Downward Migration of the Zonal-Mean Circulation in the Tropical Atmosphere

Kevin DallaSanta, Edwin P. Gerber

Research output: Contribution to journalArticlepeer-review


The annular modes of the extratropical atmosphere have received much attention for quantifying variability of the jet streams and storm tracks, despite the fact that the midlatitude circulation itself does not vary uniformly with longitude. While tropical fluctuations in geopotential height have lower amplitude than in the extratropics, they exhibit stronger zonal coherence, or dynamical annularity. A simple index is developed to characterize zonal-mean anomalies of the tropical circulation. It reveals that anomalies in geopotential height and zonal wind migrate downward from the upper troposphere to the surface on a time scale of about 10 days. These features are distinguishable from known modes of tropical variability, the Madden-Julian Oscillation in particular. Evidence from reanalysis and idealized model experiments confirms that this downward migration is quite generic and driven by mechanically forced variations in the strength of the Hadley circulation on subseasonal time scales.

Original languageEnglish (US)
Article numbere2020GL088084
JournalGeophysical Research Letters
Issue number18
StatePublished - Sep 28 2020


  • annular modes
  • atmospheric dynamics
  • tropical dynamics

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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