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Attributing mean circulation patterns to physical phenomena in the Gulf of Finland

Westerlund A., Tuomi L., Alenius P., Miettunen E., Vankevich R. E.

Oceanologia

2018

No. 60 (1)

16--31

We studied circulation patterns in the Gulf of Finland, an estuary-like sub-basin of the Baltic Sea. According to previous observations and model results, the long-term mean circulation in the gulf is cyclonic and mainly density driven, whereas short-term circulation patterns are wind driven. We used the high-resolution 3D hydrodynamic model NEMO to simulate the years 2012-2014. Our aim was to investigate the role of some key features, like river runoff and occasional events, in the formation of the circulation patterns. Our results show that many of the differences visible in the annual mean circulation patterns from one year to another are caused by a relatively small number of high current speed events. These events seem to be upwelling-related coastal jets. Although the Gulf of Finland receives large amounts of fresh water in river runoffs, the inter-annual variations in runoff did not explain the variations in the mean circulation patterns.

Large halocline variations in the Northern Baltic Proper and associated meso- and basin-scale processes

Elken J., Mälkki P., Alenius P., Stipa T.

Oceanologia

2006

No. 48 (S)

91-117

The Northern Baltic Proper is a splitting area of the Baltic Sea saline water route towards the two terminal basins - the Gulf of Finland and the Western Gotland Basin. Large halocline variations (vertical isopycnal displacements of more than 20 m, intra-halocline current speeds above 20 cm s-1 appear during and following SW wind events, which rapidly increase the water storage in the Gulf of Finland and reverse the standard estuarine transport, causing an outflow in the lower layers. In the channel of variable topography, basin-scale barotropic flow pulses are converted into baroclinic mesoscale motions such as jet currents, sub-surface eddies and low-frequency waves. The associated dynamics is analysed by the results from a special mesoscale experiment, routine observations and numerical modelling.