Fahrtbericht Poseidon-Reise 222-1/2 [POS222-1/2], Abschnitt 1: Reykjavik-Reykjavik 7.8.-12.8.1996, Abschnitt 2: Reykjavik-Reykjavik 13.8.-28.8.1996 : Overflow '96

Fahrtgebiet: Irmingersee und Ausgang Dänemarkstraße Zweck: Hydrographische Aufnahme im Ausbreitungsgebiet des Overflow-Wassers, Auslegung einer Inverted Echo Sounder Verankerung (I.E.S), Auslegung von satelliten-georteten Driftbojen, Schleppen eines neuen geomagnetischen Elektrokinetographs (TTM3), Erprobung eines GPS-Arrays zur hochgenauen Ortsbestimmung Wiss. Ziele: Ermittlung mesoskaliger Strukturen im Overflow als Eingangsdaten für Simulationsrechnunge

Bericht des Fahrtleiters "Poseidon"-Reise Nr. 86, Abschnitte 1 und 2, 15.3.1982 bis 15.4.1982 [POS86]

Das Teilprojekt C2 des SFB 133 "Warmwassersphäre des Atlantiks" untersucht die mesoskalige Variabilität des Dichte- und Strömungsfeldes im Kanarenbecken. Im Vordergrund der diesjährigen Untersuchungen steht die Frage, in welchem Masse die Zirkulation im Tiefenbereich bis etwa 1500 m durch hydrographische Messungen erfasst werden kann und mit direkten Strömungsmessungen aus verankerten Meßsystemen bzw. aus satelliten-georteten Driftbojen in Einklang zu bringen ist. Da eine quasi-synoptische Aufnahme eines grösseren Areals bisher noch nicht zur Verfügung steht, sollte FS "Poseidon" während der Expedition "KANARENBECKEN 1982" die hydrographische Vermessung eines etwa 200 x 200 sm grossen Gebietes vornehmen, in dem die mesoskalige Aktivität besonders gross war. Meridionale Schnitte während der "METEOR"-Reise 56 (Abschnitt 5, Rückreise Antarktis) hatten gezeigt, daß im Bereich um 33°N, 22°W, im Frühjahr ein System von Temperatur-Salzgehaltsfronten vorhanden ist. Es lag nahe, daß diese Fronten mit starken Oberflächenströmungen verbunden waren. Daher wurde der Einsatz von 4 satellitengeorteten Driftbojen mit Segel in 100 m Tiefe vorgesehen, die bereits 14 Tage vor dem Beginn des Experiments durch FS "METEOR" ausgelegt werden sollten

Present-day manifestation of the Nordic Seas Overflows

Dense Nordic waters enter the North Atlantic through passages in the Greenland-Scotland Ridge at a mean rate of 6 Sv. Subsequent entrainment of ambient water into the sinking plumes downstream of the sills approximately double this flux. Decade-long observations show these fluxes to be stable with no discernible trends. Hydraulic control of the overflows and the buffering effect of the Nordic basins effectively filter out short-term variability of dense water production associated with white noise North Atlantic Oscillation forcing. Simulations with directly forced and coupled atmosphere-ocean models show, under present climate conditions, overflow variability on multi-decadal time scales but no longterm trends

Internal wave kinematics in the upper tropical Atlantic

Horizontal velocity and temperature measurements observed from a two-dimensional array of moored instruments, mooring Fl, are analysed to describe the near-surface internal wave field in the GATE (GARP Atlantic Tropical Experiment) C-scale area. Spectral properties indicate strong deviations from the Garrett and Munk (1972, 1975) deep ocean internal wave models. The frequency spectrum in the upper pycnocline is dominated by three energetic bands centered at 0.0127 (inertial frequency), 0.08 (M2-tidal frequency) and 3 cph. The latter frequency band does not correspond to the local Brunt Väisälä frequency (< 10 cph) and contains about one half of the total internal wave energy of fluctuations with periods less than 10 hours. Cross-spectral analysis of the high frequency internal waves yields corresponding wavelengths of order 1 km consistent with westward propagating first mode wave groups, if the effect of Doppler shift due to a strong mean current is taken into accoun

A linear theory of stationary coastal upwelling in a continuously stratified ocean with an unstratified shelf area

The circulation in a coastal upwelling region with a shelf area is calculated. It is assumed that the circulation on the shelf is independent of the deep-sea circulation and consists of a surface Ekman layer outflow, a coastal boundary layer upwelling and a bottom Ekman layer inflow. The resultant velocity distribution is used as a boundary condition for the deep-sea circulation...

A note on near-surface VACM measurements made from three different kinds of surface moorings

During a multi-institutional air-sea interaction experiment (GATE) in the central Atlantic North Equatorial Countercurrent in September 1974, vector-averaging current meter (VACM) measurements were made within the 30-m thick mixed layer from three different types of surface moorings. The moorings consisted of a single-point taut-line flexible mooring (E3), a spar-buoy (El), and a 2-legged mooring (Fl). Although the kinetic energy density spectral estimates of the E3, El, and Fl records in the low frequency range were equivalent with 95% confidence, the mean progressive vector diagrams differed by 6 % in length and 4 in direction. At frequencies above 1 cph the variances of the 7.2 m Fl current vectors were about 1.5 times larger than the 7.6 m E3 data and the spectral levels of the 20 m El and 21.4 m E3 record were equivalent, suggesting that VACM current vectors recorded near the surface beneath a surface-following buoy do not contain detectable amounts of aliased high-frequency mooring motion

A quasi-synoptic survey of the thermocline circulation and water mass distribution within the Canary Basin

Shipboard hydrographic measurements and moored current meters are used to infer both the large-scale and mesoscale water mass distribution and features of the general circulation in the Canary Basin. We found a convoluted current system dominated by the time-dependent meandering of the eastward flowing Azores Current and the formation of mesoscale eddies. At middepths, several distinctly different water masses are identified: Subpolar Mode and Labrador Sea Water are centered in the northwest, Subantarctic Intermediate Water is centered in the southeast, and the saltier, warmer Mediterranean tongue lies between them. Mesoscale structures of these water masses suggest the presence of middepth meanders and detached eddies which may be caused by fluctuations of the Azores Current

Forschungsreise 159/3 von FS POSEIDON [POS159/3] Porto - Kiel : Bericht des wissenschaftlichen Leiters

Zeitplan: 9. Juni 1989 Auslaufen Porto, 26. Juni Einlaufen Kie