Description: OceanRep OceanRep Home Contact Quick Search Simple Search Advanced Search Browse Author Research division Document type Year Course of Study Latest Peer-reviewed Articles All About us GEOMAR Library Open Access Policies Statements Help FAQs Statistics Directions | Contact | Sitemap | Imprint Zur Kinematik eines stochastischen Feldes interner Wellen in einer Scherströmung. Logged in as Barbara Schmidt Manage depositsManage recordsManage shelvesProfileSaved searchesReviewAdminLogout - Tools Peters, Hartmut (1981) Zur Kinematik eines stochastischen Feldes interner Wellen in einer Scherströmung. (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 118 pp. [img] Text Diss. 1981 Peters, H.pdf - Published Version Restricted to Registered users only Download (7Mb) Abstract Für die im Atlantik im Bereich des Äquatorialen Gegenstroms während GATE beobachtete mittlere Schichtung und Scherströmung werden vertikale Eigenschwingungen (Moden) und Dispersionskurven hochfrequenter (0.3 bis 15 cph) interner Wellen berechnet. Ein spektrales Modell der Kinematik freier, linearer interner Wellen wird durch die stochastische Überlagerung so gewonnener Moden erzeugt. Modellrechnungen werden zu Vergleichs- und Testzwecken für einfache Grundzustände (N 2 = const.; u = const.) durchgeführt. Die den Verhältnissen während GATE entsprechenden Rechnungen ergeben folgende Resultate: In den Energiespektren wird eine Schulter bei Frequenzen zwischen 1.5 und 4 cph beobachtet, die einen nicht unbeträchtlichen Teil der Gesamtenergie des Wellenfeldes repräsentiert. Diese Schulter kann im wesentlichen nicht durch kinematische Effekte erklärt werden, sie muß dynamische Ursachen haben. Im Frequenzbereich 1.5 bis 4 cph wird das Wellenfeld praktisch ausschließlich von der ersten Mode beherrscht. Nach den Beobachtungen sind die Wellen überwiegend gegen die mittlere Strömung gerichtet. Zur Erklärung dessen müssen sowohl dynamische als auch kinematische Effekte herangezogen werden. Das beobachtete Maximum der Kohärenz zwischen Strömung in der Deckschicht und Temperatur in der Sprungschicht zwischen 1. 5 und 4 cph ist prinzipiell der Kinematik des Systems zuzuschreiben. Die Skalen des Wellenzahlspektrums, die sich aus der Anpassung des Modells an die Daten ergeben, sind derart, daß nur ein Teil der Anisotropie des Systems von Moden und Dispersionskurven wirksam wird. Die Vertikalstruktur der beobachteten Strömungsfluktuationen kann mit dem Modell nicht vollständig beschrieben werden. Das Modell wird kritisch diskutiert.

Description: Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 569–583, doi:10.1175/JPO2679.1.

Description: When the salty and heavy water of the Red Sea exits from the Strait of Bab el Mandeb, it continues downslope into the Gulf of Aden mainly along two channels. The 130-km-long “Northern Channel” (NC) is topographically confined and is typically only 5 km wide. In it, the Red Sea plume shows unanticipated patterns of vertical structure, turbulent mixing, and entrainment. Above the seafloor a 25–120-m-thick weakly stratified layer shows little dilution along the channel. Hence this bottom layer undergoes only weak entrainment. In contrast, a 35–285-m-thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing. It is thus the interface that exhibits the bulk of entrainment of the Red Sea plume in the NC. The interfacial layer also carries most of the overall plume transport, increasingly so with downstream distance. The “Southern Channel” (SC) is wider than the NC and is accessed from the latter by a sill about 33 m above the floor of the NC. Entrainment into the bottom layer of the SC is diagnosed to be strong near the entry into the SC such that the near-bottom density and salinity are smaller in the SC than in the NC at the same distance from Bab el Mandeb. In comparison with winter conditions, the authors encountered weaker outflow with shallower equilibration depths during the summer cruise. Bulk Froude numbers computed for the whole plume varied within the range 0.2–1. Local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment.

Description: The Red Sea Outflow Experiment was funded by the National Science Foundation under Contracts OCE-9819506 and OCE-9818464. Additional support was provided to the “Climate Process Team Gravity Currents” under OCE-0336799.

Description: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C12005, doi:10.1029/2007JC004145.

Description: We have evaluated a regional-scale simulation of the Mediterranean outflow by comparison with field data obtained in the 1988 Gulf of Cádiz Expedition. Our ocean model is based upon the Hybrid Coordinate Ocean Model (HYCOM) and includes the Richardson number–dependent entrainment parameterization of Xu et al. (2006). Given realistic topography and sufficient resolution, the model reproduces naturally the major, observed features of the Mediterranean outflow in the Gulf of Cádiz: the downstream evolution of temperature, salinity, and velocity profiles, the mean path and the spreading of the outflow plume, and most importantly, the localized, strong entrainment that has been observed to occur just west of the Strait of Gibraltar. As in all numerical solutions, there is some sensitivity to horizontal and vertical resolution. When the resolution is made coarser, the simulated currents are less vigorous and there is consequently less entrainment. Our Richardson number–dependent entrainment parameterization is therefore not recommended for direct application in coarse-resolution climate models. We have used the high-resolution regional model to investigate the response of the Mediterranean outflow to a change in the freshwater balance over the Mediterranean basin. The results are found in close agreement with the marginal sea boundary condition (MSBC): A more saline and dense Mediterranean deep water generates a significantly greater volume transport of the Mediterranean product water having only very slightly greater salinity.

