MJO Teleconnections to the Southern Hemisphere During El Niño, La Niña, and Neutral Years

The Madden Julian Oscillation (MJO) and the El Niño Southern Oscillation (ENSO) are
important modes of tropical variability that can significantly impact both tropical and
extratropical weather and climate and are thus a potential source for improving subseasonal
to seasonal prediction of our weather and climate. MJO teleconnections and their associated
changes during different ENSO background states have been extensively researched in the
Northern Hemisphere (NH). However, similar understanding is absent in the Southern
Hemisphere (SH) and thus warrants in-depth study. ENSO modifies the background
circulation, and this altered background state causes changes in the MJO teleconnection
patterns. In our study using the reanalysis datasets, we observe the ENSO-induced changes in
MJO teleconnections for three different seasons. We identified that the changes, relative to
neutral ENSO years, are strongest during El Niño years in the early MJO phases (8, 1, 2, and
3), and during La Niña years in the late MJO phases (4, 5, 6, and 7). The sensitivity of the
modulation is highest during the austral summer and is lowest during the austral winter. The
strength and duration of the convection plays an inevitable role in understanding the
relationship between ENSO and MJO. The non-linearity of the ENSO-MJO interactions
showed that during the austral summer La Nina has a higher influence over the MJO and
hence the resulting teleconnection patterns are more SAM-like. This also implies that there is
a possible stratospheric mechanism for these patterns. However, during the El Nino years we
identified more Rossby wave-like patterns indicating the importance of tropospheric
pathways. Thus, this study provides new insights into ENSO-MJO teleconnections in the SH
and the dynamics causing them.