The skeleton of tropical intraseasonal oscillations

Andrew J. Majda, Samuel N. Stechmann

Research output: Contribution to journalArticlepeer-review

Abstract

The Madden-Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. Despite the primary importance of the MJO and the decades of research progress since its original discovery, a generally accepted theory for its essential mechanisms has remained elusive. Here, we present a minimal dynamical model for the MJO that recovers robustly its fundamental features (i.e., its "skeleton") on intraseasonal/planetary scales: (i) the peculiar dispersion relation of d?/dk ≈ 0, (ii) the slow phase speed of ≈5 m/s, and (iii) the horizontal quadrupole vortex structure. This is accomplished here in a model that is neutrally stable on planetary scales; i.e., it is tacitly assumed that the primary instabilities occur on synoptic scales. The key premise of the model is that modulations of synoptic scale wave activity are induced by low-level moisture preconditioning on planetary scales, and they drive the "skeleton" of the MJO through modulated heating. The "muscle" of the MJO-including tilts, vertical structure, etc. - is contributed by other potential upscale transport effects from the synoptic scales.

Original languageEnglish (US)
Pages (from-to)8417-8422
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume106
Issue number21
DOIs
StatePublished - May 26 2009

Keywords

  • Atmospheric convection
  • Convectively coupled equatorial waves
  • Madden-Julian oscillation

ASJC Scopus subject areas

  • General

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