9 Statistics of Lagrangian Transport Reveals Hidden Features of Velocity Fields
295
when a tracked particle reaches the coast) and particle age (also residence time, understood here as the time elapsed from the release until the first coastal hit) in the
Gulf of Finland (Soomere et al. 2010, 2011a) described in Chaps. 10 11. These years
were quite typical in terms of wave intensity (Broman et al. 2006) and thus also in
terms of energy supply to water masses.
The velocity data used in these studies were calculated by the Rossby Centre
Ocean Model (RCO) for the entire Baltic Sea. As this model and the corresponding
forcing are described in detail in Chap. 4, only the basic information is provided
here for convenience. The RCO model is a Bryan–Cox–Semtner primitive equation
circulation model following (Webb et al. 1997) with a free surface (Killworth et al.
1991) and open boundary conditions (Stevens 1991) in the northern Kattegat. It is
coupled to a Hibler-type sea ice model (Hibler 1979) with elastic-viscous-plastic
rheology (Hunke and Dukowicz 1997). Subgrid-scale mixing is parameterized using a turbulence closure scheme of the k–ε type with flux boundary conditions to
include the effect of an enhanced layer of turbulence due to breaking surface gravity
waves (Meier 2001). A flux-corrected, monotonicity-preserving transport scheme
following (Gerdes et al. 1991) is embedded. No explicit horizontal diffusion is applied.
The horizontal resolution of the model grid is 2 × 2 nm and the model uses 41
vertical levels in z-coordinates. The thickness of the vertical layers varies between
3 m close to the surface and 12 m in 250 m depth. The model run, data from which is
used in Viikmäe et al. (2010), Soomere et al. (2011a) is forced with 10 m wind, 2 m
air temperature, 2 m specific humidity, precipitation, total cloudiness and sea level
pressure fields from a regionalization of the ERA-40 reanalysis over Europe using
a regional atmosphere model with a horizontal resolution of 25 km during 1961–
2007 (Höglund et al. 2009; Samuelsson et al. 2011). It also accounts for river inflow
and water exchange through the Danish Straits. As the atmospheric model tends to
underestimate wind speed extremes, the wind is adjusted using simulated gustiness
to improve the wind statistics (Höglund et al. 2009). Standard bulk formulae are
used to calculate the air–sea fluxes over open water and over sea ice. For further
details of the model set-up and an extensive validation of the model output the reader
is referred to Meier (2001, 2007), Meier et al. (2003).
Given the very small values of the baroclinic Rossby radius in the Gulf of Finland
(typically 2–4 km, Alenius et al. 2003), the RCO model apparently resolves a certain
part of the mesoscale dynamics in this gulf but an exact representation of the location
and properties of single eddies cannot be expected. In other words, models with this
resolution are barely eddy-permitting in this basin (cf. Andrejev et al. 2010, 2011).
The barotropic time step was 15 s and the baroclinic time step 150 s. In order to
keep the velocity data set within a reasonable limit, the model output was saved
once in 6 hours. Therefore, the simulations resolved inertial oscillations in the gulf
but owing to the coarse temporal resolution of saved data (about 1/2 of the period of
inertial oscillations at the latitude of the Gulf of Finland) these oscillations are not
resolved in the drift of particles (Chap. 8).
295
when a tracked particle reaches the coast) and particle age (also residence time, understood here as the time elapsed from the release until the first coastal hit) in the
Gulf of Finland (Soomere et al. 2010, 2011a) described in Chaps. 10 11. These years
were quite typical in terms of wave intensity (Broman et al. 2006) and thus also in
terms of energy supply to water masses.
The velocity data used in these studies were calculated by the Rossby Centre
Ocean Model (RCO) for the entire Baltic Sea. As this model and the corresponding
forcing are described in detail in Chap. 4, only the basic information is provided
here for convenience. The RCO model is a Bryan–Cox–Semtner primitive equation
circulation model following (Webb et al. 1997) with a free surface (Killworth et al.
1991) and open boundary conditions (Stevens 1991) in the northern Kattegat. It is
coupled to a Hibler-type sea ice model (Hibler 1979) with elastic-viscous-plastic
rheology (Hunke and Dukowicz 1997). Subgrid-scale mixing is parameterized using a turbulence closure scheme of the k–ε type with flux boundary conditions to
include the effect of an enhanced layer of turbulence due to breaking surface gravity
waves (Meier 2001). A flux-corrected, monotonicity-preserving transport scheme
following (Gerdes et al. 1991) is embedded. No explicit horizontal diffusion is applied.
The horizontal resolution of the model grid is 2 × 2 nm and the model uses 41
vertical levels in z-coordinates. The thickness of the vertical layers varies between
3 m close to the surface and 12 m in 250 m depth. The model run, data from which is
used in Viikmäe et al. (2010), Soomere et al. (2011a) is forced with 10 m wind, 2 m
air temperature, 2 m specific humidity, precipitation, total cloudiness and sea level
pressure fields from a regionalization of the ERA-40 reanalysis over Europe using
a regional atmosphere model with a horizontal resolution of 25 km during 1961–
2007 (Höglund et al. 2009; Samuelsson et al. 2011). It also accounts for river inflow
and water exchange through the Danish Straits. As the atmospheric model tends to
underestimate wind speed extremes, the wind is adjusted using simulated gustiness
to improve the wind statistics (Höglund et al. 2009). Standard bulk formulae are
used to calculate the air–sea fluxes over open water and over sea ice. For further
details of the model set-up and an extensive validation of the model output the reader
is referred to Meier (2001, 2007), Meier et al. (2003).
Given the very small values of the baroclinic Rossby radius in the Gulf of Finland
(typically 2–4 km, Alenius et al. 2003), the RCO model apparently resolves a certain
part of the mesoscale dynamics in this gulf but an exact representation of the location
and properties of single eddies cannot be expected. In other words, models with this
resolution are barely eddy-permitting in this basin (cf. Andrejev et al. 2010, 2011).
The barotropic time step was 15 s and the baroclinic time step 150 s. In order to
keep the velocity data set within a reasonable limit, the model output was saved
once in 6 hours. Therefore, the simulations resolved inertial oscillations in the gulf
but owing to the coarse temporal resolution of saved data (about 1/2 of the period of
inertial oscillations at the latitude of the Gulf of Finland) these oscillations are not
resolved in the drift of particles (Chap. 8).