The leading statistical mode of winter climate variability for the extratropical Northern Hemisphere, a same-signed height anomaly stretched across the polar cap and an opposite-signed anomaly centered over the respective ocean basins of the mid-latitudes, has received much attention from the science community. Research continues to demonstrate its importance to interannual signals and trends in climate variability and that it does not appear to be related to ENSO. A relationship has been demonstrated between this dominant mode in winter and seasonal snow cover at high latitudes in the fall. Analysis of height anomalies around the polar cap demonstrate that the genesis of the dominant winter climate mode involves coupling between the stratosphere and the troposphere. Moreover, stratosphere troposphere coupling is initiated by variability in the Eliassen-Palm (EP) flux at mid- to high-latitudes. This project will develop and expand our concept that the pattern associated with the dominant winter mode of variability for the Northern Hemisphere results from interactions among the different components of the land atmosphere climate system at high-latitudes. The team will investigate how the pattern can be forced, both locally and remotely, by boundary perturbations, through observational analysis and numerical modeling experiments of varying complexity. Though a statistically significant relationship can be shown between seasonal snow cover, the EP flux and polar cap heights, what remains unclear is the atmospheric bridge that connects the snow cover forcing and the EP flux and polar cap response, which are separated in time by a month or more. The emphasis of the research will be on the time interval that spans the snow cover advance in October and the major EP flux pulse during the early winter. Hypotheses are presented for the long lead-lag and a series of GCM experiments will test each hypothesis. Furthermore GCM experiments are proposed to test whether snow cover is an active driver of stratosphere-troposphere coupling or rather a passive leading indicator, itself a common response to forcing from the atmosphere or some other boundary forcing.
