Chapter 9
Statistics of Lagrangian Transport Reveals
Hidden Features of Velocity Fields
Tarmo Soomere
Abstract The potential of the systematic use of Lagrangian trajectories to identify
normally hidden properties and semi-persistent patterns of the dynamics of surface
currents is analysed and tested for the Gulf of Finland and the south-western Baltic
Sea. These patterns are highlighted using statistical analysis of a large number of
Lagrangian trajectories constructed by using horizontal velocity fields in the uppermost layer generated by three-dimensional circulation models. The evaluation of
environmental risks and the identification of patterns of rapid Lagrangian transport
rely on a specific discretization of the direct problem of the 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 Gulf of Finland.
It is shown how the dependence of the overall ratio of net and bulk transport can be
used for highlighting the nature of the surface dynamics. Semi-persistent patterns of
net transport are identified for the Gulf of Finland using the Rossby Centre Ocean
Model (RCO) velocity fields and the offline trajectory model TRACMASS for the
time period 1987–1991. Rapid transport pathways are mostly aligned along certain
coastal segments but pathways across the gulf are evident in transitional months
(March–May and August–October). The results are applicable for estimates of the
transport of neutrally buoyant substances in the uppermost layer of the sea.
9.1 Introduction
International ship transport has dramatically increased in the Baltic Sea (Fig. 9.1)
over the last two decades. At present it accounts for up to 15 % of the world’s
cargo transportation. The largest threat to the vulnerable boreal environment of this
region is oil transportation that has increased by more than a factor of two in 2000–
T. Soomere (B)
Wave Engineering Laboratory, Institute of Cybernetics at Tallinn University of Technology,
Akadeemia tee 21, 12618 Tallinn, Estonia
e-mail: soomere@cs.ioc.ee
T. Soomere
Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
T. Soomere, E. Quak (eds.), Preventive Methods for Coastal Protection,
DOI 10.1007/978-3-319-00440-2_9,
© Springer International Publishing Switzerland 2013
283
Statistics of Lagrangian Transport Reveals
Hidden Features of Velocity Fields
Tarmo Soomere
Abstract The potential of the systematic use of Lagrangian trajectories to identify
normally hidden properties and semi-persistent patterns of the dynamics of surface
currents is analysed and tested for the Gulf of Finland and the south-western Baltic
Sea. These patterns are highlighted using statistical analysis of a large number of
Lagrangian trajectories constructed by using horizontal velocity fields in the uppermost layer generated by three-dimensional circulation models. The evaluation of
environmental risks and the identification of patterns of rapid Lagrangian transport
rely on a specific discretization of the direct problem of the 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 Gulf of Finland.
It is shown how the dependence of the overall ratio of net and bulk transport can be
used for highlighting the nature of the surface dynamics. Semi-persistent patterns of
net transport are identified for the Gulf of Finland using the Rossby Centre Ocean
Model (RCO) velocity fields and the offline trajectory model TRACMASS for the
time period 1987–1991. Rapid transport pathways are mostly aligned along certain
coastal segments but pathways across the gulf are evident in transitional months
(March–May and August–October). The results are applicable for estimates of the
transport of neutrally buoyant substances in the uppermost layer of the sea.
9.1 Introduction
International ship transport has dramatically increased in the Baltic Sea (Fig. 9.1)
over the last two decades. At present it accounts for up to 15 % of the world’s
cargo transportation. The largest threat to the vulnerable boreal environment of this
region is oil transportation that has increased by more than a factor of two in 2000–
T. Soomere (B)
Wave Engineering Laboratory, Institute of Cybernetics at Tallinn University of Technology,
Akadeemia tee 21, 12618 Tallinn, Estonia
e-mail: soomere@cs.ioc.ee
T. Soomere
Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
T. Soomere, E. Quak (eds.), Preventive Methods for Coastal Protection,
DOI 10.1007/978-3-319-00440-2_9,
© Springer International Publishing Switzerland 2013
283