Chapter 8
Evaluation and Tuning of Model Trajectories
and Spreading Rates in the Baltic Sea Using
Surface Drifter Observations
Joakim Kjellsson, Kristofer Döös, and Tarmo Soomere
Abstract Results from experiments with surface drifters in the Baltic Sea in 2010–
2011 are presented and discussed. In a first experiment, 12 SVP-B (Surface Velocity
Program, with Barometer) drifters with a drogue at 12–18 m depth were deployed
in the Baltic Sea. In a second experiment, shallow drifters extending to a depth
of 1.5 m were deployed in the Gulf of Finland. Results from the SVP-B drifter
experiment are compared to results from a regional ocean model and a trajectory
code. Differences between the observed SVP-B drifters and simulated drifters are
found for absolute dispersion (i.e., squared displacement from initial position) and
relative dispersion (i.e., squared distance between two initially paired drifters). The
former is somewhat underestimated since the simulated currents are neither as fast
nor as variable as those observed. The latter is underestimated both due to the abovementioned reasons and due to the resolution of the ocean model.
For the shallower drifters, spreading in the upper 1–2 m of the Gulf of Finland
is investigated. The spreading rate is about 200 m/day for separations <0.5 km,
500 m/day for separations below 1 km and in the range of 0.5–3 km/day for separations in the range of 1–4 km. The spreading rate does not follow Richardson’s
law. The initial spreading, up to a distance of about d = 100–150 m, is governed
by the power law d ∼ t 0.27 whereas for larger separations the distance increases as
d ∼ t 2.5 .
J. Kjellsson (B) · K. Döös
Department of Meteorology, Bolin Centre for Climate Research, Stockholm University, Svante
Arrhenius väg 16C, 106 91 Stockholm, Sweden
e-mail: joakim@misu.su.se
K. Döös
e-mail: doos@misu.su.se
T. Soomere
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_8,
© Springer International Publishing Switzerland 2013
251
Evaluation and Tuning of Model Trajectories
and Spreading Rates in the Baltic Sea Using
Surface Drifter Observations
Joakim Kjellsson, Kristofer Döös, and Tarmo Soomere
Abstract Results from experiments with surface drifters in the Baltic Sea in 2010–
2011 are presented and discussed. In a first experiment, 12 SVP-B (Surface Velocity
Program, with Barometer) drifters with a drogue at 12–18 m depth were deployed
in the Baltic Sea. In a second experiment, shallow drifters extending to a depth
of 1.5 m were deployed in the Gulf of Finland. Results from the SVP-B drifter
experiment are compared to results from a regional ocean model and a trajectory
code. Differences between the observed SVP-B drifters and simulated drifters are
found for absolute dispersion (i.e., squared displacement from initial position) and
relative dispersion (i.e., squared distance between two initially paired drifters). The
former is somewhat underestimated since the simulated currents are neither as fast
nor as variable as those observed. The latter is underestimated both due to the abovementioned reasons and due to the resolution of the ocean model.
For the shallower drifters, spreading in the upper 1–2 m of the Gulf of Finland
is investigated. The spreading rate is about 200 m/day for separations <0.5 km,
500 m/day for separations below 1 km and in the range of 0.5–3 km/day for separations in the range of 1–4 km. The spreading rate does not follow Richardson’s
law. The initial spreading, up to a distance of about d = 100–150 m, is governed
by the power law d ∼ t 0.27 whereas for larger separations the distance increases as
d ∼ t 2.5 .
J. Kjellsson (B) · K. Döös
Department of Meteorology, Bolin Centre for Climate Research, Stockholm University, Svante
Arrhenius väg 16C, 106 91 Stockholm, Sweden
e-mail: joakim@misu.su.se
K. Döös
e-mail: doos@misu.su.se
T. Soomere
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_8,
© Springer International Publishing Switzerland 2013
251