1. Institute of Polar Sciences, National Research Council, Trieste, Italy; Alpine-Adriatic Meteorological Society, Udine, Italy; formerly at the Deparmtent of Mathematics and Geosciences, University of Trieste, Trieste, Italy
2. Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy
3. Institute of Polar Sciences, National Research Council, Trieste, Italy; Alpine-Adriatic Meteorological Society, Udine, Italy