Surface Current Patterns Research Articles

A Compact Tunable Internal Antenna for Personal Communication Handsets

This letter presents a compact tunable internal planar inverted-F antenna (PIFA) for personal communication handset applications. The antenna operates at following frequency bands: DCS, PCS, UMTS, WiBro, WiMax and/or WiBro phase 3, and WLAN. A single varactor diode is attached to the antenna in a proper location between the main patch and supplemental patch in order to get tuning over the wide frequency range around 2 GHz. The antenna was designed and optimized by using CST microwave studio program. Measured return losses (S11) and radiation patterns of the antenna were carried on Anritsu 37377C Vector Network Analyzer and in standard anechoic chamber room. The surface current distributions, the co-polarization and cross-polarization patterns of the antenna are given to demonstrate the antenna's performance.

Frequency notched wide slot antenna for UWB/2.4 GHz WLAN applications

A compact frequency notched microstrip slot antenna for ultra-wideband (UWB) /2.4 GHz-band wireless local area network (WLAN) applications is proposed. The antenna is similar to a conventional microstrip slot antenna; however, by introducing a cross wide slot and a meandered-slotted stub, both compact size and frequency notched function can be achieved. It has been studied both numerically and experimentally for its impedance bandwidth, surface current distribution, radiation patterns, and gain. As will be seen, an operation bandwidth of over 4.6:1 ranging from 2.39 to 11.25 GHz for return loss lower than -10 dB having a frequency notched band ranging from 4.75 to 5.85 GHz has been achieved, and good radiation performance over the entire frequency range has also been achieved.

Mesoscale eddies, surface circulation and the scale of habitat selection by immature loggerhead sea turtles

Here we tested whether the dispersal of loggerhead sea turtles in the western Mediterranean was affected by the pattern of surface currents and whether temporary mesoscale eddies were favoured habitats by comparing the distribution of ten satellite-tracked turtles (average straight carapace length = 46.3 cm; range: 37.1–61.1 cm) with satellite images indicative of the position of mesoscale eddies and the Algerian current. The tracking period averaged 120.9 ± 67.0 SD days. The comparison of turtle tracks with satellite images revealed that only 9.5% of the fixes were associated with mesoscale eddies or the Algerian current. However, 28.3% (range: 0–60.0%) of the maximum longitudinal displacement of each turtle occurred while swimming in the Algerian current. Furthermore, accelerated eastward dispersal with the Algerian current was the most likely reason why turtles did not penetrate deep into the Alboran Sea. Conversely, mesoscale eddies were not involved in any net latitudinal or longitudinal displacement of the turtles. Track analysis revealed that only a few turtles were involved in fine habitat search, as the speed of travel and the cosine of the turning angle seldom correlated once the drift associated with the Algerian current and with mesoscale eddies had been removed from the analysis; only the turtles approaching the limits of the Algerian basin modified their swimming behaviour, thus indicating habitat selection. These observations and the results of the simulation experiments revealed that turtle dispersal within the western Mediterranean was a combination of: (1) passive dispersal within a region limited by physical barriers (the Balearic Archipelago, Sardinia, Corsica, and Sicily) and influenced by a strong current (the Algerian current) and (2) fidelity to regions filled with recent Atlantic water. However, turtles fail to recognise and remain in small, discrete mesoscale eddies, thus suggesting that habitat selection in these turtles appears to occur at the scale of hundreds rather than tens of kilometres.

Genetic structuring of immature loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea reflects water circulation patterns

The analysis of mitochondrial DNA in loggerhead sea turtles (Caretta caretta) from eight foraging grounds in the Mediterranean and the adjoining Atlantic revealed deep genetic structuring within the western Mediterranean. As a consequence, the foraging grounds off the North-African coast and the Gimnesies Islands are shown to be inhabited mainly by turtles of the Atlantic stocks, whereas the foraging grounds off the European shore of the western Mediterranean are shown to be inhabited mainly by turtles from the eastern Mediterranean rookeries. This structuring is explained by the pattern of sea surface currents and water masses and suggests that immature loggerhead sea turtles entering the western Mediterranean from the Atlantic and the eastern Mediterranean remain linked to particular water masses, with a limited exchange of turtles between water masses. As the north of the western Mediterranean comprises mostly individuals from the highly endangered eastern Mediterranean rookeries, conservation plans should make it a priority to reduce the mortality caused by incidental by-catch in these areas.

