MJO Initiation Westward Shifted and Propagation Blocked under Indian
Ocean Basin Warming during Boreal Summer
Abstract
The Madden-Julian Oscillation (MJO) exhibits evident interannual
variations, which have been mostly attributed to modulations of El
Niño-Southern Oscillation (ENSO) in previous studies. However, whether
the basin-wide warming/cooling of the Indian Ocean (IO) independent of
ENSO could affect the MJO remains elusive. Here, we show that the MJO
tends to initiate more westward and only propagate confined over the IO
under warm conditions during boreal summer. In contrast, a cold IO
results in an eastward-shifted MJO initiation and smooth propagation
across the Maritime Continent (MC)-western Pacific (WP). The genesis
location is mainly associated with warm ocean beneath the MJO, which
accumulate more during warm conditions. Additionally, the warming of the
IO induces anomalous anticyclone and stronger vertical wind shears over
the WP, which synergistically lead to stronger Rossby wave while weaker
Kelvin wave components, thereby inhibiting the MJO eastward propagation.
Moreover, the suppressed convection and thus low-level Kelvin easterly
wind anomalies over the MC-WP region become weaker with the warming of
the entire IO. Consequently, the premoistening dominated by the
high-frequency synoptic-scale meridional advection decreases and causes
nonpropagating MJO during boreal summer. These findings highlight that
interannual variations of the MJO could be attributed by considering
independent modulation effects of the IO.