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Testing the Hypothesis that the MJO is a Mixed Rossby-Gravity Wave Packet

Yang, Da and Ingersoll, Andrew P. (2011) Testing the Hypothesis that the MJO is a Mixed Rossby-Gravity Wave Packet. Journal of the Atmospheric Sciences, 68 (2). pp. 226-239. ISSN 0022-4928.

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The Madden Julian oscillation (MJO), also known as the intraseasonal oscillation (ISO), is a planetary-scale mode of variation in the tropical Indian and western Pacific Oceans. Basic questions about the MJO are why it propagates eastward at ~5 m s^(-1), why it lasts for intraseasonal time scales, and how it interacts with the fine structure that is embedded in it. This study will test the hypothesis that the MJO is not a wave but a wave packet-the interference pattern produced by a narrow frequency band of mixed Rossby gravity (MRG) waves. As such, the MJO would propagate with the MRG group velocity, which is eastward at ~5 m s^(-1) Simulation with a 3D model shows that MRG waves can be forced independently by relatively short-lived, eastward- and westward-moving disturbances, and the MRG wave packet can last long enough to form the intraseasonal variability. This hypothesis is consistent with the view that the MJO is episodic, with an irregular time interval between events rather than a periodic oscillation. The packet is defined as the horizontally smoothed variance of the MRG wave-the rectified MRG wave, which has features in common with the MJO. The two-dimensional Fourier analysis of the NOAA outgoing longwave radiation (OLR) dataset herein indicates that there is a statistically significant correlation between the MJO amplitude and wave packets of MRG waves but not equatorial Rossby waves or Kelvin waves, which are derived from the Matsuno shallow water theory. However, the biggest absolute value of the correlation coefficient is only 0.21, indicating that the wave packet hypothesis explains only a small fraction of the variance of the MJO in the OLR data.

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Ingersoll, Andrew P.0000-0002-2035-9198
Additional Information:© 2011 American Meteorological Society. Manuscript received 25 May 2010, in final form 24 September 2010. We thank Dr. Duane Waliser for useful comments and suggestions. This research was supported by the Geological and Planetary Sciences Davidow Fund of the California Institute of Technology.
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Caltech Davidow FundUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20110330-084638238
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23171
Deposited By: Tony Diaz
Deposited On:30 Mar 2011 20:56
Last Modified:03 Oct 2019 02:44

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