Salinity
Currents Particle
driftThe Gulf of Riga Project 1993-1998, Nordic Council of Ministers
By Jüri Elken and Urmas Raudsepp
Estonian Marine Institute, Department of Marine Physics
| Results: | Salinity |
Currents |
Particle
drift |
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MODEL
3D GFDL circulation model, originally developed by Bryan and Cox and further modified by Killworth by including the free surface mode, has been applied for the Gulf of Riga. The model incorporates also the Baltic Proper and the Gulf of Finland as surrounding areas. Horizontal grid step of the model is 2 miles. Vertical grid step is 5 meters from the surface down to 130 m and larger grid steps are used below 130 m. Constant values are taken for the horizontal turbulence coefficients. Vertical diffusion coefficients are calculated by Richardson-number dependence, with constants taken to simulate the annual cycle of temperature and salinity.
INITIAL AND FORCING DATA
Modeling period starts from 1 April 1993 and covers 1 year.
Initial temperature and salinity distribution was interpolated from the Gulf of Riga hydrographic database and the HELCOM BMP data.
Freshwater input was taken into account from the monthly runoff database of the Gulf of Riga Project. Data from the SMHI runoff database were used for the remote regions. Salt fluxes in the Darss, Öresund and in the Aland Sea were taken into account as long-term mean fluxes.
Atmospheric forcing (wind and heat flux) was incorporated from the SMHI forcing database (data from coastal meteorological stations interpolated over the sea area). Local meteorological observations at Estonian weather stations (EMHI) were also used.
VALIDATION
The model has been proved able to simulate annual stratification cycle,
mesoscale flow events and thermohaline structures at the straits and response
of inflow events in the gulf interior. The model reproduces 24-h period
current oscillations in the Irbe Strait as well.
RESULTS
| SALINITY |
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a) Surface salinity
Animation contains 61 frames with 1-day interval. Period covers January-February
1994. In the end of January, saline water of the Baltic Proper is pushed
into the Gulf of Riga through the Irbe Strait due to dominating southerly
winds. After passing the Cape of Kolka, saline water turns to the south
and moves along the Latvian coast in the bottom layers. Diluted Gulf water
is moved out through the Suur (Virtsu) Strait. Less saline water is found
at the Daugava and Pärnu River mouths.
Click the picture to start animation (1047K)
| b) Inflow through the Irbe Strait, salinity section |
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Animation contains 30 frames with 1-day interval. Period covers mid-January
to mid-February 1994. Section is oriented from the west to the east, from
the Cape of Kolka through the Ruhnu Island to the Salacgriva area. During
the inflow period, at southerly winds, the saline water of the Baltic Proper
enters the Gulf between the Cape of Kolka (left side of the picture) and
the Ruhnu Island. The southward flow is concentrated in the bottom layers
of the Latvian (western) side of the passage.
Click the picture to start animation (329K)
| c) Inflow through the Suur (Virtsu) Strait, salinity section |
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Animation contains 40 frames with 1-day interval. Period covers August
1994. Section is oriented from the south to the north, from the Jurmala
area through the Ruhnu Island to the Suur (Virtsu) Strait. During the inflow
period, at northerly winds, the saline water of the Gulf of Finland entrance
enters the Gulf of Riga through the shallow strait (right side of the picture).
It further sinks to the bottom of more deep areas of the Gulf.
Click the picture to start animation (548K)
| CURRENTS |
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a) Surface currents
Animation contains 49 frames with 1-hour interval. Note that current
vectors rotate clockwise with 14-h period due to the Coriolis force. Therefore,
instantaneous currents differ very much from the mean flow.
Click the picture to start animation (698K)
| b) Bottom currents |
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Animation contains 35 frames with 1-hour interval. Note that current
vectors rotate clockwise with 14-h period due to the Coriolis force.
Click the picture to start animation (446K)
| PARTICLE DRIFT |
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Below are two examples of the bottom particle drift calculated by application
"Visriga.exe" which may ordered on the CD-ROM. In these examples, each
hour a new particle (red dot) has been introduced to the bottom layer of
the point source. Integration has been done over several months. Depending
on the actual circulation and source location, the spread pattern may vary
considerably. However, some accumulation area of the bottom particles can
be found around the Ruhnu deep. The upper panel shows clearly, how the
bottom water (and particles) moves along the deep channel between the Kolka
and Ruhnu towards greater depths in the south. The lower panel also exhibits
the southward drift tendency.
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Further questions to:
elken@phys.sea.ee
raudsepp@phys.sea.ee