184
K. Myrberg and T. Soomere
This leads us to a topic of specific importance—the balance between windinduced motions, thermohaline circulation, the overall circulation pattern and water exchange properties. The results gained from the modern observations of currents and measured time series of currents in the Gulf of Finland are discussed very
shortly, only in the context of their use for the verification and validation of basinscale models. We intentionally skip several aspects of the physical oceanography of
this water body (such as surface wave climatology, marine optics, most applications
of remote sensing) and only concentrate on processes that are customarily accounted
for or parameterized in contemporary circulation models, or may substantially affect
the accuracy of their outcome. The reader is referred to Wulff et al. (2001), Feistel
et al. (2008), Dera and Wozniak (2010) for further information and references about
these processes in the entire Baltic Sea.
The importance of such a focus on a selection of features becomes clear from
the following pair of coupled questions: (i) what new information have we learned
about the circulation in the gulf during the last decades via numerical simulations,
and (ii) how much of this information is reliable and to which extent can the details
and processes in the Gulf of Finland and its interaction with the rest of the Baltic
Sea be investigated using numerical modelling tools?
More generally, the ever increasing challenge for marine scientists is to distinguish which features highlighted by the model reflect the reality and which ones are
implicitly built-in artefacts of the numerical scheme and gaps in the forcing patterns.
There are definitely areas where numerical models cannot be replaced by real measurements and where the results, even if not exact, are unrivalled. Today’s models
are definitely able to recognize to which extent the circulation in the gulf is a local
feature and how much of it is just a reflection of the open Baltic Sea conditions, or to
provide sensible estimates of the water exchange between the gulf and the Northern
Gotland Basin.
The modelling exercises have improved our understanding of the structure of the
mean circulation, its stability and the role of various driving forces in different time
scales. These issues serve as basic agents for transport and mixing. In addition, we
have learned that the current dynamics in the very thin upper layer of a few metres
may dramatically differ from that below: i.e., the cyclonic, relatively stable general
circulation in the lower layers is in some cases reversed into an anticyclonic gyre
in the uppermost water layer (Soomere et al. 2011a). Even if this feature is not perfectly quantified by the model, it is consistent with known theoretical solutions for
the circulation patterns in a stratified medium and the structure of the local forcing,
and is supported by some measurements (Suursaar 2010). For being fully convinced,
however, this feature should be verified in situ.
For many environmental problems it is important to know the residence time of
the water. This is a complicated topic which can be studied only by using modelling
tools because measurements can only give very rough estimates of its basic features.
A major development during the latter decade is that the new generation of highresolution numerical models allows us to study the mesoscale features of circulation
and, if not yet to resolve these scales in detail, at least to adequately replicate the
statistics of their impact on the circulation and transport.
K. Myrberg and T. Soomere
This leads us to a topic of specific importance—the balance between windinduced motions, thermohaline circulation, the overall circulation pattern and water exchange properties. The results gained from the modern observations of currents and measured time series of currents in the Gulf of Finland are discussed very
shortly, only in the context of their use for the verification and validation of basinscale models. We intentionally skip several aspects of the physical oceanography of
this water body (such as surface wave climatology, marine optics, most applications
of remote sensing) and only concentrate on processes that are customarily accounted
for or parameterized in contemporary circulation models, or may substantially affect
the accuracy of their outcome. The reader is referred to Wulff et al. (2001), Feistel
et al. (2008), Dera and Wozniak (2010) for further information and references about
these processes in the entire Baltic Sea.
The importance of such a focus on a selection of features becomes clear from
the following pair of coupled questions: (i) what new information have we learned
about the circulation in the gulf during the last decades via numerical simulations,
and (ii) how much of this information is reliable and to which extent can the details
and processes in the Gulf of Finland and its interaction with the rest of the Baltic
Sea be investigated using numerical modelling tools?
More generally, the ever increasing challenge for marine scientists is to distinguish which features highlighted by the model reflect the reality and which ones are
implicitly built-in artefacts of the numerical scheme and gaps in the forcing patterns.
There are definitely areas where numerical models cannot be replaced by real measurements and where the results, even if not exact, are unrivalled. Today’s models
are definitely able to recognize to which extent the circulation in the gulf is a local
feature and how much of it is just a reflection of the open Baltic Sea conditions, or to
provide sensible estimates of the water exchange between the gulf and the Northern
Gotland Basin.
The modelling exercises have improved our understanding of the structure of the
mean circulation, its stability and the role of various driving forces in different time
scales. These issues serve as basic agents for transport and mixing. In addition, we
have learned that the current dynamics in the very thin upper layer of a few metres
may dramatically differ from that below: i.e., the cyclonic, relatively stable general
circulation in the lower layers is in some cases reversed into an anticyclonic gyre
in the uppermost water layer (Soomere et al. 2011a). Even if this feature is not perfectly quantified by the model, it is consistent with known theoretical solutions for
the circulation patterns in a stratified medium and the structure of the local forcing,
and is supported by some measurements (Suursaar 2010). For being fully convinced,
however, this feature should be verified in situ.
For many environmental problems it is important to know the residence time of
the water. This is a complicated topic which can be studied only by using modelling
tools because measurements can only give very rough estimates of its basic features.
A major development during the latter decade is that the new generation of highresolution numerical models allows us to study the mesoscale features of circulation
and, if not yet to resolve these scales in detail, at least to adequately replicate the
statistics of their impact on the circulation and transport.