Mixed signals in pacific about el nino forming or not

[cycloneye]

CURRENT STATUS as at 18th August 2004:
Next update expected by 25th August 2004 (one week after this update).

The risk that we're seeing the beginnings of an El Niño event has increased during the past two weeks. Ocean surface temperatures remain significantly higher than average in the central Pacific Ocean, the SOI is persisting in negative values for the third successive month, and cloudiness has increased around the equatorial dateline. These are all classic signatures of a developing El Niño.

However, the Trade Winds have returned to close to or a little stronger than average east of the dateline, after being strongly weaker than average during much of July. Subsurface temperatures seem to have responded to the increased winds with a decline in the strength of subsurface warming during the first two and a half weeks of August.

The evolution of a westerly wind burst (WWB), presently over the western Pacific, could be crucial. If it fails to penetrate east of the dateline, conditions will remain delicately poised. However, a continued eastward propagation of the WWB, which would result in a renewed weakening of the central Pacific Trade Winds, may be sufficient to trigger an El Niño event.

Computer model guidance indicates continued warmer than average conditions across the central Pacific. Even in the absence of a clearly defined El Niño event, this would be sufficient to increase the risk of areas of below average rainfall and above average temperatures persisting in parts of eastern Australia, especially when combined with negative SOI values.

At link below there is more information about this.

http://www.bom.gov.au/climate/enso/index.shtml

My opinion about this is that el nino may appear in a weak form but will not be a big influence to shut down the ladder part of the season,october and november but things can change so let's watch the ENSO factor in comming weeks.

[x-y-no]

Interesting how the meaning of terms changes over time. I sure thought the original definition of "el nino" involved the weakening of upwelling on the coast of Ecuador and Peru. But now that seems to have nothing to do with it any more, and all we care about is central Pacific SST without regard to the eastern Pacific at all.

[Aslkahuna]

Yes, that was the original definition of El Niño from 200 years ago. The reason now for a broader definition is the discovery of the connection
between that original Niño with the ENSO which is a larger scale phenomenom. Incidentally, the cold phase was originally called El Viejo (the Old Man) rather than La Niña which which is a term coined not so long ago.

Steve

[x-y-no]

Yes, that was the original definition of El Niño from 200 years ago.

Wow ... didn't seem that long ago to me. Back when I was first learning something about this stuff in 1972, the coastal upwelling issue still got mentioned.

The reason now for a broader definition is the discovery of the connection
between that original Niño with the ENSO which is a larger scale phenomenom. Incidentally, the cold phase was originally called El Viejo (the Old Man) rather than La Niña which which is a term coined not so long ago.

Steve

Yeah, I understand that. But I'm not so clear on the criteria that are used to decide if we have one - is it only SST in the central Pacific? Or are there other things? I ask because I don't see too dramatic a difference between 2002, which was called a weak el nino, and this year which (so far at least) isn't. Is this because of other measures, or am I wrong about the temperature anomaly being similar?

[PurdueWx80]

The southern oscillation index (SOI) is another long term indicator of ENSO. It's basically the different in pressure between Tahiti (western Pac) and Darwin (Galapagos Islands). If it is negative for a long time, as it has been for 3 months, on average, it indicates that the pressure gradient (over the whole Pacific) sends the winds from the west to east, pushing warm water towards South America. Normally it's the other way around (E to W), which is why there is upwelling of cold water along the Peruvian coast. It is all much more complicated than this, but I think that is the easiest way to understand what is happening. Of course, the water profiles are controlled by and help control atmospheric motions, so when these things change back and forth between neutral, El Nino, and La Nina, there are changes in global weather patterns as a result. Our Earth is an amazing place full of all kinds of connections. Not sure if anyone has mentioned it, but JB (Joe Bastardi...Accuweather meteorologist for the newbies) calls the current state of affairs El Loco because it is in between the three main signals. Wonder if it'll catch on?