The governing thermodynamics of the Madden‐Julian Oscillation (MJO) is examined using sounding and reanalysis data. On the basis of four objective criteria, results suggest that the MJO behaves like a moisture mode–a system whose thermodynamics is governed by moisture–only over the Indian Ocean. Over this basin, the MJO shows a slow convective adjustment timescale, its zonal scale is smaller, and it exhibits slow propagation, allowing moisture modes to exist. Elsewhere, the faster‐propagating wavenumber 1–2 components are more prominent preventing weak temperature gradient (WTG) balance to be established. As a result, temperature and moisture play similar roles in the MJO's thermodynamics outside the Indian Ocean.
The eastward propagation of the Madden‐Julian oscillation (MJO) is known to hinge crucially on the effects of horizontal moisture advection, which involve two main types of circulation anomalies. The first are those of the MJO itself, while the second are those of embedded Rossby‐type “eddies,” which tend to be most active to the west of the MJO's convective center. To quantify the relative importance of the eddies, a novel approach is taken in which their formal definition is given by the residual of a least‐squares fit to an observed bivariate MJO index. Results show that the eddies, when defined in this way, are generally of leading importance for fostering the MJO's eastward propagation in terms of column‐integrated moisture. The picture is seen to be reversed, however, when using a traditional filter‐based method to define the eddies, which are then strictly “high‐frequency” in nature.
more » « less- Award ID(s):
- 1839741
- PAR ID:
- 10427965
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 13
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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