTD) and acoustic Doppler current profiler (ADCP) data. The long-term mean transport, integrated over the upper 500 m, is 3.5 } 0.1 Sv (1 Sv = 10 6 m 3 s ? 1 ), of which 2.1 Sv is barotropic flow and 1.4 Sv is baroclinic flow. Short-term variability leads to a standard deviation of ca. 2.2 Sv in 3-day averages of the ADCP-measured transport. The barotropic transport is located over the upper part of the slope region of the Shetland Shelf, but sometimes broadens over deeper water. There is a peak surface baroclinic transport above the foot of the slope, and a weak recirculation of Modified North Atlantic Water (MNAW), which enters from the north, on the Faroese side. In September, when isobars downwell on the eastern side, the strong transport (ca. 4 Sv) is barotropic and evenly distributed across the Shetland slope, and both recirculation of MNAW from the Faroe side and mesoscale activity are weak. In spring, the net transport is small (ca. 2.5 Sv), the MNAW recirculation is strong and mesoscale activity is relatively large. These seasonal variations appear to correlate with the local south-west wind stress, which may contribute to nearly half of the long-term transport in the channel.

The light transmission and seiche depth of Izmir Bay, western Turkey

Izmir Bay is one of the most polluted estuaries in the whole Mediterranean Sea. The inner part of the Bay (Inner Bay) is heavily affected by domestic and industrial discharge. As a result of these loads, strong eutrophication occurs in the Inner Bay, which is temporally anaerobic. The ecologically sensitive approach of the local authorities during the last decade has given rise to a wide variety of monitoring and research studies on this bay. On the other hand, the municipality of Izmir started to operate wastewater treatment facilities since January 2000. The Institute of Marine Sciences and Technology — Izmir (IMST) with its research vessel R/V K Piri Reis has been conducting an intensive monitoring program since 1988 and especially during the recent few years. These investigations provide an opportunity for the evaluation of the performance of the wastewater treatment plant in terms of the change in the optical properties of Izmir Bay water in a positive manner. The turbidity values measured in these monitoring studies indicate that the values have changed drastically after January 2000. Their spatial variation indicates that the values decrease from the Inner Bay towards the Aegean Sea. The turbidity (light transmission) values are measured with an automatic CTD (conductivity, temperature and depth) system during each cruise. The seiche disc depth measurement is carried out only occasionally. The accuracy of the seiche disc depth is dependent on certain daylight conditions and depends on the operator. The seiche disc depth (D s) is an important parameter to estimate primary production of organic matter (hereafter called production). A relation between light transmission (turbidity) value and seiche disc depth (D s) is found with very good agreement. The correlations are very high (approximately 0.94) with slight seasonal variation.

Effects of sill processes on the distribution of epineustonic competent larvae in a stratified system of Southern Chile

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 324:95-104 (2006) - doi:10.3354/meps324095 Effects of sill processes on the distribution of epineustonic competent larvae in a stratified system of Southern Chile Carlos Molinet1,6,7,*, Arnoldo Valle-Levinson2, Carlos A. Moreno3,7, Mario Cáceres4, Mónica Bello5, Manuel Castillo5 1Instituto de Acuicultura, Universidad Austral de Chile, Los Pinos s/n, Puerto Montt, Chile 2Department of Civil and Coastal Engineering, University of Florida, 365 Weil Hall, PO Box 116580, Gainesville, Florida 32611, USA 3Instituto de Ecología y Evolución, Universidad Austral de Chile, Casilla 567, Valdivia, Chile 4Universidad de Valparaiso, Facultad de Ciencias del Mar y Recursos Naturales, Av. Borgoño 16344, Viña del Mar, Chile 5Servicio Hidrográfico y Oceanográfico de la Armada de Chile, Errazuriz 232, Casilla 324, Valparaíso, Chile 6Centro Universitario de la Trapananda, Portales 73, Coyhaique, Chile 7Centro de Investigaciones en Ecosistemas Patagónicos, Bilbao 550, Coyhaique, Chile *Email: cmolinet@uach.cl ABSTRACT: The inlets of southern Chile are characterized by a well-defined pycnocline which, acting in concert with the biological characteristics of larvae, is believed to influence planktonic larval distribution. Here, we assessed the effects of stratified flow over a sill on the spatial abundance and distribution of epineustonic competent larvae of Concholepas concholepas. We used measurements of velocity profiles using an Acoustic Doppler Current Profiler (ADCP), intensive plankton collections combined with simultaneous conductivity, temperature and depth (CTD) profiles, monitoring of the pycnocline depth, and temperature records from moored thermistors. Evidence of Bernoulli aspiration and an intratidal transient front was observed over the sill from CTD data and an echo-sounder trace. ADCP measurements showed intensified recirculation in the residual flow over the sill. This oceanographic feature coincided with high abundances of epineustonic competent larvae of C. concholepas over the sill area. We found evidence indicating that physical mechanisms related to sill processes can influence epineustonic competent larval distribution in a stratified system. We also propose a conceptual model that brings together larval behaviour and stratified flow patterns to explain the rise of epineustonic larvae to the surface and larval aggregation over a sill. KEY WORDS: Bernoulli aspiration · Sill · Epineustonic larvae · Stratified system · Southern Chile Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 324. Online publication date: October 23, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Hydrography and geostrophic currents in the Northern Gulf of California during the 1997–1998 El Niño

