Tuesday, 28 July 2015

2015's el-Nino

Possible Strongest El Nino on Record Gets Another Kick From Upper Ocean Heat

27 July, 2015

For the month of July, El Nino crossed solidly into strong event thresholds. Temperatures in the key indicator Nino 3.4 region have continued to rise overall, hitting 1.5 degrees Celsius above average during the first week of the month, then hitting +1.7 and +1.6 C during the second and third weeks. Model consensus continues to show the heat building — hitting around +2.1 C in the average by October, November and December.

(A NOAA comparison shows the 1997-1998 El Nino at peak heat during November of 1997 [left frame]. The right frame image shows the 2014-2016 El Nino during its mid July ramp-up. Note the hot blob of water off the US West Coast in the July 2015 image. Heat in this region tends to drive an atmospheric feedback that continues to push more warm water into the Eastern and Central Equatorial Pacific. Note that, due to this and other factors, the 2014-2016 will likely also hit a peak intensity during October or November. An intensity that could exceed the monster 1997-1998 El Nino event. Image source: NOAA Environmental Visualization Laboratory.)

So much warming in this region of the Pacific would be enough to make the 2014-2016 El Nino nearly as strong as the 1997-1998 event. But, ominously, a few of our more trusted models show temperatures peaking out at around +3 C for the Nino 3.4 zone. A level that would exceed all previous thresholds for El Nino strength. It’s the kind of heat pulse that would re-write the record books for strong El Ninos. The kind that would enable global surface air temperatures — under the constant and building pressure of an excessive human greenhouse gas emission — to hit new and troubling record highs over the coming months.
For such a record event to happen, there needs to be a powerful plug of heat just beneath the ocean surface. It needs to back up into the Central Pacific and it needs to be intense enough to deliver the kind of heat energy predicted. And all indications are that the available heat energy for this potentially record event on the way.
A Massive Plug of Upper Ocean Heat

Back in March one of the strongest westerly wind outbreaks ever to occur in the Western Pacific sent a powerful wave of heat rippling out beneath the broadest section of equatorial ocean water in the world. Hot water, driven to near record temperatures by a human-forced warming of the atmosphere and ocean system spread out just below the surface and began to up-well — contacting the airs just off the West Coast of South America.
(Upper ocean heat is again ramping above the 1.8 C positive anomaly mark for the Equatorial Pacific. A sign that more surface warming is likely on the way. Image source:NOAA CPC.)

At that time, the NOAA measure of heat accumulated in the upper 400 meters of the Equatorial Pacific, showed temperatures had rocketed to 1.8 degrees Celsius above average for the entire basin. Since then, a series of west wind outbreaks have continued to pile abnormally warm water into the upper ocean environment — keeping temperatures in the range of 1.1 to 1.8 C above average.

Now, due to a very long duration westerly wind outbreak that began during late June and has extended for more than a month, upper ocean heat content is again on the rise. As of last week, it had rocketed again to 1.8 degrees Celsius above average for the basin. And signs indicated there was at least a moderate potential for continued strengthening of this heat pulse. Observational data and GFS model runs show a continuing westerly wind flow over the Western Pacific. Winds circling around two lows parallel to one another and straddling the Equator near 170 East are predicted to increase to near 25 to 35 mph over the next few days. It’s the most recent surge in this very long duration westerly wind outbreak. One that will likely only continue to drive more heat into the upper ocean environment.
Kelvin Wave
(A strong Kelvin Wave is now backing more and more heat into the Nino 3.4 zone. In watching the progress of upper ocean heat in this visualization, we could be witnessing the final stages of an event that will go down in the record books. Image source: NOAA CPC)

Already, we can see the strong, warm Kelvin Wave — which has been a persistent feature since mid March — becoming reinvigorated. The Kelvin Wave is now rebounding away from coastal South America even as its warm water zones expand. Its hottest waters are heading more toward mid Ocean. A trend that, if forecast models prove correct, will deliver serious heat to the middle Pacific sea surface region this Fall.
It’s a massive delivery of heat that we can now watch in slow motion. One that could now be in the process of delivering one of the strongest, if not the strongest El Nino in the history of record keeping for this ocean warming event.

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