Extreme Temperature Diary-November 2, 2018/ Topic: New Research On The Changing Jet Stream

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Friday November 2nd… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)😊.

New Research On The Changing Jet Stream

The biggest news coming out of the climate world this week was the publishing of another study about the jet stream coauthored by the most famous climate scientist, Dr. Michael Mann. Due to the Hockey Stick Graph, other research, public speaking, and many books, such as the Madhouse Effect, Dr. Mann is now the public face of the climate issue. Also, if I see significant, viable new research which unravels some of the mystery of what carbon pollution is doing to the environment, either on a global or regional basis, I’ll jump on that on this site as has been the case the last couple of years.

It appears that about a third of my posts deal with phenomena in association with the changing jet, using those Pivatol Weather 500 millibar anomaly charts. I’ve presented Dr. Mann’s past work on the changing jet, such as in this post: https://guyonclimate.com/2018/07/21/extreme-temperature-diary-july-21-2018-hot-topic-unusual-blocky-northern-hemisphere-pattern/

Dr. Mann has been busy refining his prior work on the jet, which has been reported in many articles this week such as this from Inside Climate News: https://insideclimatenews.org/news/31102018/jet-stream-climate-change-study-extreme-weather-arctic-amplification-temperature

Quoting and reposting this entire article:

Greenhouse gases are increasingly disrupting the jet stream, a powerful river of winds that steers weather systems in the Northern Hemisphere. That’s causing more frequent summer droughts, floods and wildfires, a new study says.

The findings suggest that summers like 2018, when the jet stream drove extreme weather on an unprecedented scale across the Northern Hemisphere, will be 50 percent more frequent by the end of the century if emissions of carbon dioxide and other climate pollutants from industry, agriculture and the burning of fossil fuels continue at a high rate.

In a worst-case scenario, there could be a near-tripling of such extreme jet stream events, but other factors, like aerosol emissions, are a wild card, according to the research, published today in the journal Science Advances.

The study identifies how the faster warming of the Arctic twists the jet stream into an extreme pattern that leads to persistent heat and drought extremes in some regions, with flooding in other areas.

The researchers said they were surprised by how big a role other pollutants play in the jet stream’s behavior, especially aerosols—microscopic solid or liquid particles from industry, agriculture, volcanoes and plants. Aerosols have a cooling effect that partially counteracts the jet stream changes caused by greenhouse gases, said co-author Dim Comou, a climate and extreme weather researcher at the Potsdam Institute for Climate Impacts Research and the Vrije Universiteit Amsterdam.

“The aerosols forcing was a bit of a surprise to us,” Comou said. “Those emissions are expected to decrease rapidly in the mid-latitude regions in the next 10 to 30 years” because of phasing out of pollution to protect people from breathing unhealthy air.

In recent decades, aerosol pollution has actually been slowing down the global warming process across the Northern Hemisphere’s mid-latitude industrial regions. If aerosol emissions drop rapidly, as projected, these regions would warm faster.

That would change the temperature contrast between the Arctic and mid-latitudes, which would dampen the warming effect of greenhouse gases on the jet stream. By how much depends on the rate, location and timing of the reductions, and the offset would end by mid-century, when man-made aerosols are expected to be mostly gone and no longer reflecting incoming solar radiation, said Pennsylvania State University climate scientist and study lead author Michael Mann.

Repeats of the Summer of 2018?

The jet stream is a powerful high-altitude wind that shapes and moves weather systems from west to east. Different branches of the jet stream undulate from the subtropics to the edge of the Arctic. In the past 15 years at least, the jet stream has been coiling up more, slithering farther north and south. When it gets stuck in the extreme pattern identified by the scientists, it leads to more deadly and costly weather extremes.

That extremely wavy pattern, called “quasi-resonant amplification,” was evident during the extreme summer of 2018, Mann said.

Extreme Weather and the Jet Stream

It played out in real time on TV and in newspaper headlines about droughts, floods, heat extremes and wildfires—an “unprecedented hemisphere-wide pattern,” Mann said. “It played a key role in the large-scale jet pattern we saw in late July, associated with deep stagnant high pressure centers over California and Europe.”

That brought blazing temperatures and wildfire conditions to California, flooding over the Eastern U.S. and unprecedented heat to the Scandinavian Arctic region, as well as a six-month heat wave and drought across parts of Central Europe, all events showing a clear global warming fingerprint, according to scientists.

The new study focuses on summer extremes, while other research has looked at how global warming affects the jet stream in winter.

What Happens in the Arctic Doesn’t Stay There

Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research who was not involved with the new research, said the study has some “compelling new evidence on the link between amplified Arctic warming and extreme mid-latitude weather during the summer months.”

What happens in the Arctic doesn’t stay there. Increased melting of reflective sea ice in summer exposes more dark-colored ocean to absorb heat, and that heats the surrounding land. As Arctic warming races ahead of the rest of the global average, the temperature contrasts that drive the jet stream are reduced, and the river of wind more frequently twists into sharp and slow-moving or stationary waves.

“When the jet stream enters this wavy state, extreme weather tends to occur on either side of the amplified ridges and troughs as the storm track becomes locked in place,” Swain said. Then, specific regions experience long periods of cool and stormy or, contrarily, hot and dry weather, he added.

For today’s discussion let’s more thoroughly examine the Inside Climate News’s  graphic: 

Extreme Weather and the Jet Stream

On the right side of the graphic we see deeper reds and blues representing deeper troughs and stronger, warmer ridges in association with jet stream amplification now linked to global warming. As early as the 1980s I learned that when looking at a global 500 millibar chart for “long range or extended forecasts” for the 4-10 day out period weather forecasting purposes, it was very important to note how many trough/ridge configurated patterns were occurring around the Northern Hemisphere. The more amplified the patterns the stormier the weather at the base of each through. A “four wave” pattern having four ridge/trough configurations was stable, so for quite a long time during a season like summer the weather you saw was the weather you got. If it was dry and hot that weather pattern would persist directly beneath a ridge, which would not move.

Apparently during the summer lately we are seeing more intense four wave, stable patterns around the Northern Hemisphere. By contrast in 2018 the East Coast of the U.S. got stuck just to the east of a long wave trough, which did not shift for most of the summer,  producing record wet conditions. The West, like in 2017, was stuck under the corresponding dry long wave ridge. One “wanted” pattern, the less amplified “five wave” or more configuration around the Northern Hemisphere, is progressive in nature; thus, over a given area not too severe storminess would be replaced by a relatively short dry period followed more beneficial precioitation…a pattern not conducive for heat waves or droughts, a farmer’s delight. If you really want to get into the weeds of the physics and mathematics behind the study involving atmospheric wave dynamics please read the study:

http://advances.sciencemag.org/content/4/10/eaat3272 

Dr. Mann writes more about the new jet stream study here: 

In the future I’ll continue to use some hemispheric 500 millibar charts to count the number of wave/trough configurations letting all know how the study is verifying via some examples. The summer of 2019 will be interesting to study, but before then we will probably see other climate change related weather phenomena, which I’ll be reporting.

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Here is some weather and climate news  from Friday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity.)

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The Climate Guy

 

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