12 Forecasting of Sea-Ievel, Currents and
Sea Ice in the Baltic Sea
LENNART FUNKQUIST AND HANS DAHLIN
Swedish Meteorological and Hydrological Institute
12.1 Introduction
The development of operational oceanography is, and should be, driven by the
users. To satisfy user requirements scientists and maybe more often consultants are
producing the tools or systems for an operational service. Even if the needs
expressed by the users seem to be impossible to satisfy, rather modest products can
often significantly improve the knowledge on which the users base their decisions.
In many cases meteorology is serving as a model for the development of operational ocanography and existing oceanographical services are in general produced
by or in close co-operation with meteorological agencies. The existing services
today are accordingly mainly related to the interface between meteorology and
oceanography, the sea surface. Forecasts of surf ace temperature, sea ice, sea level,
surface circulation and surface drift have existed for several sea areas for a decade
or more. Several oceanographic services based on ocean forecasting exist today
also for users in the Baltic Sea area. Most of them have been developed on request
arid in co-operation with the users.
The Baltic Sea, the world's largest brackish water area, is almost totally enclosed.
Only three narrow straits around the Danish Islands connect the Baltic Proper with
the Kattegat and the World Ocean. A large drainage area gives a massive fresh
water input, which in balance with the water exchange with the North Sea creates a
horizontal salinity gradient from zero to ocean levels distributed over about 3000
km. The Baltic is almost tideless, but due to changes in air pressure and wind forcing sea level changes of up to plus or minus one meter from mean sea level are
observed. The changing sea level causes barotropic currents, which in the narrow
straits at the entrance area can reach values of several knots.
From southem Sweden and northwards, the shore is subject to continuous geological uplift with up to 8 mmlyear. Over the centuries, this has created new
islands, the change in location of many centres or whole coastal towns and the construction ofnew harbours. The seasonal and inter-annual variations ofsea-level are
also large.
The distribution of sea ice can vary from almost total ice coverage during very
strong winters to just covering inner parts of the large gulfs in mild winters. In
summer, the surface temperature reaches about 20°C.
Almost 85 million people are living in the drainage area ofthe Baltic Sea belonging to 15 countries ofwhich nine are bordering the sea. The countries have in general high-developed industry, agriculture and forestry. At least Finland and Sweden
Sea Ice in the Baltic Sea
LENNART FUNKQUIST AND HANS DAHLIN
Swedish Meteorological and Hydrological Institute
12.1 Introduction
The development of operational oceanography is, and should be, driven by the
users. To satisfy user requirements scientists and maybe more often consultants are
producing the tools or systems for an operational service. Even if the needs
expressed by the users seem to be impossible to satisfy, rather modest products can
often significantly improve the knowledge on which the users base their decisions.
In many cases meteorology is serving as a model for the development of operational ocanography and existing oceanographical services are in general produced
by or in close co-operation with meteorological agencies. The existing services
today are accordingly mainly related to the interface between meteorology and
oceanography, the sea surface. Forecasts of surf ace temperature, sea ice, sea level,
surface circulation and surface drift have existed for several sea areas for a decade
or more. Several oceanographic services based on ocean forecasting exist today
also for users in the Baltic Sea area. Most of them have been developed on request
arid in co-operation with the users.
The Baltic Sea, the world's largest brackish water area, is almost totally enclosed.
Only three narrow straits around the Danish Islands connect the Baltic Proper with
the Kattegat and the World Ocean. A large drainage area gives a massive fresh
water input, which in balance with the water exchange with the North Sea creates a
horizontal salinity gradient from zero to ocean levels distributed over about 3000
km. The Baltic is almost tideless, but due to changes in air pressure and wind forcing sea level changes of up to plus or minus one meter from mean sea level are
observed. The changing sea level causes barotropic currents, which in the narrow
straits at the entrance area can reach values of several knots.
From southem Sweden and northwards, the shore is subject to continuous geological uplift with up to 8 mmlyear. Over the centuries, this has created new
islands, the change in location of many centres or whole coastal towns and the construction ofnew harbours. The seasonal and inter-annual variations ofsea-level are
also large.
The distribution of sea ice can vary from almost total ice coverage during very
strong winters to just covering inner parts of the large gulfs in mild winters. In
summer, the surface temperature reaches about 20°C.
Almost 85 million people are living in the drainage area ofthe Baltic Sea belonging to 15 countries ofwhich nine are bordering the sea. The countries have in general high-developed industry, agriculture and forestry. At least Finland and Sweden