Alladi Ramakrishnan Hall

ENSO Diversity, Asymmetry and Extremes: A Unifying High-Frequency Driver

Raghu Murtugudde

University of Maryland

El Nino-Southern Oscillation or ENSO has been the poster-child for a
highly predictable seasonal-to-interannual climate variability signal. And
yet, the failed 2012 and 2014 ENSO predictions have raised questions about
the intrinsic predictability of ENSO, especially when considered in
conjunction with the variations in surface warming patterns associated
with ENSO. Another fundamental question that has remained unanswered is
whether ENSO is a self-sustained oscillation or a damped oscillator that
needs an external trigger and why some ENSO warm events grow to be much
stronger than others. The asymmetry in the warm and cold ENSO cycles
remains to be fully understood also. A unifying mechanism is proposed here
by focusing on the state-dependent high-frequency forcing, namely, the
Westerly Wind Bursts (WWBs). ENSO diversity is of particular interest for
monsoon-ENSO interactions since the question of who leads when El Nino
dances with the Indian summer monsoon remains to be fully understood. The
droughts of 2012 and 2014 are of interest in this context. The impact of
ENSO on the summer and winter monsoons, especially in the context of
Indian Ocean warming must now be considered along with ENSO diversity and
ENSO response to global warming. The discussion will address some of these
aspects to speculate on what remain fundamental to the ENSO mode.