El Niño 2015 could be the strongest ever

Tuesday, December 8, 2015

The Pacific Ocean warming phenomenon and its cooling counterpart, La Niña, have a major impact on our weather and the experts are warning that this year's El Niño could be the most powerful on record

by PHIL CHADWICK

The earth's atmosphere system is indeed finite. Everything is connected. The cause and effect chain might be long, but it exists and there is no denying it. The length of the C-E chain might make it challenging to understand and prone to being broken by skeptics. How can the sea temperature in the Pacific Ocean impact Ontario, Canada and the world? Bob Dylan said it – the answer is "blowing in the wind."

The sea surface temperatures over the vast Pacific Ocean are second only to the seasons for controlling the global weather. The unusual warming of the equatorial Pacific has been recorded since 1700 and occurs regularly every two to seven years. The annual weak warm ocean current that flows southwards along the coast of Peru and Ecuador about Christmas-time was first called El Niño, which is Spanish for 'the boy Christ-child.' Fishing was terrible in the warm currents. The El Niño term was expanded to include the general warming of large tracts of the Pacific Ocean. An El Niño episode generally lasts a year or two. The flip side of an El Niño is the relative cooling of the equatorial Pacific known as La Niña.

Together, the El Niño and La Niña ocean currents influence the atmospheric circulations, which are called the "Southern Oscillation." The combination of the atmospheric and oceanic circulations is termed the "El Niño-Southern Oscillation" or ENSO for short.

Before satellites, there was no way to quickly and accurately measure the extent of any temperature deviation within the oceans. The Southern Oscillation Index (SOI) was first proposed by H.H.

Hilderbrandson in 1897 to use pressure differentials as a proxy to reveal oceanic temperature differences. The SOI is simply the difference in air pressure between two locations in the Pacific – the island of Tahiti and Darwin, Australia. Sustained negative values of the SOI below -8 often indicate El Niño episodes. Values of the SOI date back to 1876 and I have actually used these quantities to correlate with the type of convection that occurs over Ontario, but that's another story. The current SOI time series reveals that this latest El Niño actually started in the summer of 2014.

Fast forward to today. With satellites, meteorologists are now able to do a better job of analyzing and diagnosing the state of the Pacific Ocean in real time. What has happened is that on Aug. 13, 2015, experts from the U.S. National Oceanic and Atmospheric Administration claimed that El Niño 2015 could rival the top events on record. There has been a media storm ever since.

The latest satellite measurement of sea surface temperature from Aug. 5 shows temperatures of 1.0 Celsius above normal and on a climbing trajectory over a large area of the central Pacific. The comparison of the current temperature anomaly with that from 1997 on the left (below) is remarkable. The equatorial Pacific is warmer over a larger area and centred on the International Dateline away from the South American coast. The 1997-98 El Niño was the strongest on record since 1950.

Ontario farmers will remember the ice storm of 1998. The weather conditions in January of that year were certainly correlated with the atmospheric flows that resulted from the so called "Super El Niño." I do not wish to make direct correlations, but we can learn from history and learning is always a good thing.

An examination of climate data using only El Niño events characterized by mid-Pacific warming reveals the following average impacts on surface temperatures. The West Coast and Rockies are warmer than average. The mid continent was colder than normal. The extreme East Coast was a bit warmer than average.

Ontario farmers will also remember and recognize this pattern from last winter and even this summer. It is not surprising, since this El Niño pattern got going last summer. Persistence is a good place to start any forecast. What is happening now will continue – until it changes.

My very first Better Farming article in October 2013 was no accident. "Climate change: the new normal isn't what it used to be" focused on the significant weakening of the jet stream that results from the differential faster warming over the Canadian polar regions as compared to the equator. The analogy comparing a strong river to a meandering stream was made in order to deliver the message. That analogy still applies and I have used it in describing the Polar Vortex and in subsequent articles.

With an El Niño, and especially one associated with mid Pacific warming, a strong ridge of high pressure is built along the west coast of North America. The warm air creating the ridge is heated by the abnormally temperate waters of the Pacific. The jet stream is typically deflected northward anyway because of the Rockies, but this effect is amplified by the strong ridge of high pressure.

In the "old days," the strong jet stream shooting northward would carry that momentum and not turn southward again until mid continent or even further east. This would mean that Ontario would typically experience the warmth of the El Niño. Winter warmth means more rain than snow and probably less precipitation in total, as is typical with being on the edge of any ridge of high pressure.

With climate change and a weaker jet stream, there is not as much momentum in that flow anymore. Instead, a meandering stream is more than likely to flow southward in the lee of the Rockies after climbing over the barrier. What goes up comes down. Meandering flows tend to have large amplitude bends and even oxbow lakes. The Polar Vortex is the atmospheric equivalent of the hydraulic oxbow.

Weather systems move more slowly since they are now guided by a weaker flow. Atmospheric circulations are more apt to split and create patterns conducive to freezing rain.

Meteorologists have seen this before. Old timers look at flows, circulations, patterns and shapes and have a pretty fair idea of just what might happen. It is not, after all, rocket science. That being said, there will certainly be much diversity of opinion upon what the future will bring and no one can claim to be absolutely right.

Time will tell, but history will repeat itself. Ontario farmers would be well advised to remember last winter. The intensification of the El Niño pattern could make it colder and thus snowier. As far as freezing rain patterns go, the meteorological conditions are so critical that even a small change flips the freezing rain to ice pellets or even snow with correspondingly much less impact.

Weather is important. The alarming observation is that both weather and climate have changed within our lifetimes. Experts who look at this material everyday are now concerned that El Niño 2015 could be the strongest ever on record – and those particular records date back to 1950. "This definitely has the potential of being the Godzilla El Niño," added Bill Patzert, a climatologist with NASA's Jet Propulsion Laboratory in La Cañada Flintridge, Calif. As a meteorologist, however, I try to refrain from such media hype and stick with "just the facts, ma'am."

I might add a special concern for California and the West Coast that has been ravaged by drought and fires and the subsequent loss of vegetation to anchor the soils. El Niño patterns tend to deliver rain events as per the accompanying map. Rain and soil with no thriving root system equates to mud slides. The much needed water might not hang around long enough to fill the depleted aquifers. If the weather is important, the collection of elements that make up our environment are even more so. BF

Phil the Forecaster Chadwick has been a professional meteorologist since 1977, specializing in training, severe weather and remote satellite and radar sensing.