|
The term "El Niño" (or similarly "ENSO") describes the episodic
warming and cooling of the eastern tropical Pacific on a timescale of
several years. The figure above displays several decades of average
eastern tropical Pacific sea surface temperatures. A tendency to
vary irregularly on a timescale of roughly 3-7 years (i.e., interannually)
is evident.
A motivation to study the dynamics of El Niño is the
possibility of improvement in prediction ability (the major events in
1982 and 1998 each had roughly 2,000 deaths attributed to
them).
Furthermore, in light of increased concern about climatic response to
human-induced global change, improved understanding of El Niño
dynamics may allow us to better assess potential feedbacks between
tropical Pacific variability (which has global impacts) and global
warming.
Rapidly varying weather, and especially westerly wind bursts (tropical
Pacific weather events with a timescale of weeks), have been
frequently suggested to drive ENSO. We are investigating the
possibility that westerly wind bursts are in fact modulated by ENSO
itself. In our first study of this hypothesized two-way feedback, we
combined analysis of satellite scatterometer data with experiments
carried out using an ENSO computer forecast model of intermediate
complexity, and we found that the inclusion of observationally-based
westerly wind burst modulation by ENSO has a huge effect on simulated
interannual variability. We extended this work using a more
sophisticated ENSO model which combines an ocean general circulation
model with a statistical atmospheric model (i.e., a hybrid coupled
model). We added an explicit westerly wind burst component to the
model atmosphere with guidance from a twenty-three year observational
record, and we parameterized westerly wind burst occurrence such that
the likelihood of an event depends on the western Pacific warm pool
extent. The modulation of westerly wind bursts strongly affected
simulated ENSO characteristics in this model.
|