TY - JOUR
T1 - The skeleton of tropical intraseasonal oscillations
AU - Majda, Andrew J.
AU - Stechmann, Samuel N.
N1 - Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2009/5/26
Y1 - 2009/5/26
N2 - 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.
AB - 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.
KW - Atmospheric convection
KW - Convectively coupled equatorial waves
KW - Madden-Julian oscillation
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U2 - 10.1073/pnas.0903367106
DO - 10.1073/pnas.0903367106
M3 - Article
C2 - 19423670
AN - SCOPUS:66649137078
VL - 106
SP - 8417
EP - 8422
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 21
ER -