A. Jankowski, Institute of Oceanology of P A S., 81-712 Sopot, Poland, e-mail: jankowsk@iopan.gda.pl
 

                                                           A b s t r a c t

Preliminary results of numerical experiments with an application of  the Princeton Ocean Model - code (cf. Blumberg
and Mellor, 1987; Mellor, 1993) to calculate wind - and density - driven circulation in the Baltic Sea are presented.
The model domain (10^o 45' E - 29^o 15' E; 53^o 50' N - 65^o 50') comprises the Baltic Sea with the Gulf of Bothnia,
the Gulf of Finland and the Gulf of Riga and was considered as closed basin. Model resolution (horizontal - 15' x 10'
i.e. about 10 Nm and vertical - 12 levels of sigma - coordinate) allow to analyse only general pattern of water
movements in the Baltic Sea.
 

Following numerical experiments were carried out:

1. Diagnostic and semi- diagnostic calculations (cf. e.g. Sarkisyan et al., 1986) - to estimate steady - state climatic
circulation for selected months (July, August, September and October) and runs were performed with POM - code
in diagnostic mode and prognostic one, subsequently.Model was forced by montly mean climatic fields of wind stress
and density.  Wind stress components were estimated by the help of standard method based on wind velocity
determined from distribution of atmospheric pressure (the multi-year averaged fields) and using relationships between
surface and geostrophic wind and square law with constant drag coefficient equal to 2.5  10^-3. Deflection angle
(counterclockwise) equal to 18^o and correction coefficient for wind velocity equal to 0.7 were applied.
Density fields were estimated by the Mamayev's simple state equation  (Mamayev, 1970) on the basis
of the multi-year averaged monthly mean fields of the sea  water temperature and salinity from Lenz (1971)
and Bock (1971) atlases for selected months.

2. Prognostic simulations for the PIDCAP period (August - October) were perfomed. As initial data for model
parameters, their values calculated in previous semi - diagnostic and diagnostic runs, were used.In these simulations
the model was forced by wind stresses and surface heat fluxes.

Heat surface fluxes and wind stresses were calculated on the basis of forcing fields available from Institue of Marine
Research, Kiel, interpolated into the model numerical grid by subroutine supplied with forcing data.Wind stress components
were estimated in similar way as in diagnostic runs with deflection angle equal to 15^o and with drag coefficient dependent
on wind velocity. Surface fluxes of sensible and latent heat were calculated by means of Launiainen's method (cf. e.g.
Launiainen, 1979: Launiainen and Vihma, 1990). Short and long wave radiation were evaluated by formulae proposed
in literature (cf. e.q. Pivovarov, 1972; Stevenson, 1982; Rozwadowska (1991).

Main attention was paid to the southeast part of the Baltic Sea, where complex bottom topography essentially influences
water movements and for that region the results of numerical simulations are presented. Hydrodynamic conditions
and variability of water exchange between the Gulf of Gdansk and the Baltic Proper along the longitudinal section
in the vicinity of the open boundary of the Gulf are also analysed.

References

Blumberg, A. F., Mellor G.L., (1987): A description of a three-dimensional coastal ocean circulation model,
[in:]  Three-Dimensional Coastal ocean Models, edited by N. Heaps, 208 pp., American Geophysical Union
Bock K.-H. (1971):  Monatskarten des Salzgehaltes der Ostsee, dargestellt fuer verschiedene Tiefenhorizonte.
Dt. hydrogr. Z., Erg.-H. R.B., No.12, Hamburg. 148 pp.
Launiainen J., (1979):  Studies of energy exchange between the air and the sea surface on the coastal area
of the Gulf of Finland. Finnish Marine Research, No. 246, 3 - 110
Launiainen J., Vihma T., (1990): Derivation of turbulent surface fluxes - an iterative flux - profile method
allowing arbitrary observing heights. Environmental Software, vol. 5, No. 3, 113 - 124
Lenz W., (1971):  Monatskarten der Temperatur der Ostsee, dargestellt fuer verschiedene Tiefenhorizonte.
Dt. hydrogr. Z., Erg.-H. R.B.,  No.11, Hamburg, 148 pp.
Mamayev O.I., (1970):  T,S - analysis of World Ocean waters. (in Russian), Gidrometeoidat, Leningrad
Mellor, G. L.,  User's guide for a three-dimensional, primitive equation, numerical ocean model, 35 pp., Prog.
in Atmos. and Ocean. Sci, Princeton University, 1993.
Pivivarov A.A., (1972): Thermology of freezing over water bodies (Termika zamerzaiushchikh vodoemov).,
Izdat. Moskovskogo Universiteta, 140 pp.(in Russian)
Rozwadowska A., (1991):  A model of solar energy input into the Baltic Sea. Studia i Mater. Oceanol., Marine
Physics 6, 223 - 242
Sarkisyan A.S., Demin Yu. L., Brekhovskikh A.L., Shakhanova T.V., (1986): Methods and results of calculation
of World Ocean circulation. Gidrometeoizdat, Leningrad, 152 pp. (in Russian)
Stevenson J.W., (1982):  Computation of heat and momentum fluxes at the sea surface during the Hawaii to Thaiti
Shuttle experiment. Joint Institute for Marine and Atmospheric Research University of Hawaii, No. 82 - 0044, 42 pp.