Synoptic-Scale Influences of Snow Cover and Sea Ice

Abstract

Daily observational data for thirty winters (1951?80) are used to test the hypothesis that anomalous distributions of snow and ice cover influence the intensification and/or trajectories of synoptic-scale cyclones. The pools of objectively chosen cases include 100 wintertime cyclonic events in the marginal snow/ice zones of each of three regions: eastern North America, the North Atlantic Ocean and the North Pacific Ocean. For each region, the errors of 24- and 48-hour force derived from a barotropic model, from persistence and from an objective analog procedure are stratified according to the concurrent anomalies of snow or ice cover. The results support the notion that the enhanced baroclinicity new the snow/ice margin contributes to stronger intensification and/or to motion parallel to the snow or ice margin in eastern North America and in the North Atlantic. A weaker signal is found in the North Pacific. The signal is qualitatively similar in the fields of 500 mb geopotential and sea level pressure, although the differences between the composites are statistically significant only in the sea level pressure fields. The results suggest that forecasts of weekly or monthly circulation patterns may, in situations of extreme snow/ice cover, be improved by consideration of observed snow/ice anomalies, if these anomalies persist through the forecast period. Controlled experiments with the NCAR (National Center for Atmospheric Research) primitive equations forecast model show a weaker dependence on the extent of snow and ice, although qualitative similarities to the data-based results are detectable.