Sunday, October 18, 2009

Routine El Nino causes Unexceptionally High Temps

We are really just entering an El Nino -- in fact, the latest SOI is actually in the opposite direction -- but already we are seeing strong September temperatures and, now, a very strong hurricane in the eastern Pacific, Hurricane Rick, a Cat 5.

In a recent press release, John Christy of the Univ of Alabama at Huntsville says:

A relatively routine El Nino Pacific Ocean warming event shouldn't cause the hottest tropical September in the past 31 years, but it did, according to Dr. John Christy, professor of atmospheric science and director of the Earth System Science Center at The University of Alabama in Huntsville. On top of a record-setting month in the tropics, September 2009 was also the second warmest September on record both globally and in the Northern Hemisphere.

"Who would have predicted those temperatures in the atmosphere when the sea surface temperature has been bumping along so nonchalantly?" Christy asked.

Normally, warming in the atmosphere during an El Nino is somewhat linked to rising sea surface temperatures in the Equatorial Pacific. Atmospheric temperatures in September, however, were significantly warmer than might have been predicted based on sea surface temps.

Sea surface temps for September in a key region of the Pacific were on the order of 0.83 C warmer than average, and the tropical atmosphere was 0.51 C warmer than seasonal norms," Christy said. "We've seen water temps about this warm twice in the past decade (2004-2005 and 2006-2007) without seeing this surge in the atmosphere.

"If you go back to the big El Nino of 1997-1998, sea surface temps (SSTs) in September 1997 in that same part of the Pacific were about 2.29 C warmer than normal, but the tropical atmosphere was only 0.4 C above average.

"Other things drive atmospheric temperatures in addition to SSTs, so it seems this would have been a warm September even without the El Nino."
Rick seems to be weakening a little, but it will probably still have the strongest ACE of any eastern Pacific hurricane this year.

Globally, though, ACE values are at a 30-yr low, a bit of a puzzle.

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