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  • 1970-1974  (24)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Ocean dynamics 23 (1970), S. 214-234 
    ISSN: 1616-7228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Summary A theory of K. Hidaka [1954] on stationary coastal upwelling in a homogeneous ocean is extended to the case of a continuously stratified sea with constant Brunt-Väisälä-frequency. Stream function and density distribution are computed in a section normal to the coast for different wind fields. It is shown that the type of circulation depends essentially on the form of the wind field, wind speed influencing circulation intensity only. The depth of upwelling is inversely proportional to the square root of Brunt-Väisälä-frequency, tending towards infinity in the homogeneous case. For the same circulation, the density distribution depends strongly on diffusion and, for constant diffusion, on wind speed. Density distributions of different circulation types are very similar. Hence, from an observed density distribution, nothing can be said about the depth of upwelling and very little about the circulation.
    Abstract: Résumé On se propose ici l'extension d'une théorie de «coastal upwelling» stationnaire de K. Hidaka [1954] au cas d'un océan stratifié de façon continue, la fréquence de Väisälä étant constante. La fonction de courant et la distribution de la densité sont élaborées pour divers champs de vent, dans une section normale à la côte. Le résultat montre que le type de circulation dépend essentiellement de la distribution du vent, tandis que la vitesse du vent n'a d'influence que sur son intensité. La profondeur d'«upwelling» est inversement proportionnelle à la fréquence de Väisälä, et tendant vers l'infini dans le cas homogène. Pour une même circulation, la distribution de la densité dépend fortement de la diffusion et, pour une diffusion constante, de la vitesse du vent. Les distributions de la densité appartenant à des types différents de circulation ne se distinguent guère les unes des autres. On en déduit que d'une distribution de la densité observée, on ne peut rien dire sur la profondeur d'«upwelling» et très peu seulement sur la circulation.
    Notes: Zusammenfassung Eine Theorie von K. Hidaka [1954] des stationären küstennahen Auftriebs im homogenen Meer wird für den Fall des stetig geschichteten Meeres mit konstanter Väisälä-Frequenz erweitert. Für verschiedene Windfelder werden die Stromfunktion und die Dichteverteilung in einem küstensenkrechten Schnitt berechnet. Es ergibt sich, daß die Art der Zirkulation wesentlich von der Form des Windfeldes abhängt, während die Windstärke nur die Zirkulationsintensität beeinflußt. Die auftriebstiefe ist dabei der Wurzel aus der Väisälä-Frequenz umgekehrt proportional; im homogenen Fall wächst sie über alle Grenzen. Die Dichteverteilung ist bei gleicher Zirkulation stark von der Diffusion und bei konstanter Diffusion von der Windstärke abhängig. Zu verschiedenen Zirkulationstypen gehörende Dichteverteilungen unterscheiden sich nur wenig, voneinander. Daraus folgt, daß man aus einer beobachteten Dichteverteilung nichts über die Auftriebstiefe und sehr wenig über die Zirkulation aussagen kann.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 1382 data points
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  • 3
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 569 data points
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  • 4
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 1772 data points
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  • 5
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 1768 data points
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  • 6
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 1902 data points
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  • 7
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 363 data points
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  • 8
    Publication Date: 2019-12-19
    Type: Dataset
    Format: text/tab-separated-values, 560 data points
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  • 9
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Tomczak, Matthias (1970): Schwankungen von Schichtung und Strömung im westafrikanischen Auftriebsgebiet während der `Deutschen Nordatlantischen Expedition` 1937. Meteor Forschungsergebnisse, Deutsche Forschungsgemeinschaft, Reihe A Allgemeines, Physik und Chemie des Meeres, Gebrüder Bornträger, Berlin, Stuttgart, A7, 1-109
    Publication Date: 2019-12-20
