A synoptic view of the onset of the midlatitude QBO signal

Vered Silverman, Sandro W. Lubis, Nili Harnik, Katja Matthes

Research output: Contribution to journalArticlepeer-review

Abstract

The extratropical effect of the quasi-biennial oscillation (QBO), known as the Holton-Tan effect, is manifest as a weaker, warmer winter Arctic polar vortex during the east QBO phase. While previous studies have shown that the extratropical QBO signal is caused by the modified propagation of planetary waves in the stratosphere, the mechanism dominating the onset and seasonal development of the Holton-Tan effects remains unclear. Here, the governing wave-mean flow dynamics of the early winter extratropical QBO signal onset and its reversibility is investigated on a synoptic time scale with a finite-amplitude diagnostic using reanalysis and a chemistry-climate model. The extratropical QBO signal onset in October is found to primarily result from modulated stratospheric life cycles of wave pulses entering the stratosphere from the troposphere, rather than from a modulation of their tropospheric wave source. A comprehensive analysis of the wave activity budget during fall, when the stratospheric winter polar vortex starts forming and waves start propagating up into the stratosphere, shows significant differences. During the east QBO phase, the deceleration of the mid-high-latitude stratospheric zonal-mean jet by the upward-propagating wave pulses is less reversible, due to stronger dissipation processes, while during the west phase, a more reversible deceleration of the main polar vortex is found owing to the waves being dissipated at lower latitudes, accompanied by a weak but different response of the tropospheric subtropical jet. From this synoptic wave-event viewpoint, the early season onset of the Holton-Tan effect results from the cumulative effect of the QBO dependent wave-induced deceleration during the life cycle of individual upward wave pulses.

Original languageEnglish
Pages (from-to)3759-3780
Number of pages22
JournalJournals of the Atmospheric Sciences
Volume78
Issue number12
DOIs
StatePublished - Nov 2021

Keywords

  • Eddies
  • General circulation models
  • Mixing
  • Planetary waves
  • Potential vorticity
  • Quasibiennial oscillation
  • Reanalysis data
  • Rossby waves
  • Stratosphere
  • Stratosphere-troposphere coupling
  • Stratospheric circulation
  • Synoptic-scale processes
  • Teleconnections
  • Wave breaking

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