Eurasian autumn snow link to winter North Atlantic Oscillation is strongest for Arctic warming periods

Wegmann, Martin; Rohrer, Marco; Santolaria-Otín, María; Lohmann, Gerrit (2020). Eurasian autumn snow link to winter North Atlantic Oscillation is strongest for Arctic warming periods. Earth system dynamics, 11(2), pp. 509-524. Copernicus Publications 10.5194/esd-11-509-2020

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In recent years, many components of the connection between Eurasian autumn snow cover and win-tertime North Atlantic Oscillation (NAO) have been investigated, suggesting that November snow cover distri-bution has strong prediction power for the upcoming Northern Hemisphere winter climate. However, the non-stationarity of this relationship could impact its use for prediction routines. Here we use snow products fromlong-term reanalyses to investigate interannual and interdecadal links between autumnal snow cover and atmo-spheric conditions in winter. We find evidence for a negative NAO-like signal after November with a strongwest-to-east snow cover gradient, which is valid throughout the last 150 years. This correlation is consistentlylinked to a weak stratospheric polar vortex state. Nevertheless, decadal evolution of this link shows episodes ofdecreased correlation strength, which co-occur with episodes of low variability in the November snow index.By contrast, periods with high prediction skill for winter NAO are found in periods of high November snowvariability, which co-occur with the Arctic warming periods of the 20th century, namely the early 20th-centuryArctic warming between 1920 and 1940 and the ongoing anthropogenic global warming at the end of the 20thcentury. A strong snow dipole itself is consistently associated with reduced Barents–Kara sea ice concentration,increased Ural blocking frequency and negative temperature anomalies in eastern Eurasia.

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