Population genetics of Zostera noltii along the west Iberian coast: consequences of small population size, habitat discontinuity and near-shore currents

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 290:89-96 (2005) - doi:10.3354/meps290089 Population genetics of Zostera noltii along the west Iberian coast: consequences of small population size, habitat discontinuity and near-shore currents Onno E. Diekmann1, James A. Coyer2, Joao Ferreira1, Jeanine L. Olsen2,Wytze T. Stam2, Gareth A. Pearson1, Ester A. Serrão1,* 1CCMAR – CIMAR Laboratório Associado, Universidade do Algarve, FCMA, Gambelas, 8005-139 Faro, Portugal2University of Groningen, Biological Center, PO Box 14, 9750 AA Haren, The Netherlands *Corresponding author. Email: eserrao@ualg.pt ABSTRACT: The effects of oceanographic patterns on marine genetic biodiversity along the SW Iberian Peninsula are poorly understood. We addressed the question of whether gene flow in this region depends solely on geographic distance between isolated patches of suitable habitat or if there are superimposed effects correlated with other factors such as current patterns. Zostera noltii, the dwarf eelgrass, is the keystone habitat-structuring seagrass species on intertidal mudflats along the Iberian west coast. We used 9 microsatellite loci to analyze population genetic diversity and differentiation for all existing 8 populations from NW Spain (Ria de Vigo) to SW Spain (Puerto Real, Cadiz). Populations are highly genetically differentiated as shown by high significant FST,Wright’s fixation index, (0.08 to 0.26) values. A neighbor-joining tree based on Reynold’s distances computed from allele frequencies revealed a split between northern and southern populations (bootstrap support of 84%). This pattern of differentiation can be explained by (1) ocean surface current patterns present during Z. noltii’s reproductive season which cause a dispersal barrier between the northern and southern populations of this region, (2) habitat isolation, due to large geographic distances between suitable habitats, preventing frequent gene flow, and (3) small effective population sizes, causing high drift and thus faster differentiation rates. KEY WORDS: Phylogeography · Dwarf eelgrass · Seagrass conservation · Iberian Peninsula biogeography · Portuguese coast Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 290. Online publication date: April 13, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Universal Early-Time Response in High-Contrast Electromagnetic Scattering

The time-domain response of highly conducting targets following a rapidly terminated electromagnetic pulse displays three distinct regimes: early, intermediate, and late time. The intermediate and late times are characterized by a superposition of exponentially decaying eigenmodes. At early time an ever increasing number of rapidly decaying modes contribute, with the result that the scattered electric field displays a universal t(-1/2) power law which emerges from the diffusive decay of a pattern of surface currents induced by the pulse. The power law amplitude reflects the surface geometry of the target, a property that may prove useful in buried target classification in geophysical remote sensing applications.

Magnetic field and currents in HTSC films

Abstract Magnetic field measurements above type-II superconductor films in a remanent magnetization state have been used to determine two dimensional surface current distributions. Using the Biot-Savart law for the surface current density, integral equations (of 2-D convolution type) for two components of current have been obtained. These equations have been solved by employing Tikhonov's method of generalized discrepancy, and the surface current pattern in superconductors as well as the magnetic field distribution on the film surface have been obtained. Current peculiarities related to various kinds of inhomogeneities, specific character of the film form, and a laser pulse effect have been observed. In particular, it was discovered that a laser pulse can signficantly redistribute the film currents without changing the total number of current vortices in the film.

Sleeve monopole on a circular ground‐plane

AbstractThis paper presents a modal‐expansion analysis of a sleeve monopole antenna on a finite ground‐plane. Two perfectly conducting plates (one above the monopole and the other under the ground‐plane) are introduced to confine the modeling region and to facilitate the modal‐expansion analysis. The resulting guided‐wave structure is then divided into a number of regions and the electromagnetic field components in each region are expanded into the summation of its modal functions. The surface current distribution on the monopole and the antenna's input impedance and radiation pattern are obtained by finding the expansion coefficients through matching the tangential field components across the regional interfaces. Calculated results by the modal‐expansion method agree well with measured results for the return loss of a sleeve monopole fed through a circular ground‐plane by a coaxial probe. Numerical results for the surface current distribution, input impedance, and radiation pattern of a sleeve monopole on a circular ground plane are presented and discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Nearshore surface current patterns in the Tsitsikamma National Park, South Africa

The pattern of surface currents in the Tsitsikamma National Park, South Africa, was studied with holey-sock drogues released in batches of up to four at a time, from 1996 and 1998. Drogues were left to drift for either 6 or 24 h, while recording position and time. The majority of drogue movements were longshore, either eastward or westward; they usually travelled with similar direction and velocity. In most instances, westward movements were slightly offshore and were sometimes associated with a rise in the thermocline. Eastward movements were, on average, slightly slower, with an onshore component, sometimes associated with a lowering of the thermocline. The remaining trials showed some variability between drogues and were characterized by reduced velocity and unstable direction, indicating either the presence of horizontal turbulence or a current reversal. Current and wind were poorly correlated. Current directions were sustained for at least four days, indicating that short-lived ichthyoplankton, originating in the 70-km park, may be dispersed beyond its boundaries.

