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Changes in meandering of the Northern Hemisphere circulation

Proposes a novel meandering index which captures the maximum waviness in geopotential height contours at any given day, using all information of the full spatial position of each contour
Analyzes data on different time scale (from daily to 11 day running means) and both on hemispheric and regional scales
Analyzes how seasonal distributions of this index have changed over 1979–2015
Detects that the most robust changes are for autumn which has seen a pronounced increase in strongly meandering patterns at the hemispheric level as well as over the Eurasian sector
In contrast, the data shows significant downward trends in meandering in summer for both the hemisphere and the Eurasian sector on daily timescales, which is consistent with the recently reported decrease in summer storm track activity
Finds that the American sector shows the strongest increase in meandering in the warm season: in particular for 11 day running mean data, indicating enhanced amplitudes of quasi-stationary waves
The findings have implications for both the occurrence of recent cold spells and persistent heat waves in the mid-latitudes

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