Conductivity, temperature and depth (CTD) data taken during July and November 1997 and March 1998 are used to analyze the hydrographic conditions in the Northern Gulf of California during the 1997–98 El Niño. The CTD data are compared to data from other years and an anomalous high salinity, lower density water is found near the bottom, whereas a relatively fresh surface layer is found on the eastern side of the gulf during July. The relatively fresh surface water is attributed to advection of tropical waters from the Pacific Ocean. During November and March, positive surface temperature anomalies are identified. Geostrophic currents are calculated across an entire cross section of the gulf passing through the northern tip of Angel de la Guarda Island using either salt or mass conservation as constraints. The most salient feature of the geostrophic currents is the existence of relatively intense bottom currents. The bottom current on the eastern side of the island is southeastward, toward the mouth of the gulf, during July, whereas it is toward the head of the gulf on the western side of the island. This pattern is inverted during November and March and, in all cases, suggests a near-bottom circulation between both basins separated by the island. The near-bottom current toward the head of the gulf on the eastern side of the island appears to be a permanent feature associated with the exchange of the northern gulf. Therefore, the high near-bottom salinities during July, coupled with a current toward the mouth of the gulf, are attributed to an anomalous condition created by the El Niño event. This condition is consistent with a subsidence of Gulf of California waters, flowing toward the mouth. Fluxes of salt and heat estimated from geostrophic currents are compared to seasonal estimates. The July heat flux is about three times greater than the seasonal value, and there appears to be an overall phase shift with respect to the seasonal cycle.

Calculation of fine-scale sound-field structure based on towed CTD (conductivity, temperature, and depth) chain measurements

In July 2002, an experiment was conducted off the coast of southern California in which the two-dimensional temperature and salinity field was measured directly using a towed CTD chain. The sensor spacing was smaller (2 to 8 m) near the surface (above 30 m) in order to better resolve the mixed layer and thermocline; the depth of the lowest sensor was about 150 m. The path of each tow was back and forth across the same section of ocean such that ocean dynamic features observed in the CTD data were recorded in expanded and compressed states depending on the ship’s heading. The range of each run was a few kilometers, with data taken in 1-s increments. This yielded a high-resolution field suitable for analyzing the propagation behavior of high frequencies. Using the fine-scale measurements of the sound-speed field and an acoustic propagation model based on an FFT-realized parabolic equation, the sound field was calculated reflecting the observed ocean dynamic features. Modeling of scintillation in acoustic intensity will be discussed in the context of spice theory. [Work supported by ONR Code 321US.]

Determination of dynamic heights in the Bay of Bengal from XBT profiles and climatological salinities

Dynamic height (DH) computations are necessary for the estimation of geostrophic currents, heat transport studies, identification of eddies and to validate the altimeter sea surface height (SSH) observations. To compute DHs we need the temperature and salinity profiles to a reasonable deeper level. But, temperature profiles alone, such as from XBT (expendable bathy thermograph), are more numerous than combined temperature and salinity measurements from CTD (conductivity, temperature and depth). To use these voluminous temperature measurements from XBT observations in the computation of DHs, temperature/salinity relations were developed in many oceanic regions. Since such an exercise cannot be carried out in the Bay of Bengal due to the absence of adequate CTD measurements, we have proposed a method of utilizing XBT measurements and climatological (Levitus and Boyer, 1994) salinities to compute the DHs. The approach is demonstrated by replacing the CTD salinities with the climatological salinities. The relative errors compared to the DH signals are 3.8%, 2.7% and 2.6% for 200, 700 and 1000 dbar levels, respectively. The DHs relative to 700 dbar computed using the XBT temperature and climatological salinity profiles are compared with the SSH observations from TOPEX altimeter. The standard deviation of the difference between the DHs computed after converting to geometrical units and SSH is 7.3 cm.

Simulation and analysis on seasonal variability of average salinity in the Yellow Sea

The CTD (conductivity, temperature and depth) data collected by six China-Korea joint cruises during 1996–1998 and the climatological data suggest that the seasonal variability of average salinity in the Yellow Sea (Sa) presents a general sinusoid pattern. To study the mechanism of the variability, annual cycles ofSa were simulated and a theoretical analysis based on the governing equations was reported.

