US CLIVAR ENSO Diversity Workshop

Workshop Summary

It is well known that no two ENSO events look alike. Over the last decade, the longitudinal location of warming during El Niño events has received a large attention due to its influence upon atmospheric teleconnections and remote impacts. Several different approaches, indices, and definitions have been introduced to categorize the various El Niño flavors. While the literature on this topic is extensive, there are still many open questions about the existence of a continuum versus preferred longitudes of maximum warming, dynamical processes, impacts, possible precursors, and the ability to predict the different flavors. It is also unclear whether observational and ocean analysis datasets are consistent in reproducing the various aspects of ENSO diversity, and of adequate duration to provide a statistically significant characterization of the different flavors. Proxy data are a promising approach, and the information they provide needs to be explored and compared with other observations and models.  The workshop hosted by the US CLIVAR ENSO Diversity Working Group, is intended to provide a venue for discussion and synthesis of all the above aspects of ENSO diversity, and identify key directions for future research.

The workshop will primarily include poster presentations. Few invited presentations will provide a review of our present state of knowledge, and facilitate the discussion.

Discussion will be guided by nine overarching questions:

1. [Types vs. continuum]  Do discrete classes of ENSO events emerge from obs/paleo records and models?  Or is ENSO diversity better described as a continuum, with a few interesting extremes?
2. [Obs uncertainty] What are the main obs/proxy/reanalysis uncertainties that cloud understanding of past ENSO diversity, and limit the skill of ENSO forecasts?
3. [Impacts]  What are the most important global impacts of ENSO diversity, e.g. on teleconnections, extreme events, biogeochemistry, ecosystems, and society?
4. [Past changes] What historical/paleo variations in the ENSO PDF are clearly statistically & dynamically attributable to radiative forcing changes, against the backdrop of random intrinsic modulation of ENSO?
5. [Future changes]  How long until the impacts of future climate changes on ENSO diversity and predictability are detectable in observations?  Are they detectable already?
6. [Model performance]  What do CMIP3/CMIP5 models capture best about observed ENSO diversity?  What do most models fail to capture, and why?
7. [Theories and simple models]  Are existing ENSO theories and reduced-complexity models (either statistical or dynamical) able to capture the full ENSO diversity found in obs and GCMs?  How can the theories and simple models be improved, unified, extended, and used to improve GCMs and ENSO forecasts?
8. [Predictability]  Do certain ENSO types/extremes offer significantly enhanced/degraded predictability?
9. [Forecast skill]  Are existing forecast systems significantly better at predicting some ENSO types/extremes than others?