Abstract
The governing thermodynamics of the Madden-Julian Oscillation (MJO) are
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 small effective gross moist
stability, i.e., a slow moist static energy (MSE) export by convection,
and slow convective adjustment timescale allows moisture modes to exist
for all zonal wavenumbers except 1. Elsewhere, the faster-propagating
wavenumber 1-2 components are more prominent and the effective gross
moist stability is higher, preventing weak temperature gradient (WTG)
balance to be established and causing temperature and moisture to play
similar roles in the MJO’s thermodynamics.