Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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A 10 Years Simulations of the Baltic Sea Hydrography With Special
Attention to the Sea Level Fluctuations
Kai Myrberg 1 , Oleg Andrejev 1 and Björn Sjöberg 2
1 Finnish Institute of Marine Research, P.O. Box 33, 00931 Helsinki, Finland. myrberg@fimr.fi
2 Swedish Meteorological and Hydrological Institute, Nya Varvet 31, 426 71, Västra Frölunda, Sweden.
1. Introduction
Many modeling studies have been devoted during the last
years to study long-term energy and water balance of the
Baltic with various aspects under the BALTEXprogramme
and also in different other projects (see. e.g.
Lehmann and Hinrichnsen, 2000, Meier, 2002, Omstedt
and Axell, 2003). In this study a three-dimensional
baroclinic prognostic model of the Baltic Sea (Andrejev
and Sokolov, 1989, Myrberg and Andrejev 2003,
Andrejev et al. 2004a, Andrejev et al. 2004b) is applied
to study the sea-level variability in the Baltic Sea. The
model results are compared with observed sea-levels at
numerous stations. The model results for salinity and
temperature are also compared with the observations of a
few Baltic monitoring stations. Also the results of salinity
and sea-level simulations during major inflow in 1993
are shortly discussed.
2. The model simulations
A baroclinic prognostic model of the Baltic Sea
(Andrejev and Sokolov, 1989, Myrberg and Andrejev
2003, Andrejev et al. 2004a, Andrejev et al. 2004b) with
a horizontal resolution of 2 nautical miles and 40 vertical
levels was used to simulate the hydrography of the Baltic
for a 10-years period (1991-2000). The open boundary of
the model is placed across the northern Kattegat where
sea-levels observed in Göteborg and Fredrikshamn are
given at 3h hour intervals. The model is forced by the
SMHI meteorological data with a spatial resolution of
1*1 degree. The monthly mean values of river discharges
for 1970-1990 (Bergström and Carlsson, 1994) were
used. The initial temperature and salinity fields were
assembled using a data assimilation system due to
Sokolov et al. (1997) which in turn is coupled to a Baltic
environment database (Wulff and Rahm, 1991). The spinup
period of the model was from 1 June 1990 to
December 31, 1990.
3. Main results
At first the results of the simulations were compared with
the observations of a few Baltic monitoring stations (BY-
5, BY-15, BY-31 and NB1). The comparisons showed
that the model can well reproduce the long-term main
changes of temperature and salinity but some problems
are found which might be coupled with inaccuracies in
the meteorological forcing, parameterization of the
vertical turbulence etc.
Special attention is given to the comparison of calculated
and observed sea-levels (see Fig.1). Observations from
many stations along the Baltic coast were chosen for this
purpose. The model reproduced the sea-level fluctuation
with relatively good accuracy. Nevertheless periods of
disagreement between the calculated and observed sea
level occur sometimes. Such factors as the
parameterization of the water exchange between the
Baltic and the North seas (including that the resolution of
the model 2 nm is most probably not high enough) and
the accuracy of the meteorological forcing play an
important role in the accuracy of the results. A statistical
analysis is shown to explain the discrepancies between
the observations and the model results in detail.
A special simulation was carried out to study the Baltic
major inflow in 1993. In the presentation it will be shown
(see also Fig.2.) that the model reproduce well the inflow
event and related changes in sea-levels and salinity as
well as the penetration of the saline water into the Baltic
Sea. A total volume of about 295-340 km 3 of inflowing
water could be estimated by the model being close to the
observed values.
Figure 1. Time-evolution (days) of the sea-level at
Helsinki station during January 1- April, 30 1992. The
observations are marked with a blue line whereas the
model results are marked with a red line.
Figure 2. The sea-level in Landsort for the period
December 1, 1992 to January 31, 1993.