Associations between continental‐scale snow cover anomalies and air mass frequencies across eastern North America

The spatial extent of snow cover has been shown to affect diverse meteorological variables, including surface air temperatures, atmospheric moisture, longwave and shortwave radiation budgets, and sensible and latent heat fluxes. However, little research has directly addressed the role of snow cover extent in the production and/or maintenance of diverse air mass types. The major hypothesis of this study is that continental-scale snow cover anomalies should influence air mass frequencies because of their important effects on land-surface energy budgets. To test this hypothesis, satellitederived Northern Hemisphere snow cover data were used in conjunction with a unique air mass classification routine to ascertain the association between air mass frequencies and snow cover anomalies across eastern North America. Results indicate that continental-scale snow cover anomalies are strongly associated with changes in the frequency of air masses over eastern North America. However, strong mid-tropospheric circulation anomalies are often associated with the snow cover and air mass frequency changes, making it difficult to judge the relative importance of the snow cover anomaly to the variations in air mass frequency. During the months of November, December, January and April, circulation patterns are present that would lead to the observed snow cover anomalies and associated air mass frequency changes. Thus, we hypothesize that snow cover anomalies (resulting from the strong circulation anomalies) help to enhance changes in the air mass frequencies of the region. However, during the months of February and March no strong circulation anomalies are apparent, suggesting that during these months snow cover may play a dominant role in air mass frequency variations. Copyright  2002 Royal Meteorological Society.