Dynamics and water mass structure of a summertime anticyclonic eddy in Funka Bay, Hokkaido, Japan

The hydrography and flow structure of an anticyclonic eddy are investigated synoptically using conductivity, temperature and depth (CTD) and Acoustic Doppler Current Profiler (ADCP) data for Funka Bay on June 17 and July 23, 1997. In June, the anticyclonic eddy was characterized by a deep concave structure of isopycnal surfaces, with elliptical horizontal shape. The tangential speed of the eddy at 10 m depth approached a maximum of 30 cm s −1 at a radius of about 10 km. In July, the eddy was characterized by a sharp pycnocline with two density fronts around the outer edge of the eddy at a depth of 10 m. The horizontal shape of the eddy became circular, and the maximum tangential speed at 10 m depth decreased to 25 cm s −1 at a radius of about 15 km. The core of the eddy rotated as a rigid body through one cycle approximately once every 2.3 days in June, and every 4.8 days in July. Analysis of the tangential currents at 10 m depth using the gradient flow relationship revealed that the eddy was hydrodynamically balanced between three forces: Coriolis force, centrifugal force and a force due to the horizontal pressure gradient. The vertical and horizontal scales of the eddy changed dramatically between June and July, with the vertical scale of the eddy becoming shallower as the deep concave structure of the isopycnal surfaces was destroyed due to the intrusion of water originating from Tsugaru warm water (TW). The horizontal scale of the eddy also decreased from June to July, related to the formation of two density fronts arising due to coastal upwelling associated with south-southeasterly winds and due to contact of the eddy with water originating from TW in the upper layer. The coastal upwelling not only changed the horizontal structure of the eddy, but also transported nutrients to the surface layers from deeper layers. These nutrients would promote primary production in summer in Funka Bay. The collection of scallop larvae by aquacultural netting at fixed coastal sites would therefore be strongly affected by the eddy, suggesting that the eddy plays an important role in the ecosystem of Funka Bay.

Tidally-induced clouds of suspended sediment connected to shallow-water coral reefs

The Bay of Banten, West Java, Indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions. The sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration (SSC) around the reefs. Arrays of in situ calibrated optical backscatter (OBS) sensors were deployed across the reef slopes. Far field conditions were simultaneously monitored using an acoustic Doppler current profiler (ADCP) and a conductivity temperature and depth (CTD) probe, equipped with an OBS sensor. In addition, hydrographic surveys were conducted using the ADCP attached to a small fishing boat, navigating transects perpendicular to the reef islands. The direct influence of river plumes was found to be insignificant. Waves act only in the uppermost few meters of the reef slopes, where coral growth is most abundant and little sediment is available for resuspension. Tidal currents are the primary cause of high turbidity, which was inferred from peaks in the diurnal and semidiurnal frequency bands of SSC spectra, and the large depths where the turbidity variation sometimes initiates. The entrained sediment disperses upward across the reef slopes, which is likely due to a secondary current associated with bending of the flow along the curved, hydraulically rough reef slopes, in weakly stratified ambient waters. Changes in sediment availability, variable critical shear stresses for erosion and deposition, and the formation and evanescence of island wakes may explain the high variability of SSC at the reef slopes.

SURFACE FEATURES OF THE CIRCULATION IN FJORDS OF SOUTHERN CHILE OBSERVED IN ERS AND LANDSAT IMAGES

Surface features of the hydrodynamics at the mouth of Aysen Fjord, in the Chilean Inland Sea, were described using Landsat and ERS-SAR images in combination with field data. A set of seventeen radar images from ERS, along with one Landsat (ETM) were analyzed to study the surface features observed in this region, where fresh water input is an important contributor to the dynamics of the estuarine system. Field data were provided by current measurements obtained with an Acoustic Doppler Current Profiler (ADCP) mounted in a catamaran looking downward, which was towed from a boat during two semidiurnal cycles to obtain repetitions over two transverse transects. There were also density measurements obtained from CTD (Conductivity, Temperature and Depth) vertical profiles in the water column and from a surface termosalinograph (Conductivity, Temperature) mounted onboard of a research vessel. The results of this campaign in Aysen Fjord were associated to the surface features observed in satellite images. The results show the main features of the circulation at the mouth of this fjord and other phenomena of interest for physical oceanography. Noteworthy is a frontal structure suggested on both types of images. This feature is partially supported by ADCP measurements and strongly suggested by density measurements. Packages of internal waves in Costa Channel are also suggested in radar images, while the distribution of the fresh water plume is supported by the Landsat image. Satellite images provided valuable guidance to focus the research in a selected area and phenomena.