Increases in Northern Hemisphere winter circulation waviness over 1989 to 2011 driven by decadal oceanic variability.

Wintertime waviness in Northern Hemisphere midlatitudes increased from 1989 to 2011, and sea surface temperature and sea ice variability explains about 48.7 to 63.3% of the observed rise.

• Why it matters: The mechanism behind the winter waviness trend is unresolved, and prior hypotheses linking Arctic amplification to jet weakening have not been supported.
• What they did: Using large-ensemble simulations plus statistical and dynamical diagnostics, the study attributes roughly half to two-thirds of the increase to sea surface temperature and sea ice variability, with the AMO’s positive phase as the main driver.
• The result: The AMO enhances waviness across northern Eurasia, the northwest Pacific, and the North Atlantic, while a negative Interdecadal Pacific Oscillation shift partially offsets effects in the northwest Pacific; near-term uncertainty is dominated by internal variability.

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