Time–height ribbons

Two of the atmosphere's slow clocks, drawn in time and height. The quasi-biennial oscillation: equatorial stratospheric winds flip between easterly and westerly roughly every 28 months, each phase appearing aloft and descending — measured by radiosondes over Singapore since 1953. And the Northern Annular Mode by level: anomalies in the polar vortex that drip down from the stratosphere to the surface over weeks, the pattern behind many cold spells.

QBO: monthly zonal wind at 70–10 hPa from the FU Berlin / KIT Singapore series. NAM/SAM: daily ERA5 annular modes by level (Baldwin & Dunkerton 2001), σ.

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