A Rotation Procedure to Improve Seasonally Varying Empirical Orthogonal Function Bases for MJO Indices
Abstract 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 empir...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Wiley
2022-08-01
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| Series: | Geophysical Research Letters |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2022GL099998 |
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| Summary: | Abstract 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 empirical orthogonal functions (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. |
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| ISSN: | 0094-8276 1944-8007 |