Effects of tidal current phase at the junction of two straits

Estuaries typically have a monotonic increase in salinity from freshwater at the head of the estuary to ocean water at the mouth, creating a consistent direction for the longitudinal baroclinic pressure gradient. However, Mare Island Strait in San Francisco Bay has a local salinity minimum created by the phasing of the currents at the junction of Mare Island and Carquinez Straits. The salinity minimum creates converging baroclinic pressure gradients in Mare Island Strait. Equipment was deployed at four stations in the straits for 6 months from September 1997 to March 1998 to measure tidal variability of velocity, conductivity, temperature, depth, and suspended sediment concentration. Analysis of the measured time series shows that on a tidal time scale in Mare Island Strait, the landward and seaward baroclinic pressure gradients in the local salinity minimum interact with the barotropic gradient, creating regions of enhanced shear in the water column during the flood and reduced shear during the ebb. On a tidally averaged time scale, baroclinic pressure gradients converge on the tidally averaged salinity minimum and drive a converging near-bed and diverging surface current circulation pattern, forming a “baroclinic convergence zone” in Mare Island Strait. Historically large sedimentation rates in this area are attributed to the convergence zone.

Late Pliocene fossils of Ecuador and their role in the development of the Panamic bioprovince after the rising of Central American Isthmus

Studies carried on in the last several years allow us to date the Canoa Formation as Late Pliocene. The rich paleontological record (foraminifers, mollusks, and otoliths) allowed us to outline a first articulate picture of the biogeographic relationships in the tropical eastern Pacific during the Plio-Pleistocene. The mollusk fauna shows a Panamic connotation, as the majority (88.7%) of the extant species are present between the Gulf of California and the coasts of Ecuador or northern Peru. Benthic foraminifers assemblages indicate a temperate character with a certain affinity with the Mexican Pacific microfauna. More than 7000 otoliths have been found in the Canoa Formation that are attributed to 105 taxa of 46 fish families. Only 65% of the fossil association is living today along the Ecuadorian coasts, while the association as a whole shows closer relationships with the extant Californian fish community (about 80%). In particular, a conspicuous group of fishes (15 taxa) today spread in the boreal East Pacific (from Oregonian to Californian Province or limited only to the Californian area) has been recorded in the Canoa Formation. We named these taxa "Californian guests." After the rising of the Central American Isthmus, climatic variations may have caused changes in the pattern of surface currents and (or) activated coastal upwelling cells, supporting the diffusion of a part of the boreal biota toward more southern areas. At the present state of knowledge, both proximal causes seem to be compatible with the data presented.

Using Remote Sensing to Reassess the Mass Mortality of Diadema antillarum 1983–1984

Abstract: The 1983–1984 mass mortality of the sea urchin Diadema antillarum remains one of the most severe die‐offs ever recorded in the Caribbean. Before 1983, the herbivore D. antillarum was pervasive on coral reefs in the region. Nine months after first detection of the mass mortality, 95% of the urchins had perished, and algal cover of coral increased between 100% and 250%. A water‐borne pathogen was hypothesized as the causative agent, but it was never isolated. To date, surface current patterns have been used exclusively to explain both the cause and the distribution patterns of the mortality event. Using archived satellite images, we re‐examined the water‐borne pathogen hypothesis and investigated whether other mechanisms could also account for the dissemination pattern in some areas. In addition, archived satellite images were utilized to detect changes in coral reef reflectance. For infections in the Gulf of Mexico and Bermuda, satellite images confirm that surface currents are likely responsible for the distribution of the pathogen. For infections in the eastern Caribbean (Curacao, U.S. Virgin Islands, Barbados), however, another mechanism, possibly ballast water exchange, must be considered because the surface current and infection patterns do not coincide. Changes in coral reflectance were detectable from Landsat thermatic mapping data before and after the mass mortality and correspond to the change in algal cover. Results from our study demonstrate the potential of satellite images for use in determining connectivity between regions of the Caribbean and in detecting changes in coral reef cover.

