16
T. Soomere
The situation for the current-induced transport is fundamentally different. The instantaneous field of currents is an integral reaction of water masses to a variety of
forcing factors such as river discharge, various air–sea interaction processes (wind
forcing, precipitation, evaporation, freezing and melting), dynamics of water masses
in remote sea areas, local mesoscale dynamics, optionally tidal forcing or long
waves, etc. Sea currents form a highly nontrivial system of motions. It is usually
highly anisotropic, inhomogeneous, non-stationary and exhibits large spatial variations even for practically stationary wind events. In semi-enclosed sea areas such as
the Baltic Sea the currents are frequently even in antiphase with wave- and windinduced transport features (Andrejev et al. 2004; Gästgifvars et al. 2006). Consequently, the probability of a vulnerable spot being hit by an oil spill (or a damaged
and drifting ship) carried by surface currents may vary largely for different areas,
even if they are located at an equal distance from this point.
In spite of fast developments concerning the 3D modelling of the marine environment, reconstruction of even surface transport of tracers is today still an extreme
challenge. There is not yet a deterministic method capable of adequately reproducing the floating object drift (Vandenbulcke et al. 2009) and even small errors
in its estimates can drastically change the calculated particle trajectories (Griffa
et al. 2004). In particular, the inadequate representation of current patterns is one
of the main reasons why the forecast of current-induced transport is usually much
less reliable compared to the description of wind- and wave-induced transport. For
this reason most of our contributions concentrate on the analysis of the role of the
current-induced transport where we see the largest unused potential for the use of
intrinsic features of marine dynamics for environmental management. Yet we still
stress the importance of the wind- and wave-induced drift and highlight their joint
impact on the seasonal variation of the location of the optimum fairway in Chap. 11.
1.10 Dynamical and Statistical Forecast
A consequence of the intrinsic complexity of the reproduction of the details of ocean
circulation is that current patterns cannot be exactly forecast today. This limits using
the simulation results in many direct applications such as the exact forecast of the
dynamics of an oil spill or of the drift of an item (ship, rescue boat, lost container,
iceberg, etc.) at sea. Yet making use of certain favourable statistical features of currents is a promising approach. It has been used, for example, in minimizing fuel
consumption along Atlantic-crossing ship routes (Lo and McCord 1998), where for
the eastbound voyages the statistical approach consistently outperformed the deterministic approach.
The importance of statistical methods and their consequences in marine design
and operation are now widely acknowledged. They are most extensively used in
studies of wave properties. Although the outcome of the statistical approach is not
always explicit, it has been extensively used to quantify and mitigate the probabilities of accidents and failures. For example, the traditional format of classification
T. Soomere
The situation for the current-induced transport is fundamentally different. The instantaneous field of currents is an integral reaction of water masses to a variety of
forcing factors such as river discharge, various air–sea interaction processes (wind
forcing, precipitation, evaporation, freezing and melting), dynamics of water masses
in remote sea areas, local mesoscale dynamics, optionally tidal forcing or long
waves, etc. Sea currents form a highly nontrivial system of motions. It is usually
highly anisotropic, inhomogeneous, non-stationary and exhibits large spatial variations even for practically stationary wind events. In semi-enclosed sea areas such as
the Baltic Sea the currents are frequently even in antiphase with wave- and windinduced transport features (Andrejev et al. 2004; Gästgifvars et al. 2006). Consequently, the probability of a vulnerable spot being hit by an oil spill (or a damaged
and drifting ship) carried by surface currents may vary largely for different areas,
even if they are located at an equal distance from this point.
In spite of fast developments concerning the 3D modelling of the marine environment, reconstruction of even surface transport of tracers is today still an extreme
challenge. There is not yet a deterministic method capable of adequately reproducing the floating object drift (Vandenbulcke et al. 2009) and even small errors
in its estimates can drastically change the calculated particle trajectories (Griffa
et al. 2004). In particular, the inadequate representation of current patterns is one
of the main reasons why the forecast of current-induced transport is usually much
less reliable compared to the description of wind- and wave-induced transport. For
this reason most of our contributions concentrate on the analysis of the role of the
current-induced transport where we see the largest unused potential for the use of
intrinsic features of marine dynamics for environmental management. Yet we still
stress the importance of the wind- and wave-induced drift and highlight their joint
impact on the seasonal variation of the location of the optimum fairway in Chap. 11.
1.10 Dynamical and Statistical Forecast
A consequence of the intrinsic complexity of the reproduction of the details of ocean
circulation is that current patterns cannot be exactly forecast today. This limits using
the simulation results in many direct applications such as the exact forecast of the
dynamics of an oil spill or of the drift of an item (ship, rescue boat, lost container,
iceberg, etc.) at sea. Yet making use of certain favourable statistical features of currents is a promising approach. It has been used, for example, in minimizing fuel
consumption along Atlantic-crossing ship routes (Lo and McCord 1998), where for
the eastbound voyages the statistical approach consistently outperformed the deterministic approach.
The importance of statistical methods and their consequences in marine design
and operation are now widely acknowledged. They are most extensively used in
studies of wave properties. Although the outcome of the statistical approach is not
always explicit, it has been extensively used to quantify and mitigate the probabilities of accidents and failures. For example, the traditional format of classification