286
T. Soomere
transport is much more challenging even for surface currents (Vandenbulcke et al.
2009).
The presented results are thus directly applicable for persistent neutrally buoyant
substances that are dissolved in strongly stratified environments under calm conditions when the contaminants (e.g., dissolved radioactive substances) largely remain
in the uppermost layer and are mostly carried by surface currents (e.g., Periáñez
2004). This setup is only conditionally valid for oil pollution, lost containers, vessels without propulsion, debris, litter, etc., as it does not consider other metocean
drivers, chemical processes, buoyancy effects, weathering of oil, and so forth.
The use of the simulated field of currents to calculate the drift of dissolved substances and objects located within the uppermost layer is most applicable in the
Gulf of Finland during a large part of the spring and early summer when the wind is
fairly weak (below 5 m/s) (Mietus 1998) and also during the presence of ice cover
(up to six months in some years) (Jevrejeva and Leppäranta 2002; Sooäär and Jaagus 2007) when the field of currents is almost totally disconnected from the direct
atmospheric influence. The setup in use is therefore of clear value to improve the
understanding about the potential role of a practical use of the intrinsic dynamics
of currents to preventively reduce the costs of accidents at sea (Soomere and Quak
2007).
This chapter demonstrates the potential of the analysis of Lagrangian trajectories
of water particles to identify usually concealed semi-persistent patterns and associated Lagrangian transport driven by surface currents in areas hosting extremely
complicated systems of currents. The focus is on two areas of the Baltic Sea—the
Gulf of Finland and the south-western (SW) region of the Baltic Sea. The basic tool
is the statistical analysis of properties of a large number of Lagrangian trajectories
constructed from precomputed Eulerian velocity fields. A similar technique (but in
an Eulerian framework) has been applied in Chap. 4. The same technique will be
used in Chaps. 10 and 11 to evaluate the environmental risks, to identify the areas
of reduced risk and to find optimum fairways for the test areas. The technique relies
on a specific discretization of the direct problem of propagation of passive tracers.
This discretization contains several time scales and other parameters, the optimum
choice of which is analysed based on examples from the two test areas. Finally, the
developed technique is applied to identify several normally concealed features of
the dynamics of the Gulf of Finland.
9.2 Hydrodynamics of the Test Regions
The two test regions, the Gulf of Finland and SW Baltic Sea, not only host extremely
dense ship traffic but also play in a certain sense a key role in the functioning of
the entire Baltic Sea. The major marine highway approaches the Baltic Sea via the
Kattegat and Kiel Channel, branches into two flows through the Danish Straits and
merges back into a powerful flux in the Arkona Basin (Fig. 9.2). Its major branch
T. Soomere
transport is much more challenging even for surface currents (Vandenbulcke et al.
2009).
The presented results are thus directly applicable for persistent neutrally buoyant
substances that are dissolved in strongly stratified environments under calm conditions when the contaminants (e.g., dissolved radioactive substances) largely remain
in the uppermost layer and are mostly carried by surface currents (e.g., Periáñez
2004). This setup is only conditionally valid for oil pollution, lost containers, vessels without propulsion, debris, litter, etc., as it does not consider other metocean
drivers, chemical processes, buoyancy effects, weathering of oil, and so forth.
The use of the simulated field of currents to calculate the drift of dissolved substances and objects located within the uppermost layer is most applicable in the
Gulf of Finland during a large part of the spring and early summer when the wind is
fairly weak (below 5 m/s) (Mietus 1998) and also during the presence of ice cover
(up to six months in some years) (Jevrejeva and Leppäranta 2002; Sooäär and Jaagus 2007) when the field of currents is almost totally disconnected from the direct
atmospheric influence. The setup in use is therefore of clear value to improve the
understanding about the potential role of a practical use of the intrinsic dynamics
of currents to preventively reduce the costs of accidents at sea (Soomere and Quak
2007).
This chapter demonstrates the potential of the analysis of Lagrangian trajectories
of water particles to identify usually concealed semi-persistent patterns and associated Lagrangian transport driven by surface currents in areas hosting extremely
complicated systems of currents. The focus is on two areas of the Baltic Sea—the
Gulf of Finland and the south-western (SW) region of the Baltic Sea. The basic tool
is the statistical analysis of properties of a large number of Lagrangian trajectories
constructed from precomputed Eulerian velocity fields. A similar technique (but in
an Eulerian framework) has been applied in Chap. 4. The same technique will be
used in Chaps. 10 and 11 to evaluate the environmental risks, to identify the areas
of reduced risk and to find optimum fairways for the test areas. The technique relies
on a specific discretization of the direct problem of propagation of passive tracers.
This discretization contains several time scales and other parameters, the optimum
choice of which is analysed based on examples from the two test areas. Finally, the
developed technique is applied to identify several normally concealed features of
the dynamics of the Gulf of Finland.
9.2 Hydrodynamics of the Test Regions
The two test regions, the Gulf of Finland and SW Baltic Sea, not only host extremely
dense ship traffic but also play in a certain sense a key role in the functioning of
the entire Baltic Sea. The major marine highway approaches the Baltic Sea via the
Kattegat and Kiel Channel, branches into two flows through the Danish Straits and
merges back into a powerful flux in the Arkona Basin (Fig. 9.2). Its major branch