Winter distribution, ontogenetic migration, and rates of egg production of Calanus finmarchicus southwest of Iceland

The winter distribution, seasonal vertical migration, and reproduction of Calanus finmarchicus in relation to water masses and chlorophyll a were investigated southwest of Iceland between November 1996 and June 1997 as part of the TASC programme. During winter (November/December, January/February), overwintering C. finmarchicus were generally located beyond the shelf (5000-30 000 individuals m −2 ); by contrast, overwintering animals were usually scarce on the banks ( 2000 m) at temperatures of ∼3-8°C, whereas in the Irminger Basin the distribution was mainly ∼200-1800 m in waters of ∼3-6°C. During winter, most of the stock was present as C5 (84-86%), with a smaller proportion as C4 (12-14%) and females (1-2%). Overwintering animals resided mainly in water of Atlantic origin, but some animals were found in Labrador Sea Water and Iceland-Scotland Ridge Overflow Water. Ascent to upper layers probably took place mainly during March and April, and continued until May. On the basis of the horizontal and vertical distribution of overwintering animals and the general surface current pattern, the banks seem to be repopulated mainly from the south. By April the spring growth of the phytoplankton was about to begin on the banks, and C. finmarchicus had started to lay eggs (0-7 eggs female −1 d −1 ). Maximum individual rates of egg production (2-46 eggs female −1 d −1 ) were observed in June, at the time of maximum phytoplankton biomass accumulation. During April, the population's average rate of egg production on the banks (∼1000 eggs m −2 d −1 ) was rather similar to that in the open ocean (∼600 eggs m −2 d −1 ), whereas during June it was significantly higher in the oceanic region (∼16 000 eggs m −2 d −1 ) than in shelf waters (∼900 eggs m −2 d −1 ), mainly because of the greater number of spawning females in the oceanic environment.

Identity and Dispersal of Aleurites erratica (Euphorbiaceae), a Pacific Drift Seed Synonymised with Omphalea papuana

Summary. The external morphology of seeds of Aleurites erratica 0. Deg., I. Deg. & Hummel, known only from beach drift in the SW and central Pacific, was compared with that of members of the Aleuritinae (Aleurites, Vernicia, Reutealis) and Omphalea in this region (all Euphorbiaceae), and found to match Omphalea papuana Pax & K. Hoffm. from Papuasia and NE Australia. Reversals of the usual pattern of easterly oceanic surface currents in the South Pacific at these latitudes and strong westerly winds are associated with El Nifio episodes and could explain how drift seeds from the SW Pacific reached Kanton Atoll, Phoenix Group, Kiribati, from where A. erratica was first described.

Variation of the bathymetric distribution patterns of the macrobenthic fauna on the continental shelf off Jalisco and Colima, Mexico

The abundance, in terms of number of individuals and biomass, of the invertebrate communities in one sector of the soft-bottom continental shelf off Jalisco and Colima (Mexico) was analyzed. The cruises were carried out during three hydroclimatic seasons, as defined by the surface current patterns. Trawl samples were taken from seven sites along the coastline at four bathymetric levels (20, 40, 60 and 80 m), Abundance in the different bathymetric strata was significantly different, but the overall abundance did not vary significantly between seasons. Two bathymetric distribution patterns were found: the first, during the cruises DEM 1 and DEM II, with warm water, presents the greatest abundance at 60 m; the second, during DEM III, with cold water, a low leve1 of dissolved oxygen and the thermocline close to the surface, presents the greatest abundance at 20 m (biomass) and 40 m (number of individuals). The temperature fluctuation in the depth of maximum abundance during the three cruises was 19-2lºC, which suggests a narrow range of thermal preferente in the demersal invertebrate community.

Connectivity and management of caribbean coral reefs

Surface current patterns were used to map dispersal routes of pelagic larvae from 18 coral reef sites in the Caribbean. The sites varied, both as sources and recipients of larvae, by an order of magnitude. It is likely that sites supplied copiously from "upstream" reef areas will be more resilient to recruitment overfishing, less susceptible to species loss, and less reliant on local management than places with little upstream reef. The mapping of connectivity patterns will enable the identification of beneficial management partnerships among nations and the design of networks of interdependent reserves.

