Synoptic Variability of Current in the Baltic Proper.

Abstract

This chapter discusses the synoptic variability of currents in the Baltic proper. The discovery of synoptic scale variability is one of the results of several experiments conducted in different parts of the World Ocean during the past two decades. Phenomena of synoptic scale include open sea eddies, Rossby waves, topographic waves and topographic Rossby waves, and baroclinic instabilities of large scale motion of the ocean. The direct measurement of currents using autonomous mooring stations is one of the most reliable methods for studying the synoptic scale processes. If the bottom slope is decreased, the amplitude of unstable waves doubles more rapidly, their wavelengths become shorter, and their periods longer. However, an increase in the mean velocities shortens both the lengths and the periods of unstable waves and the amplitudes of unstable waves double much more rapidly. Furthermore, baroclinic instability is very sensitive to the direction of the current in the upper layer, and if the mean current is directed so that the shallower water is to the left of the downstream direction, no baroclinic instability occurs.