Planetary- and synoptic-scale feedbacks between tropospheric and sea ice cover changes in the Arctic

Polar regions are key players in the climate system because of the strong modification of the surface energy budget through snow and ice cover, which is tightly coupled with the global circulation of the atmosphere and the ocean. The observed trend of decreasing sea ice has been attributed to a combination of natural and anthropogenic drivers. Due to the interaction of ocean, ice and atmosphere, a very complex nonlinear system is set up, where the physical mechanisms are not well understood. This is clearly shown by the IPCC AR4 model simulations that under predict the recent decline in sea ice concentration. Furthermore these models can not explain the shift to strong negative AO phases.

Our analysis is based on ERA Interim Reanalysis data known to be the most reliable source of reanalysis data at the moment. The atmospheric data are analyzed by comparing the correlation of two time slices considered as the "high ice phase" 1990-2000 and the "low ice phase" 2001-2010 with an index of sea ice concentration. The analysis includes also the computation of heat and localized Eliassen-Palm fluxes for time periods between 10-90 days and 2-6 days. A main focus is to characterize the impacts on quasi-stationary planetary waves and the synoptic scale circulation seperately. We describe physical mechanisms how the ice free parts of the Arctic Ocean in September influence the atmosphere in the following winter. Due to the additional oceanic heat source, positive atmospheric temperature anomalies occur that persist into the next winter. Our studies show a reduced vertical stability of the atmosphere and changing heat fluxes due to an earlier onset of baroclinic instability. Nonlinear feedbacks generate changes in baroclinic and planetary wave energy fluxes.

In addition to regional feedbacks between ocean, ice and atmosphere there are remote impacts on planetary waves described by changing large-scale atmospheric wave trains over the Pacific Ocean. These changes in mid latitudes deliver a clear hint that the Arctic sea ice decrease in the low ice phase triggers large scale atmospheric teleconnection patterns which could be a possible feedback for the recent shift to a negative AO phase.