Department of Earth System Science

Variations in the Arctic Oscillation (AO) and its regional manifestation, the North Atlantic Oscillation (NAO), generate much of the nonseasonal variability in the winter climate over the Northern Hemisphere midlatitudes. Despite being an internal mode of the atmosphere, the Arctic and North Atlantic Oscillations (N/AO) exhibit a slightly red spectrum, varying on quasi-biennial (2-3 years) and quasi-decadal time scales. Such low-frequency variability is likely due to the coupling of the atmosphere to boundary conditions and/or external forcings. Here we show that Eurasian snow cover, particularly over eastern Siberia (ESB), exhibits quasi-biennial persistence similar to the N/AO. Furthermore, the snow-AO mechanism operates on quasi-biennial timescales, with fall ESB snow cover significantly related to vertically propagating Rossby wave activity and the N/AO for the next two to three winters. On the basis of land surface model simulations from the Global Land Data Assimilation System (GLDAS), the interseasonal carryover of ESB snow is related to soil moisture anomalies and an evaporation-convection feedback. These findings suggest quasi-biennial persistence of the N/AO is partly due to land surface forcing in the form of both ESB snow and soil moisture anomalies.