1,720,993 research outputs found
Aspects of the circulation in the Rockall Trough
Full text linkAn investigation is made of the circulation and structure of the water masses in the Rockall Trough in spring, combining the results of a recent synoptic survey (May 1998) with those from a high-resolution ocean circulation model. In the near-surface layer, saline flows are carried northwards by a "Shelf Edge Current" around the eastern slopes, possibly with some branching in the northern Trough. Fresher waters from the west inflow between 52 and 538N and partially mix with these saline flows in the southern Trough, so that waters of intermediate salinity are also swept northwards. In the southern approaches to the Trough, Labrador Sea Water (LSW) also flows strongly in from the west between 52 and 538N, and while much of this turns south, a proportion penetrates north to join a cyclonic gyre in the Trough extending to 56.58N. The northwestern limb of this gyre is fed by, and mixes with, more saline waters which result from overflows across the Wyville–Thomson Ridge. Furthermore, salinity and CFC data suggest episodic inflow of LSW into the central Trough. The circulation of the North East Atlantic Deep Water in the Trough follows a cyclonic pattern similar to, and lying below, that of the LSW. The Wyville–Thomson Ridge overflows in the model extend to higher densities than in the survey, are topographically steered southwestward down the Feni Ridge system, and eventually join a deep cyclonic circulation in the North East Atlantic basin. Overall, the model and the observations are in good agreement, particularly in the central Rockall Trough, and this has allowed conclusions to be drawn which are significantly more robust than those which would result from either the survey or the model alone. In particular, we have been able to infer cyclonic circulation pathways for the intermediate and deeper waters in the Rockall Trough for (we believe) the first time. The study has also contributed to an ongoing community effort to assess the realism of, and improve, our current generation of ocean circulation models
RRS Charles Darwin Cruise 141, 01 Jun-11 Jul 2002. Satellite Calibration and Interior Physics of the Indian Ocean: SCIPIO
Full text linkRRS Charles Darwin Cruise 141, SCIPIO (Satellite Calibration and Interior Physics of the Indian Ocean) provided a multidisciplinary survey of the Mascarene Ridge system in the western Indian Ocean. The principal objectives were to (a) study the flow of water masses through the Ridge system, together with their decadal-timescale variability, (b) assess the energy fluxes and mixing arising from internal waves, (c) collect in situ data for the calibration of sea-surface temperature and ocean colour sensors on the ENVISAT satellite, (d) investigate the biogeochemical properties of the water masses, and (e) measure the heat fluxes and winds, and the airflow disturbance around the ship. The survey comprised three sections parallel with the Ridge near 64°, 60° and 57° E, joined by two other sections at 8° and 20°S. The sections comprised CTD, LADCP, and biogeochemistry (nutrients, phytoplankton, zooplankton, biogenic gases, CFC tracers and light levels) stations to full ocean depth, at typical spacings of about 60-80 nm. At several of these the CTD and LADCP were cycled continuously for a semidiurnal tidal cycle to study the internal waves, and the smaller 12-bottle CTD frame was used throughout (usually with 6 bottles) in order to reduce mixing effects from the trailing wake. Underway measurements were made with the shipboard ADCP, TSG, radiosondes, XBTs, and of surface meteorology, skin surface temperature, and zooplankton. The ship's EM12 swath bathymetry system was operated continuously, and used to study certain key areas in detail. In addition, MMP (a cycling CTD) and bottom-mounted ADCP moorings were successfully laid and recovered near 8°S, 60°E, and a first deployment of the ARGODOT turbulence probe was made near 20°S, 57.5°E
An introduction to the RDI Acoustic Doppler Current Profiler as used on "Challenger" Cruise 15
No full textARE/IOSDL Contract 'Studies in the upper ocean'. Summary report for April 1985 - April 1990: Phases I and II
No full textRemote-sensing evidence for the local generation of internal soliton packets in the central Bay of Biscay
No full textLarge-amplitude internal solitary waves (or “solitons”) occurring in packets near the shelf break in the Bay of Biscay are well-documented and understood. The presence of similar features has now also been reported in the central Bay, ?150 km from the nearest shelf break topography. The present paper analyses available remote-sensing synthetic aperture radar (SAR) data from the ERS satellites in this region. By doing so, we are able to provide convincing support for the hypothesis that these waves, instead of having travelled along the thermocline from the shelf break, are instead generated locally in the central Bay by the surfacing of a beam of internal tidal energy originating from the shelf break. This reinforces the results of a previous independent study, while at the same time providing a much more extensive investigation than was then possible. We have also exploited the large swath width (100 km) and high spatial resolution (100 m×100 m) of the SAR to examine for the first time the full surface structure of the internal waves in the central Bay, which are found to have a mean wavelength of 1.35 km, and a mean along-crest “coherence” length of 21.55 km