Description: National Science Foundation via grant OCE0336799 and the National Ocean Partnership Program (NOPP) via award N000140410676.

Description: Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1963–1985, doi:10.1175/JPO2787.1.

Description: Hydrographic, direct velocity, and subsurface float observations from the 2001 Red Sea Outflow Experiment (REDSOX) are analyzed to investigate the gravitational and dynamical adjustment of the Red Sea Outflow Water (RSOW) where it is injected into the open ocean in the western Gulf of Aden. During the winter REDSOX cruise, when outflow transport was large, several intermediate-depth salinity maxima (product waters) were formed from various bathymetrically confined branches of the outflow plume, ranging in depth from 400 to 800 m and in potential density from 27.0 to 27.5 σθ, a result of different mixing intensity along each branch. The outflow product waters were not dense enough to sink to the seafloor during either the summer or winter REDSOX cruises, but analysis of previous hydrographic and mooring data and results from a one-dimensional plume model suggest that they may be so during wintertime surges of strong outflow currents, or about 20% of the time during winter. Once vertically equilibrated in the Gulf of Aden, the shallowest RSOW was strongly influenced by mesoscale eddies that swept it farther into the gulf. The deeper RSOW was initially more confined by the walls of the Tadjura Rift, but eventually it escaped from the rift and was advected mainly southward along the continental slope. There was no evidence of a continuous boundary undercurrent of RSOW similar to the Mediterranean Undercurrent in the Gulf of Cadiz. This is explained by considering 1) the variability in outflow transport and 2) several different criteria for separation of a jet at a sharp corner, which indicate that the outflow currents should separate from the boundary where they are injected into the gulf.

Description: This work was supported by the U.S. National Science Foundation under Grants OCE-9818464 (WHOI) and OCE-9819506 (RSMAS).

Description: Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 90 (2009): 657-670, doi:10.1175/2008BAMS2667.1.

Description: Oceanic overflows are bottom-trapped density currents originating in semienclosed basins, such as the Nordic seas, or on continental shelves, such as the Antarctic shelf. Overflows are the source of most of the abyssal waters, and therefore play an important role in the large-scale ocean circulation, forming a component of the sinking branch of the thermohaline circulation. As they descend the continental slope, overflows mix vigorously with the surrounding oceanic waters, changing their density and transport significantly. These mixing processes occur on spatial scales well below the resolution of ocean climate models, with the result that deep waters and deep western boundary currents are simulated poorly. The Gravity Current Entrainment Climate Process Team was established by the U.S. Climate Variability and Prediction (CLIVAR) Program to accelerate the development and implementation of improved representations of overflows within large-scale climate models, bringing together climate model developers with those conducting observational, numerical, and laboratory process studies of overflows. Here, the organization of the Climate Process Team is described, and a few of the successes and lessons learned during this collaboration are highlighted, with some emphasis on the well-observed Mediterranean overflow. The Climate Process Team has developed several different overflow parameterizations, which are examined in a hierarchy of ocean models, from comparatively well-resolved regional models to the largest-scale global climate models.

Description: The Gravity Current Entrainment Climate Process Team was funded by NSF grants OCE-0336850 and OCE-0611572 and NOAA as a contribution to U.S.CLIVAR.

Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C09039, doi:10.1029/2005JC003338.

Description: New satellite-based observations reveal that westward translating anticyclonic rings are generated as a portion of the Somali Current accelerates northward through the Socotra Passage near the mouth of the Gulf of Aden. Rings thus formed exhibit azimuthal geostrophic velocities exceeding 50 cm/s, are comparable in overall diameter to the width of the Gulf of Aden (250 km), and translate westward into the gulf at 5–8 cm/s. Ring generation is most notable in satellite ocean color imagery in November immediately following the transition between southwest (boreal summer) and northeast (winter) monsoon regimes. The observed rings contain anomalous fluid within their core which reflects their origin in the equator-crossing Somali Current system. Estimates of Socotra Passage flow variability derived from satellite altimetry provide evidence for a similar ring generation process in May following the winter-to-summer monsoon transition. Cyclonic recirculation eddies are observed to spin up on the eastern flank of newly formed rings with the resulting vortex pair translating westward together. Recent shipboard and Lagrangian observations indicate that vortices of both sign have substantial vertical extent and may dominate the lateral circulation at all depths in the eastern Gulf of Aden.

Description: This investigation is a component of the Red Sea Outflow Experiment (REDSOX) sponsored by the U.S. National Science Foundation through grants OCE 98-18464 and OCE 04-24647 to the Woods Hole Oceanographic Institution and OCE 98-19506 and OCE 03-51116 to the University of Miami.