The three-dimensional PM3D hydrodynamic model (Parallel Model 3D) is a version of the numerical [1] M3D model, modernized within the framework of the SatBałtyk project, which is based on the POM (Princeton Ocean Model). As a result of the parallelization of the calculations performed on computers equipped with multi-core processors and the implementation of procedures for assimilating satellite data, the PM3D enables a more accurate calculation of water temperatures and other water parameters at high resolution. Information about the weather is supplied from the UM numerical weather model (Unified Model) operating at ICM with a resolution of 4 km. Over the entire Baltic Sea the PM3D model has a resolution of 1 nautical mile (ca 1.9 km). However, this model enables the resolution to be increased for certain areas with two-way downscaling, which means that the water temperature can be calculated at a resolution of 0.5 nautical miles (ca 0.9 km) in the southern Baltic (see figure). The PM3D works operationally, assimilating incoming satellite data on SST determined from AVHRR or MODIS radiometers in cloudless regions. The model takes into account the inflow of solar radiation calculated using current satellite data from the SolRad model.

Interesting phenomena visible on temperature maps

Coastal upwelling is a current raising deep water up to the surface; such events occur in some regions of the Baltic [4]. Satellite maps of the southern shores of the Baltic often show areas with cooler surface waters, the effect of upwelling. This occurs when water from deeper layers, usually cooler, are brought to the surface under the influence of a current generated by winds blowing parallel to the coastline. In winter the temperature of upwelled waters may be higher than at the surface, so the temperature maps will show this as a warmer area. A thermal front is a transition zone separating water masses of different temperatures; the temperature gradient across such a front is therefore steep. Thermal fronts in the Baltic are variable in size and stable over time. They usually form at the boundaries between basins of different depths (all-year or seasonal), in areas subject to upwelling (short-term but with a temporally stable position), within a hydrological front, restricting the spread of waters flowing in from rivers (short-term, with frequent changes in position frequently), around eddies etc. The waters on either side of the front often differ not only in temperature but also with respect to other physicochemical features, such as salinity, transparency and other optical properties. Mesoscale eddies are disturbances in the current field resulting from anomalies of temperature, salinity and sea level on spatial scales from 10 to 100 km and durations from a few days to a month. Local structures with dimensions smaller than 10 km are defined as sub-mesoscale eddies. Eddies of various sizes in the Baltic are often seen on satellite radiometric images (e.g. in distributions of SST, chlorophyll a levels etc.) and on radar images, as sea surface disturbances.

  [1] Jędrasik J., 2005, Validation of hydrodynamic part of the ecohydrodynamic model for the southern Baltic, Oceanologia, 47(4),. 517-541 [2] Kowalewski M., Kowalewska-Kalkowska H., 2011, Performance of operationally calculated hydrodynamic forecasts during storm surges in the Pomeranian Bay and Szczecin Lagoon, Boreal Environment Research, Res. 16 (suppl. A): 27–41 [3] Kowalewski M.,1997, A three-dimensional, hydrodynamic model of the Gulf of Gdańsk; Oceanol. Stud., 26 (4); 77–98 [4] Kowalewski M., Ostrowski M., 2005, Coastal up- and downwelling in the southern Baltic, Oceanologia, 47 (4), 453–475