A Rotation Procedure to Improve Seasonally Varying Empirical Orthogonal Function Bases for MJO Indices

Various indices have been defined to characterize the phase and amplitude of the Madden-Julian oscillation (MJO). One widely used index is the Outgoing Longwave Radiation (OLR) based MJO index (OMI), which is calculated using the spatial pattern of 30-96-day eastward-filtered OLR. The EOFs used to c...

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Bibliographic Details
Published in:Geophysical research letters 2022-08, Vol.49 (15), p.n/a
Main Authors: Weidman, Sarah, Kleiner, Ned, Kuang, Zhiming
Format: Article
Language:English
Subjects:
Astronomy
Empirical orthogonal functions
EOFs
Long wave radiation
Madden-Julian oscillation
Mathematical analysis
Methods
MJO
OMI
Orthogonal functions
Oscillations
Procedures
Radiation
Rotation
Weather forecasting
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Summary:Various indices have been defined to characterize the phase and amplitude of the Madden-Julian oscillation (MJO). One widely used index is the Outgoing Longwave Radiation (OLR) based MJO index (OMI), which is calculated using the spatial pattern of 30-96-day eastward-filtered OLR. The EOFs used to calculate the OMI in observations are prone to degeneracy and exhibit oscillations on the order of 10-20 days, despite initial filtering of the OLR. We propose a simple modification to the OMI that involves aligning the EOFs between neighboring days while retaining the spatial pattern described by the EOFs. This rotation method is implemented as a postprocessing procedure of the current OMI calculation and cleanly removes the spurious oscillations and degeneracy issues seen in the standard method. A similar rotation procedure can be implemented in calculations of other MJO indices.
ISSN:0094-8276
1944-8007
DOI:10.1029/2022GL099998