Circulation Response to Eurasian versus North American Anomalous Snow Scenarios in the Northern Hemisphere with an AGCM Coupled to a Slab Ocean Model

Abstract

he difference between snow-covered and snow-free conditions is the most climatically significant natural seasonal change the land surface can experience. Most GCM studies investigating snow?atmosphere interactions have focused on impacts of Eurasian snow anomalies caused by the magnitude of snow mass, while North American snow has been shown to have a weaker 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. The authors explore the circulation response to anomalous snow scenarios, for both North America and Eurasia, using a slab ocean model. Surface response 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 consistent through multiple levels in the lower troposphere under maximum snow conditions throughout much of the midlatitudes in both experiments during early winter. Areas of strengthened midtropospheric eddy kinetic energy correlate well with steep geopotential height gradient differences and increased zonal wind at 250 hPa over the western Pacific. Both experiments show similar atmospheric response pathways; however, circulation response to maximum Eurasian snow is focused downstream in early winter, whereas upstream response is particularly evident from the North American experiment. This paper focuses on differences as a result of Eurasian versus North American snow forcing in atmospheric circulation response using an AGCM with a slab ocean model.