Description: Due to the ephemeral nature of the atmospheric conditions over the Baltic Sea, the flow field is highly variable, and thus, changes in the resulting circulation and upwelling are difficult to observe. However, three-dimensional models, forced by realistic atmospheric conditions and river runoff, have reached such a state of accuracy that the highly fluctuating current field and the associated evolution of the temperature and salinity field can be described. In this work, effects of remote and local atmospheric forcing on circulation and upwelling in the Baltic Sea are investigated. Changes in the characteristics of the large-scale atmospheric wind field over the central and eastern North Atlantic can be described by the North Atlantic Oscillation (NAO). The NAO is related to the strength and geographical position of weather systems as they cross the North Atlantic and thus has a direct impact on the climate in Europe. To relate the local wind field over the Baltic Sea to the large-scale atmospheric circulation, we defined a Baltic Sea Index (BSI), which is the difference of normalised sea level pressures between Oslo in Norway and Szczecin in Poland. The NAO is significantly related to the BSI. Furthermore, the BSI is highly correlated with the storage variation of the Baltic Sea and the volume exchange through the Danish Sounds. Based on three-dimensional model calculations, it is shown that different phases of the NAO during winter result in major changes of horizontal transports in the deep basins of the Baltic Sea and in upwelling along the coasts as well as in the interior of the basins. During NAO+ phases, strong Ekman currents are produced with increased up- and downwelling along the coasts and associated coastal jets, whereas during NAO− phases, Ekman drift and upwelling are strongly reduced, and the flow field can almost entirely be described by the barotropic stream function. The general nature of the mean circulation in the deep basins of the Baltic Sea, obtained from a 10-yr model run, can be described by the depth integrated vorticity balance derived from the transport equation for variable depth.

Description: If only the periode of internal waves is governed by tide generating force the wave length is a free parameter. Then in a two-layered ocean (horicontal unbounded) internal waves with large amplitude and with the same periode as tide generating force are possible. The wave length of these waves corresponds to the case of resonance which follows from theory of free waves.

Description: Mit Hilfe des Verfahrens von J. W. TUKEY werden gefilterte und ungefilterte Energie- bzw. Amplitudenspektren der Wasserstandsschwankungen des Jahres 1958 an 31 Pegelstationen entlang der Ostseeküste berechnet (Durchlaßbereich des Filters 6h-50h). Für benachbarte Stationen werden ferner Co- uncl Quadratur-Spektren sowie Phasendifferenz und Kohärenz berechnet. Aus den Spektren der gefilterten Meßreihen wird die Verteilung der Amplituden der S2-, M2-, K1- und O1-Tide ermittelt. Dabei wird unterschieden zwischen den Amplituden, die der Gesamtenergie im Spektrum bei den Gezeitenperioden entsprechen und denjenigen, die aus der Energiedifferenz zwischen der Gesamtenergie und der mittleren Energie des meteorologisch bedingten Spektralniveaus resultieren. Die ungefilterten Spektren zeigen mit Ausnahme der Stationen des Finnischen Meerbusens eine Energiekonzentration im Bereich von etwa 120h. Es wird eine spezielle Situation gefunden, in der die Wasserstände weitgehend durch eine 120-stündige Periodizität beschrieben werden können. Diese Periodizität erweist sich als stehende, winderzeugte Welle. Energy and amplitude spectra with and without a bandpass filter from 6h-50h of the 1958 sea level records from 31 tide gauges along the coast of the Baltic have been computed by means of the method of J. W. TUKEY. For neighbouring stations co- and quadrature-spectra, phase difference and coherence have also been computed. The amplitude and phase distribution of the S2, M2, K1 and 01 tide have been derived from the filtered spectra. The amplitudes corresponding to the total energy at the tidal periods and those resulting from the energy difference between the total energy and the noise energy are given separately. The spectra computed without filtering show an energy concentration in the range of about 120h except at the stations of the Gulf of Finland. A special situation has been found where the water level can be described by a 120h periodicity to a large extent. This periodicity turns out to be a standing wave forced by wind.