Variability of the baroclinic Rossby radius in the Gulf of Finland

The internal Rossby radius, R1, and its variability over the Gulf of Finland has been determined on the basis of 1911 hydrographic soundings made during the years 1993–1999. It was found that R1 has a large spatial and temporal variability. The largest values of R1 were observed in summer in deep parts of the Gulf. In shallow coastal regions and in the eastern Gulf of Finland, R1 is smaller than in the open deep areas. Average values of R1 were 2.1 km in shallow areas (depth <36 m) and 4.1 km in the open sea. The smallest R1 values were of the order of some hundreds of metres, whilst the largest were over 7 km. Typical values (approximately 70% of all the observations) of R1 in the Gulf of Finland fall within the range 2–4 km; which was less than half of the corresponding values in the Gotland Deep, where reference data provided an average value of 10.9 km. The seasonal variability of R1 was also pronounced. The largest values occur in late summer, when the temperature stratification is at its strongest. Short-scale variability of R1 on a time-scale of some hours was also identified.