Circulation response to North American versus Eurasian anomalous snow scenarios in the Northern Hemisphere with an AGCM coupled to a slab ocean model

The difference between snow-covered versus snow-free conditions is the most climatically significant natural, seasonal change the land surface can experience. Numerous studies to date have investigated the implications of snow forcing the atmosphere, however the cause and effect relationship has not been decisively demonstrated from observed data alone. Most GCM studies investigating snow-atmosphere interactions have focused on impacts of Eurasian snow anomalies due to the magnitude of snowmass, however North American snow has been shown to have a weak relationship with downstream climate. Experiment design of recent snow-atmosphere interactions studies has been limited to atmosphere only models, with sea surface temperature (SST) and sea ice extent represented as boundary conditions, based on climatological values. We explore the circulation response to anomalous snow extent and depth scenarios, for both North America and Eurasia, using data-driven and slab ocean models. Anomalous snow scenarios are based on 1967-1995 observed snow data. Surface and atmospheric response to anomalous snow is greater both in magnitude and spatial extent under slab ocean conditions. Surface response results include significant SST cooling directly downstream of each individual forcing region in addition to upstream centers of remote cooling under maximum snow conditions. Atmospheric response to anomalous snow conditions is dominated by a barotropic response under maximum snow conditions throughout much of the mid latitudes in both experiments during early winter. Areas of strengthened mid-tropospheric eddy kinetic energy correlate well with steep geopotential height gradient differences and increased zonal wind at 250 hPa over the western Pacific in both experiments. Both Eurasian and North American experiments show similar atmospheric pathways, however circulation response to maximum Eurasian snow is focused downstream in early winter for both slab ocean and data-driven experiments, whereas upstream response is particularly evident from the North American slab ocean experiment. This paper focuses on differences as a result of Eurasian versus North American snow forcing in atmospheric circulation response using an AGCM with slab ocean model.