Flow regime in the Irbe Strait

The current structure in a strait connecting a semi-enclosed bay and the Baltic Sea is studied on the basis of data obtained during the Gulf of Riga Project in 1993-1995. The observations comprised hydrographic snapshots and a 10-day intense campaign IRBEX-95 of CTD, current, sea-level and meteorological measurements. The baroclinic forcing due to the density difference, the barotropic forcing due to the sea-level difference, and the wind forcing are considered as factors driving the water flow through the Irbe Strait. A regular flow scheme (outflow in the northern part and inflow near the southern slope of the strait) which is related to the quasi-permanent salinity front was shown to prevail on average. Current oscillations having inertial and diurnal periods and forcing-dependent current fluctuations are frequently observed to be superimposed on the mean structure of the currents. A relatively quick response of the hydrographic fields to almost periodic (2-day) changes of the local wind and the sea level is stated. The current is preferably contra-directional to the wind stress, but well correlated with the sea level difference between the open sea and the strait. However, the described regular current scheme seems to contribute the most to the water, salt and nutrient exchange through the Irbe Strait.