Vortex merger near a topographic slope in a homogeneous rotating fluid

This work is a contribution to the PHYSINDIEN research program. It was supported by CNRS-RFBR contract PRC 1069/16-55-150001.The effect of a bottom slope on the merger of two identical Rankine vortices is investigated in a two dimensional, quasi-geostrophic, incompressible fluid. When two cyclones initially lie parallel to the slope, and more than two vortex diameters away from the slope, the critical merger distance is unchanged. When the cyclones are closer to the slope, they can merge at larger distances, but they lose more mass into filaments, thus weakening the efficiency of merger. Several effects account for this: the topographic Rossby wave advects the cyclones, reduces their mutual distance and deforms them. This along shelf wave breaks into filaments and into secondary vortices which shear out the initial cyclones. The global motion of fluid towards the shallow domain and the erosion of the two cyclones are confirmed by the evolution of particles seeded both in the cyclone sand near the topographic slope. The addition of tracer to the flow indicates that diffusion is ballistic at early times. For two anticyclones, merger is also facilitated because one vortex is ejected offshore towards the other, via coupling with a topographic cyclone. Again two anticyclones can merge at large distance but they are eroded in the process. Finally, for taller topographies, the critical merger distance is again increased and the topographic influence can scatter or completely erode one of the two initial cyclones. Conclusions are drawn on possible improvements of the model configuration for an application to the ocean.PostprintPeer reviewe

Spatial and temporal variability of selected trace metals in Kiel Bight and Mecklenburg Bight Data report from 1990/92

Water samples from the surface layer (7 m depth) and from bottom water (2 m above the bottom) were collected on six separate cruises from a network of 27 stations in Kieler Bucht and Mecklenburger Bucht during a three year period (February 1990-July 1992) in order to estimate the spatial and temporal variability of Co, Pb, Cd, Cu, Ni, Fe, Zn, and Mn in the dissolved (<0.4 #mu#m diameter) and particulate phases. Total Hg in unfiltered water samples was also determined. Standard hydrographic parameters, nutrients, dissolved O_2, particulate organic C and N, and suspended particulate matter (SPM) were also measured. (The entire data base measures a total of approximately 10,200 data points.) Results are presented in this report as summary tables of mean data for surface and bottom waters in summer and winter seasons, and in figures showing mean surface and bottom water concentrations seasonally at each station. Statistical differences at the p=0.01 probability level are tabulated for hydrochemical parameters, dissolved metals, and particulate metals in four different comparison types (summer surface water vs summer bottom water, winter surface vs winter bottom, surface water in summer vs winter, and bottom water in summer vs winter). In addition, comparisons of dissolved and particular trace elements to hydrochemical and biological parameters are presented, in order to clarify the biogeochemical processes in the study area. (orig.)Ueber einen Zeitraum von 3 Jahren (Februar 1990-Juli 1992) wurden auf 6 verschiedenen Fahrten und von 27 Stationen in der Kieler und Mecklenburger Bucht Wasserproben aus der Deckschicht (7 m) und dem Tiefenwasser (2 m ueber Grund) entnommen, um die raeumliche und zeitliche Variabilitaet der geloesten (<0.4 #mu#m) und partikulaeren Konzentrationen von Co, Pb, Cd, Cu, Ni, Fe, Zn, Mn in diesem Gebiet zu untersuchen. Auch die gesamt-Hg Konzentrationen von unfiltrierten Wasserproben wurden bestimmt. Ausserdem sind die hydrochemischen Parameter (Temperatur, Salz-, Sauerstoff- und Naehrstoffgehalte), der Gehalt an part. organischem C und N (POC/PON), sowie die Konzentrationen von Chlorophyll a und des suspendierten partikulaeren Materials (SPM) gemessen worden. (Die gesamte Datenbasis dieses Vorhabens umfasst etwa 10.200 Einzelmessungen.) Die Ergebnisse werden in diesem Datenbericht in Form von Tabellen und Abbildungen einmal als Vergleich der Stationsmittelwerte fuer vier verschiedene Wassermassen-Typen dargestellt (Oberflaechenwasser im Sommer gegen Tiefenwasser im Sommer; Oberflaechenwasser in Winter gegen Tiefenwasser im Winter; Oberflaechenwasser im Sommer gegen Winter sowie Tiefenwasser im Sommer gegen Winter). Dabei wird fuer die Signifikanz der Differenzen eine Wahrscheinlichkeit von p=0.01 angesetzt. Zum anderen werden die Konzentrationen der geloesten und partikulaeren Spurenelemente in den einzelnen Wassermassen gegen die hydrochemischen und biologischen Parameter aufgetragen, um die biogeochemischen Prozesse in diesem Gebiet zu verdeutlichen. (orig.)SIGLEAvailable from TIB Hannover: RN 3292(238) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman