35. Orbital forcing on atmospheric dynamics during the last interglacial and glacial inception

Abstract

Large-scale atmospheric patterns are examined on orbital timescales using the ECHO-G climate model which explicitly resolves the atmosphere-ocean-sea ice dynamics. It is shown that in contrast to boreal summer where the climate follows mainly the local radiative forcing, the boreal winter climate is strongly determined by modulation of circulation modes linked to the Arctic Oscillation/North Atlantic Oscillation and the El Niño Southern Oscillation. We find that a positive phase of the Arctic Oscillation/ North Atlantic Oscillation is linked to below normal convection in the tropical Pacific. The related atmospheric circulation patterns induce nonuniform temperature anomalies, much stronger in amplitude than by the direct solar insolation. In concert with the direct solar insolation, this provides for a temperature drop over the Northern Hemisphere continents 115 000 years before present. We argue that the large-scale teleconnection pattern is important for the interpretation of proxy data as well as for the mechanisms responsible for the last interglacial, glacial inception and millennial climate variability.