Eberhard Hagen

Northwest African upwelling scenario

Abstract Observations, hypotheses and derived scenarios are discussed for the Northwest-African coastal upwelling area. The process of coastal upwelling is considered to be composed of a climatic steady-state part and fluctuations acting on different spatial and temporal scales. Attention is focused on disturbances acting globally on the inter-annual time-scale. El Nino-like changes occur in the system of trade winds and modify the equatorial regime of currents as well as the coastal upwelling regimes on both flanks of the Inter-tropical Convergence Zone. There is an opposite thermal response in near-surface layers along the zonal coast in the Gulf of Guinea and along the meridional coast off NW-Africa. Off the continental slope of Senegal and Mauritania, the poleward undercurrent is linked with the system of eastward flowing equatorial undercurrents via the transport of South Atlantic Central Water (SACW) around the eastern flank of the Guinea Dome. The upwelling undercurrent partly feeds its SACW properties into the belt of coastal upwelling and contributes significantly to the biological productivity during ‘normal’ and ‘abnormal’ upwelling years. Future investigations should focus on changes in the time-scale of decades.

On the GIBBS thermodynamic potential of seawater

Abstract Free Enthalpy, the GIBBS thermodynamic potential G(S,t,p) of seawater, has been recomputed including the sound speed equation of Del Grosso (1974), temperatures of maximum density (TMD) of Caldwell (1978), freezing point depression measurements of Doherty and Kester (1974), rederived limiting laws and ice properties, and an extended set of dilution heat data of Bromley (1968) and Millero, Hansen and Hoff (1973). As a new reference state, the standard ocean state has been chosen. The resulting average deviations are 0.0006 kg m −3 for pure water density at 1 atm, 0.002 kg m −3 for seawater density at 1 atm, 0.02 m/s for sound speed, 0.01 J kgK −1 for heat capacity at 1 atm, 0.4 kJ kg −1 for dilution heats, 0.002°C for freezing points, and 0.04°C for TMDs. Resulting pressure-dependent freezing points are in good agreement with experiments and UNESCO (1978) formulas. Enthalpy as thermodynamic potential has been explicitly determined for easy computation of potential temperature, potential density, and sound speed. All functions are expressed in the new International Temperature Scale ITS-90.

A Gibbs thermodynamic potential of sea ice

Abstract A thermodynamic potential function for air-free sea ice, specific Gibbs free energy (free enthalpy) G(s,t,p), has been computed in terms of sea ice salinity s, temperature t and pressure p. Its numerical application is restricted to brine salinities up to 40 g/kg and to applied pressures not exceeding 10 MPa. Using the assumption of brine–ice equilibrium the Gibbs potential is derived from Gibbs free energies of seawater and of pure water ice. Explicit mathematical expressions are deduced theoretically for various thermodynamic properties of sea ice including, e.g., specific heat at constant pressure, isothermal compressibility, isobaric thermal volume expansion coefficient, isochoric pressure coefficient, and temperature of maximum volume. Care is taken for pressure dependencies of all properties and for appropriate salinity root expansions due to Debye–Huckel theory of electrolytic solutions. Simplified computation formulas are proposed for some important quantities.

Meteorologie und Ozeanographie

Meteorologie und Ozeanographie stehen in einer vielfaltigen Wechselwirkung von physikalischen Prozessen. Daraus resultiert ein groser Einflus auf das Klima, der besonders stark in den meeresnahen Gebieten ist. Man unterscheidet daher ozeanisches von kontinentalem Klima, die beide im Ostseeraum aufgrund seiner geographischen Lage wirksam sind. Im folgenden werden Klima und Witterung sowie die physikalische Ozeanographie behandelt.