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El Nino and Rain in South America December 31, 2015

Posted by wmmbb in CLIMATE CHANGE.

It was a puzzle to me as how El Nino would be attributed as the cause for the heavy rain and flooding in Northern Argentina, Southern Brazil, Paraguay and Uruguay. So I posed the question at Skeptical Science with responses: How did El Nino bring on these heavy rains?.

According Maps of the World:

A unique feature of South America Climate is the El Nino. Every two to seven years the cold dry Peru Current weakens and warm waters from the south rush along the coast in a southward direction. The El Nion affects the Climate of South America and causes heavyrainfall in the dry parts of South America.

Acknowledging that South America lies between the Pacific and Atlantic Oceans, given the barrier presented by the Andes, it both surprises and is contrary to my expectations that El Nino would exert such as effect as to cause torrential rain in South East portion of the continent. I would expect that the Atlantic would be exerting the major influence. The interaction and interrelationship between ocean and atmosphere and the transport of moisture in the upper atmosphere leaves me non nonplussed, and general explanations are not readily given, such as the potential of jet streams to divide and direct air flows with consequential weather and climate effects.

The Bureau of Meteorology reports:

El Niño remains near its peak, with the tropical Pacific Ocean and overlying atmosphere consistent with a strong event. Models suggest the event will start to decline in 2016, but a return to ENSO-neutral is not likely until at least autumn.

Sea surface temperatures and cloud patterns near the Date Line remain well in excess of El Niño thresholds. The Southern Oscillation Index (SOI) has returned to El Niño levels following a brief period of neutral values. Below-surface ocean temperatures in the eastern tropical Pacific remain significantly warmer than average, but clearly some cooling has occurred in the past fortnight. Changes in the sub-surface are an important indicator, as the sub-surface plays a significant role in maintaining the strength and longevity of El Niño events.

Generally, meteorological reports do not give me a sense of the processes involved, although this a good description of the measurements. The energy dynamics should be  relatively straightforward. What is the role of deep currents and the jet stream in distributing effects of the El Nino to other continents, or increasing global mean surface temperature?

Skeptical Science provided the following responses to my question. Rob Painting provides a summary which taken with the  role of  the Southern Jet Stream starts to give an overall story:

Key Points:

  • El Niño puts in an appearance every two to seven years, and involves the abrupt discharge of heat from the tropical ocean to the atmosphere – often resulting in years with warmer-than-average global surface temperatures.
  • Every now and then a very large event occurs, such as the one in 1997-1998 which broke surface temperature records at the time and caused worldwide disruption and damage.
  • The current large build-up and eastward movement of heat in the equatorial subsurface ocean strongly hints at a powerful El Niño developing this year.
  • A powerful El Niño is by no means guaranteed, but should one develop mid-2014 to mid-2015 would likely be the hottest 12 months ever recorded. Unfortunately widespread weather-related chaos and mass coral bleaching is almost certain to follow.

The first point seems the most informative to me. This gives me the impression that it is a chaotic event and is perhaps a indicator of increasing disequilibrium in the Earth’s Climate System. But then, why has it taken so long since the last major event in 1998? There was another event in 2010 that did not have major effects. Rob of Newcastle as Cattallaxy is predicting that this EL Nino will be similarly overwhelmed by a large cold northward current. I am attempting to comprehend general patterns more than local events. The physics of heat flow sound right to me. I suppose time is everything – and that may go some way to explaining variability.

Sceptical Science made reference to an article by Eric Holthaus in Slate:

The week of Christmas was the warmest on record by far for a vast stretch of the eastern United States from Texas to Maine. In Philadelphia, every single day this month has been warmer than normal—if that word even retains meaning during a month like this.

While this month’s extreme weather is primarily due to an atmosphere supercharged by the record-breaking El Niño, it’s also an example of the kind of unnerving meteorological event that’s becoming more likely as climate change plays an increasingly large role in daily weather. The New York Times called it “a fitting end to the warmest year on record.” Together, El Niño and climate change have combined for a year unlike any other in human history—a harbinger of an altered planet.

– Eric Holthaus, Slate, Dec 29, 2015

None of this provides a straightforward answer. So then there is The Guardian article linked to by Skeptical Science:

From some of the worst floods ever known in Britain, to record-breaking temperatures over the Christmas holiday in the US and and forest fires in Australia, the link between the tumultuous weather events experienced around the world in the last few weeks is likely to be down to the natural phenomenon known as El Niño making the effects of man-made climate change worse, say atmospheric scientists.

“We expect 2016 to be the warmest year ever, primarily because of climate change but around 25% because of El Niño,” said Scaife, who added that the phenomenon was not linked directly to climate change but made its effects worse.

Surely, climate change is diverse atmospheric and oceanic phenomena directly influenced by the increase in the energy balance.

Here is just one of many explanation of ENSO:



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