Abstract : 3K.8
Spatial differences over Romania of the snow cover variability in relationship to temperature and atmospheric circulation

Liana Cazacioc
liana.cazacioc@meteo.inmh.ro
National Meteorological Administration

The basic characteristics of snow cover duration in Romania from 1961 until 1990 are described. The annual mean number and the variability index of days with snow cover in the cold season (December-March) were calculated. The spatial distribution of the monthly mean number of days with snow cover both for positive and negative NAO phase from December to March points out a large variability over Romania, due to the shape and massiveness of Carpathians Mountains.

For each month from December to March were determined the climatic frequencies of occurrence of days with snow cover. In all the winter months, the largest values were recorded in the mountain region of Romania.

The snow cover duration and temperature relationship was analysed in the winter months (December-March). The correlation coefficients between the number of days with snow cover and monthly mean temperature are mostly negative over Romanian territory.

The influence of the atmospheric circulation in the North Atlantic region on the snow cover in Romania is studied by using the NAO index and the frequency of the Hess-Brezowsky weather types. The correlation coefficients between the NAO index values and the monthly number of days with snow cover from December to March 1961-1990 are mostly negative at 99 Romanian stations. The westerly and northerly Hess-Brezowsky atmospheric circulations types were taken into consideration and their association with snow cover duration in Romania was examined. The westerly circulations lead to less snowy winter, whereas the northerly circulations increase the probability of snowy winters in Romania.

The dependency of snow cover duration with the altitude was tested by using a higher order of multiple statistical regression models. The best correlation was found in a 4th degree polynomial function, both for the months with positive and negative phase of the NAO. The relationship between snow cover and altitude is stronger in the months with positive NAO index than in the months with negative NAO index.