    Description: In 1937 the "Meteor" performed the cruises of the first part of the "Deutsche Nordatlantische Expedition". This publication treats seven stations of three-day-anchoring occupied during that time, five of which are located on the shelf, one on the continental slope and one on a ridge between the Capverde islands. The Bohnecke current meter, an instrument developed for the expedition, is described briefly and it's accuracy studied by comparing the measurements of two instruments which operated simultaneously at the same depth. It is shown that it is very sensitive for movements of the anchored ship because of the very short measuring intervall (2 minutes). The influence of the ship's movements could not be eliminated completely, the mode of using the instrument at different depths being unsuitable for this. Considering the stratification the accuracy of it's representation by the mean temperature and salinity distributionis studied. It is shown that under certain conditions a distribution estimated from observed values gives more exact results. This especially applies to the TS-diagram. Station Meteor336, located on the shelf near Cape Juby, shows temperatures 4 °C less than the open ocean and so belongs to the area of upwelling. During the observation period, however, internal tides are prominent. The diurnal component is of considerable influence, the distinction from inertial oscillations (25.5 hours) not being possible, however. Station Meteor341, on the shelf off Spanish-Sahara, gives an excellent example of the movements in the centre of the area of upwelling. Changing it's direction by 45° at the beginning of the measurements, the wind causes a change of current direction at all depths which, after some inertial oscillations (period 28.3 hours), settles down to a final value. At the beginning and the end of the observations the current at the upper depths is directed off-shore, the angle between current and wind being 22°, while at the lower depths it is orientated towards the shore. The depth of the upper homogenous layer gives the origin of the water transported upwards When during the inertial oscillations the current goes offshore at all depths temporarily, a sudden disturbance occurs in the temperature measurements. Station Meteor311 is located similar to station Meteor341 but was occupied one month earlier. At that time the wind situation was unnormal, the usual wind direction of 45° occuring at the end of the station. Therefore an unnormally high vertical shear of current speed and direction has been observed, the current vector being directed off-shore at the surface and near the bottom, towards the coast inbetween. The TS-diagram shows that the bottom water is replaced first so that upwelling does not occur during observation time. The state reached at the end of the station does not seem to be stable. Station Meteor369, on the continental slope, is governed by internal waves. Besides the internal tide of 12.4 hours a wave of 6.5 hour period is observed, being possibly amplified by the large bottom slope. In 40 - 60 m depth, where the thermocline is located, a wave with 3.3 hour period is observed which is argued to be an internal boundary wave. Station Meteor334 is located on the shelf NW of the mouth of the Senegal river. A marked temperature stratification, associated with large disturbances, and nearly constant salinity have been found there. The current was going slowly towards S or SW in the upper 20 - 30 m, towards N underneath. At the boundary of the current systems intense turbulence developed,including as it seems a water type of less salinity which is transported from the Senegal river by the lower current. Station Meteor327, located at 100 m depth between two of the Capverde islands, shows oceanic characteristics. The semidiurnal tide is found mainly, the diurnal component having considerable influence. Furtheron an internal wave of 6 hour period is seen the maximum amplitude of which is moving slowly downwards. Two possibilities of explaining it are discussed. Station Meteor366 is found in the area of ceasing winds off the coast of upper Guinea. The temperature there depends strongly on the depth, the salinity being nearly constant. The currents are divided into an upper and a lower system with large variations in both of them. A change of wind direction of nearly 90° is supposed to be the reason. The variations in salinity accordingly are interpreted as the influence of fresh water outflow from land which is felt in a different way at different wind directions. In the last section the daily changes in air and water temperature are studied. The upwelling having large influence on these, a centre of the area of upwelling can be located at about 100 miles north of Cape Blanc (Station Meteor311). The semidiurnal tidal component is compared with previous results for the Atlantic Ocean yielding considerable differences for the direction and time of occurence of the current maximum which might be due to the topographical influences around the shelf.
    Type: Dataset
    Format: application/zip, 20 datasets
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  • 10
    Publication Date: 2019-12-20
    Type: Dataset
    Format: text/tab-separated-values, 556 data points
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