Thursday, 27 February 2014

The meandering Jet Stream

Dr Jennifer Francis and the Year-Long Blocking Pattern

25 February, 2014

Last year, on March 30th, I wrote this:
Over the past decade, an increased prominence of blocking patterns has emerged. These events happen when the polar jet stream gets stuck in large meanders. These meanders result in a long persistence of weather for regions affected by these blocking patterns. New papers by Jennifer Francis and other polar researchers last year linked the increasing occurrence of these new blocking patterns to an erosion of Arctic sea ice…
Low pressure systems keep forming over the Bering and Okhotsk seas. Warmer air temps keep invading the American and Canadian west. The eastern part of the North American continent sees a continuous colder air invasion from the Arctic. The Arctic remains much warmer than average…

I may have well written the same thing today. For the weather pattern is mostly unaltered.

Blocking Pattern February 24
(High amplitude blocking pattern plainly visible over the US and Canadian West along with associated trough over the Central and Eastern US in the February 24 Jet Stream model. Image source: University of Washington.)

In fact, if anything, this winter only saw its intensification with numerous polar vortex disruption events, a vicious Arctic heat anomaly that featured and Alaskan thaw in January and Sea Ice setting new record lows for the month of February, and an extraordinary western drought leading to a collapse in California farming and a 10-15 percent hike in prices at US grocery stores.

For a blocking pattern to have persisted for such a long time is somewhat unprecedented. According to the standard definition of blocks (what I’m referring to as blocking patterns) the systems generally tend to last for days or weeks. The most powerful of blocks, like the Bermuda High, tend to last, at most, for a season. But this West Coast and Pacific block has now remained in place for nearly a year. A more solid validation of Dr. Jennifer Francis’ hypothesis — that sea ice melt can result in large Jet Stream meanders and ‘stuck’ weather patterns — is difficult to find.

Dr. Francis, writing for Yale 360 in 2012 queried:
Does it seem as though your weather has become increasingly “stuck” lately? Day after day of cold, rain, heat, or blue skies may not be a figment of your imagination. While various oceanic and atmospheric patterns such as El Niño, La Niña, and the North Atlantic Oscillation have been blamed for the spate of unusual weather recently, there’s now a new culprit in the wind: Arctic amplification. Directly related to sea-ice loss and earlier snowmelt in the Far North, it is affecting the jet stream around the Northern Hemisphere, with potentially far-reaching effects on the weather.
If we were to look for further validation, we might point to a period of storminess of epic intensity that re-shaped England’s coastline, tossed multi-ton boulders about as if they were toys, wrecked rail lines, and dumped so much rain over the English countryside that aquifers began erupting from out of the ground. Since mid December England has suffered its most intense and extended period of stormy weather ever on record. An ongoing disaster that has caused the government to re-consider all its previous assumptions about storm preparedness and should be causing it to reconsider its fossil fuel use as well.

UK House surrounded by floods
(UK home surrounded by floods. Image source: WTOP.)

For if anyone would say their weather seemed stuck, it would probably be the, still soggy, British. And perhaps those brave souls will provide some validation for Francis’ hypothesis and the predictive power it contains for any who dare to wield it.

Earlier this winter, noting that the shape of the Jet Stream hadn’t changed much since early 2013 and that the Pacific block still remained in place, I penned an article entitled: Winter 2013-2014 — Sea Ice Loss Locks Jet Stream into Severe Winter Storm Pattern for Much of US. The article still receives a remarkable flow of traffic, probably due to the fact that is was predictive of a set of conditions that are ongoing now, 70 days after it was written. And to whom do I owe the ability to generate such an insight? Why the author of the theory herself — Dr. Jennifer Francis.

Simply put, she predicted the weather would probably be extreme and that it would probably end up stuck. And so it has for at least three years running now. Don’t believe me? Just look at the US over the past three years. 2012 featured a drought that drove Mississippi river traffic into mud banks and wrecked a huge swath of the US corn crop before giving way to major flooding and heavy precipitation events that lasted long into 2013. The drought retreated westward where, by 2014, a ravaged California cut off all water to farmers. Meanwhile, the Eastern and Central US suffers a string of weather extremes that include swings in temperature of greater than fifty degrees over the course of just a few days, major winter storm events, flash melts, followed by flash freezes and tornadoes over snow.

Dr. Kenneth E. Kunkel, research professor for NOAA’s National Climate Data Center observed that the occurrence of extreme weather events for the US Midwest had increased by 40 percent over the past 20 years stating:
The number of extreme precipitation events in the Midwest has been increasing over the last 20 years, which is consistent with what we would expect from climate change, which has caused increased amounts of water vapor in the atmosphere. While the heavy snow of this winter is primarily a consequence of the persistent storm track, it may have been enhanced by the increasing amounts of water vapor in the atmosphere.

And this leads us nicely back to how climate change is currently wrecking the world’s weather — by weakening the Jet Stream and by amplifying the hydrological cycle. Both instances we have seen in glaring relief over the past few years of very extreme weather. Dr. Francis, in her own research found that Jet Stream winds over the US had weakened by as much as 20% during the period of 1948 to 2010. A significant reduction in its own right:

(Slowing of 500 mb winds from 1948 to 2010. Image source: Weather Underground.)

I bring up these instances and proofs to show, at least in the context of currently ongoing weather, that Dr. Francis’ claims have born out. Some scientists disagree, however, and appear to be using their clout to shut down what is now a useful tool for extreme weather prediction. And this is a sad event, because the climate state in which Dr. Francis’ predictions hold true probably won’t last for more than a few decades. The weather will certainly remain extreme. But by the time polar amplification has pushed the ice sheets to swiftly melt and human warming has pushed the tropics into a phase of rapid heating, the Jet Stream is likely to again intensify even as it re-centers around Greenland and the North Atlantic. Such changes will probably bring an entirely different set of weather concerns.

But, for now, as the northern polar region amplifies, Dr. Francis’ predictions bear out remarkably well. And this is as obvious as the daily weather report, awkward explanations of why the polar vortex collapsed so many times this year or why the Jet Stream is running so far north over Alaska aside…


Linking Weird Weather to Rapid Warming in the Arctic
Climate Change or Just the Weather: Experts Sound Off
Block (meteorology)
Dr. Jeff Masters: Our Extreme Weather Arctic Changes to Blame?
Arctic Warming, Extreme Weather Link Unclear

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