Climatology and interannual variability simulated by the ARPEGE-OPA coupled model

A 10-year simulation with a coupled ocean-atmosphere general circulation model (CGCM) is presented. The model consists of the climate version of the Meteo-France global forecasting model, ARPEGE, coupled to the LODYC oceanic model, OPA, by the CERFACS coupling package OASIS. The oceanic component is dynamically active over the tropical Pacific, while climatological time-dependent sea surface temperatures (SSTs) are prescribed outside of the Pacific domain. The coupled model shows little drift and exhibits a very regular seasonal cycle. The climatological mean state and seasonal cycle are well simulated by the coupled model. In particular, the oceanic surface current pattern is accurately depicted and the location and intensity of the Equatorial Undercurrent (EUC) are in good agreement with available data. The seasonal cycle of equatorial SSTs captures quite realistically the annual harmonic. Some deficiencies remain including a weak zonal equatorial SST gradient, underestimated wind stress over the Pacific equatorial band and an additional inter-tropical convergence zone (ITCZ) south of the equator in northern winter and spring. Weak interannual variability is present in the equatorial SST signal with a maximum amplitude of 0.5°C.

General Circulation of the Northern Adriatic Sea: Results of Long-term Measurements

Residual sea currents of the northern Adriatic were analysed in the sense of the general (global) circulation, over a period of 42 months (in one main and two control stations). At the end of the summer season and the beginning of autumn (in the so-called ‘inversion period’) residual surface (6m) sea currents at the main station showed characteristic seasonal behaviour: a change of direction from the north (NW, N, NE) to the south-east (SE). The sequence with SE directions lasted about 1·5 months. After that, directions changed again to the NW (or N). The direction of bottom residual currents (37m) in this inversion period had the same pattern as the surface ones. This behaviour of the currents can be associated with the change of the cyclonic gyre into the anticyclonic. In all other periods at the main station the surface residual sea currents have predominant north directions. Bottom residual currents mainly followed the pattern of surface currents for all stations and periods, except during the periods from January to June 1990 and 1992, when they were of opposite direction at station B.

Biogeographical analysis of Late Silurian brachiopod faunas, chiefly from Asia and Australia

Shallow water benthic marine invertebrates (such as brachiopods from Benthic Assemblages [BA] 1–3) have usually played a much more important role than deeper ones (BA 4–5 or even deeper) in evaluating biogeographical provincialism in geological history. The Silurian brachiopod Retziella Fauna, characterized by the common presence of Retziella in association with various provincial taxa and many common North Silurian Realm genera, is known from southwest Tienshan, North China, South China, North Vietnam, and East Australia. It is possibly also present in North Korea, the central Pamirs, Afghanistan, and New Zealand. The coeval Tuvaella Fauna occurs only in the southern marginal belt of the Siberian Plate. Synecologically, both faunas inhabited a normal, shallow-water, level-bottom environment, usually with a low-diversity community (commonly 3–8 genera); assignment to BA 2–3 is indicated. Their mutual exclusiveness is of biogeographical significance: subdivisions of the Uralian-Cordilleran Region can be based on them, with the Tuvaella Fauna being included in a redefined Mongolo-Okhotsk Province. A Sino-Australian Province is established and defined herein for the area occupied by the Retziella Fauna during the Ludlow-Pridoli and probably the Wenlock. Two subdivisions of the province can be recognized, a Sino-Central-Asian Subprovince and an Australian Subprovince, based on different endemic brachiopods and separate geographical positions. The presence of a number of more cosmopolitan genera in both the tropical-subtropical Sino-Australian and subtropical-temperate Mongolo-Okhotsk Provinces during the Late Silurian testifies to oceanic surface current circulation patterns adequate for the distribution of planktic larvae capable of long-distance dispersal while maintaining reproductive communication. This contrasts with the dispersal potential of endemic components of the newly defined Silurian biogeographical units. □ Late Silurian, Brachiopoda, Retziella, Fauna, Tuvaella Fauna, Synecology, Biogeography, Asia, Australia

Studies of sea surface temperatures in selected northern Norwegian fjords using Landsat TM data

Remote sensing is evaluated as a tool for studying oceanographic phenomena. Data from the infrared channel of Thematic Mapper onboard Landsat 5 were used to map the spatial distribution of sea surface temperatures in selected fjords in northern Norway. Sea surface temperature charts provided clear indications of surface current patterns, upwellings, convergences, etc. The complex pattern of currents found in fjords is, to varying degrees, affected by tides and fresh water run-off, as well as by hydrographic, meteorological and topographical conditions. In northern Norway the surface circulation is strongly influenced by inland cold air flows during prolonged periods of cold weather. This study demonstrates that remotely sensed data can be used as an important supplement to traditional hydrographical and meteorological observations in order to understand the distribution of temperatures and circulation patterns in the surface layers of fjords and coastal waters.