Thursday, October 27, 2011

ENSO and tornadoes?

Today, I had a nice discussion with a colleague who showed me some fascinating preliminary results of some analysis he'd done regarding the El Niño/Southern Oscillation (ENSO) and tornadoes.  I don't want to steal his thunder, but what he showed me was that ENSO could explain about 10% of the variability in tornado occurrences.  This number struck me as being a reasonable one - my position is not that ENSO is irrelevant to tornado occurrences, but rather that it's only a part of a much more complex set of processes that ultimately control tornado events.  Much of that complexity is beyond the pale of existing atmospheric scientific understanding, unfortunately.  The notion that only a relatively small portion of the variability can be attributed to ENSO seems both plausible and consistent with what understanding atmospheric science can offer at present.

Imagine my dismay when, later in the day, I read in the prestigious science magazine Nature for 22 September (p. 373) that "El Niño, a quasiperiodic cycling of tropical Pacific water temperatures, causes extreme weather around the globe."  This tidbit of journalistic excess really set my teeth on edge after my earlier discussion today!  ENSO is just one of many quasiperiodic "cycles" (e.g., the North Atlantic Oscillation, the Pacific Decadal Oscillation, etc.) that affect the global weather patterns and no doubt more will be discovered with time.  ENSO is a player but far from the dominant one, and the resulting global weather pattern is the result of the interplay between all these processes (and those as yet undiscovered!).  Attributing events exclusively to El Niño is outright nonsense!

Although ENSO apparently does modulate global weather patterns, there are many causal linkages between that global pattern and tornadoes, many of which remain unknown to science, at least in detail.  To say that El Niño causes extreme weather is a ludicrous exaggeration of its influence.  This sort of easy "explanation" often appears in media coverage of extreme weather events as a sort of non-explanatory explanation, similar to the "clash of air masses" nonsense often heard in media coverage after tornado outbreaks.

Once again, I'm reminded of the vast gulf between what's offered to the public and what I know as a severe weather scientist.  I expected better of Nature, clearly, and was disappointed to see such an ignorant "explanation" for extreme weather events within this magazine.  I've seen many scientists tempted by the siren song of ENSO as a way to explain interannual variability of tornadoes.  It appears to be a seductive hypothesis, perhaps because there is just enough of an actual influence to convince many to pursue the topic - I wound up publishing a paper addressing some of the myriad problems in trying to establish a causal connection between El Niño and tornadoes.  But the beat goes on, nevertheless - like the "clash of air masses," it's a simple "explanation" that just won't go away.


Stephen said...

Thank you for writing about this almost untouchable subject...untouchable in that the song goes on and on, not with doubts but with better understanding being up-welled as technological advances combined with a longer lasting (historical background/climate)get us beyond the tip of the iceberg. The simplicity of the compounding El Nino phenomenon leaves those not impelled to investigate in the "I didn't know that I didn't know" state, frustrating those who have bothered to do some digging. Bravo!

Chuck Doswell said...

For the record ... this is Stephen Sponsler.