ASSOCIATION BETWEEN MODES OF VARIABILITY OF JANUARY NORTHERN-HEMISPHERE SNOW COVER AND CIRCULATION

An Empirical Orthogonal Function (EOF) analysis has been applied to NO AA/NESDIS snow concentration data. The major modes of variability in J anuary Northern Hemisphere snow concentration have been extracted and analysed. The analysis was completed separately over Eurasia and North America. Strong, coherent patterns were found for each of the first t hree EOFs that were analysed over both continents. Over Eurasia the fi rst EOF showed much of Europe as well as western and central Asia in p hase but eastern Asia of the opposite phase although the signal was so mewhat weaker. North America had a very similar first EOF with a large positive anomaly centered over Montana reaching loadings of over 0.8. East of the Great Lakes, the anomaly changes sign, although again, it s magnitude is much smaller. An EOF examination was also made of the a nomalous 700 hPa geopotential height fields. These modes of variabilit y were correlated with those of snow cover with the aim of investigati ng the mechanisms by which the surface boundary snow and the overlying circulation can interact. The stronger correlations were discussed an d logical physical scenarios were presented for each. The results indi cate that there was no common pattern whereby one medium was always fo rcing the other but rather a complex array of interactions where each medium could influence the other. To support the physical basis of the relationships being depicted by the EOF study, a case study of Januar y 1981 was made. The presence of intercontinental relationships was al so investigated and such relations were strongly suggested. It was pro posed that the large scale organisation of the atmosphere between the two continents could go some way to explaining these links in snow var iability.