Internal solitary waves in the Mozambique Channel: Observations and interpretation
Full text linkThis paper presents new results showing that the Sofala shelf in the Mozambique Channel (20°S, 36°E) is a previously unknown “hot spot” for the generation of internal tides and internal waves. We investigate available Envisat advanced synthetic aperture radar imagery of the region, which is capable of showing the surface signatures of the internal waves. This is complemented by modeling of the ray pathways of internal tidal energy propagation, and of the P. G. Baines (1982) barotropic body force, which drives the generation of internal tides near the shelf break. The hot spot region is localized between 20° and 21°S because of the particular nature of the bathymetry there. Farther north and south, the forcing is reduced and insufficient to generate internal solitary waves in the synthetic aperture radar images. The analysis reveals two distinct types of internal wave trains that are observed traveling oceanward away from the shelf break, and we suggest that these result from direct generation at the shelf break and from “local” generation at about 80 km from the shelf break, respectively, because of the surfacing of internal tidal rays at the thermocline. Finally, we have investigated seasonal differences in the wave patterns, which penetrate more extensively into the channel during the southern summer and appear slightly farther to the south during the southern winter. We also conclude that the local generation process is more likely to occur during the winter when the stratification is reduced. <br/
On the role of SAR for observing 'local generation' of internal solitary waves off the Iberian Peninsula
No full textInternal tides are well known to result from the interaction of the surface tide with steep sea-floor or shelf-break topography. Large-amplitude internal solitary waves (ISWs) have been observed occurring in packets in open ocean areas well away from such pronounced topography. The Bay of Biscay is a region where these waves could be generated “locally” by the reflection or scattering of an internal tidal beam from the near-surface thermocline. In this paper we investigate available ENVISAT ASAR and ERS SAR imagery to study the generation of ISWs in the southern Bay of Biscay (43–45°N, 7–10°W) and off the southwest Iberian Peninsula (37–39°N, 8.5–10.5°W). In the southern Bay of Biscay, image analyses have shown the presence of packets of ISWs propagating towards the north-northwest (in addition to the previously observed ISWs propagating towards the east-northeast) from the Cape Ortegal region off the northwest Iberian Peninsula. Furthermore, the imagery revealed, for the first time, evidence of “local generation” of ISWs off southwest Portugal, travelling both offshore (two sets of waves, generated after reflections of internal tidal rays from the sea floor) and onshore (one example, generated directly by an upward ray without a bottom reflection)
Internal solitary waves on the Saya de Malha bank of the Mascarene Plateau: SAR observations and interpretation
No full textEnergetic Internal Solitary Waves (ISWs) were recently discovered radiating from the central region of the Mascarene Plateau in the south-western Indian Ocean (da Silva et al., 2011). SAR imagery revealed the two-dimensional structure of the waves which propagated for several hundred kilometres in deep water both to the east and west of a sill, located near 12.5°S, 61°E between the Saya de Malha and Nazareth banks. These waves were presumed to originate from the disintegration of a large lee wave formed on the western side of the sill at the time of maximum barotropic flow to the west. In the present paper we focus instead on ISWs propagating in the shallow water above the Saya da Malha (SM) bank (to the north of the sill), rather than on those propagating in deep water (here denominated as type-I or -II waves if propagating to the west or east respectively). Analysis of an extended SAR image dataset reveals strong sea surface signatures of complex patterns of ISWs propagating over the SM bank arising from different sources. We identify three distinct types of waves, and propose suitable generation mechanisms for them using synergy from different remotely sensed datasets, together with analyses of linear phase speeds (resulting from local stratification and bathymetry). In particular, we find a family of ISWs (termed here A-type waves) which results from the disintegration of a lee wave which forms on the western slopes of SM. We also identify two further wave trains (B- and C-type waves) which we suggest result from refraction of the deep water type-I and -II waves onto the SM bank. Therefore, both B- and C-type waves can be considered to result from the same generation source as the type-I and -II waves. Finally, we consider the implications of the ISWs for mixing and biological production over the SM bank, and provide direct evidence, from ocean colour satellite images, of enhanced surface chlorophyll over a shallow topographic feature on the bank, which is consistent with the breaking of the ISWs
The IOSDL towed thermistor spar on MV "Sea Searcher" in the Iceland Faeroes region April/May 1988
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