Our extreme weather: Arctic changes to blame?
"The question is not whether sea ice loss is affecting the large-scale atmospheric circulation...it's how can it not?" That was the take-home message from Dr. Jennifer Francis of Rutgers University, in her talk "Does Arctic Amplification Fuel Extreme Weather in Mid-Latitudes?", presented at last week's American Geophysical Union meeting in San Francisco. Dr. Francis presented new research in review for publication, which shows that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions.
Figure 1. Arctic sea ice in September 2007 reached its lowest extent on record, approximately 40% lower than when satellite records began in 1979. Sea ice loss in 2011 was virtually tied with the ice loss in 2007, despite weather conditions that were not as unusual in the Arctic. Image credit: University of Illinois Cryosphere Today.
Summertime Arctic sea ice loss: 40% since 1980
The Arctic has seen a stunning amount of sea ice loss in recent years, due to melting and unfavorable winds that have pushed large amounts of ice out of the region. Forty percent of the sea ice was missing in September 2007, compared to September of 1980. This is an area equivalent to about 44% of the contiguous U.S., or 71% of the non-Russian portion of Europe. Such a large area of open water is bound to cause significant impacts on weather patterns, due to the huge amount of heat and moisture that escapes from the exposed ocean into the atmosphere over a multi-month period following the summer melt.
Figure 2. The extent of Arctic sea ice loss in the summer July - August - September period in 2007 was about 1.4 million square miles (3.6 million square kilometers) greater than in 1980, according to the University of Illinois Cryosphere Today. For comparison, the lost ice coverage (orange colors) was equal to an area about 44% of the size of the contiguous U.S., or 71% of the non-Russian portion of Europe.
Arctic sea ice loss can slow down jet stream winds
Dr. Francis looked at surface and upper level data from 1948 - 2010, and discovered that the extra heat in the Arctic in fall and winter over the past decade had caused the Arctic atmosphere between the surface and 500 mb (about 18,000 feet or 5,600 meters) to expand. As a result, the difference in temperature between the Arctic (60 - 80°N) and the mid-latitudes (30 - 50°N) fell significantly. It is this difference in temperature that drives the powerful jet stream winds that control much of our weather. The speed of fall and winter west-to-east upper-level winds at 500 mb circling the North Pole decreased by 20% over the past decade, compared to the period 1948 - 2000, in response to the extra warmth in the Arctic. This slow-down of the upper-level winds circling the pole has been linked to a Hot Arctic-Cold Continents pattern that brought cold, snowy winters to the Eastern U.S. and Western Europe during 2009 - 2010 and 2010 - 2011.
Figure 3. West-to-east jet stream wind speeds at 500 mb (approximately 18,000 feet or 5,600 meters) in the mid-latitudes (40 - 60°N) over North America between 1948 and 2010. During fall (October - November - December) and winter (January - February - March), jet stream winds weakened by about 20%, from 13 - 14 m/s to 10.5 - 11 m/s. Spring (AMJ) and summer (JAS) winds changed little during this time period.
Arctic sea ice loss may increase the amplitude of jet stream troughs and ridges
The jet stream generally blows from west to east over the northern mid-latitudes, with an average position over the central U.S. in winter and southern Canada in summer. The jet stream marks the boundary between cold polar air to the north and warm subtropical air to the south, and is the path along which rain and snow-bearing low pressure systems ride. Instead of blowing straight west-to-east, the jet stream often contorts itself into a wave-like pattern. Where the jet stream bulges northwards into a ridge of high pressure, warm air flows far to the north. Where the jet loops to the south into a trough of low pressure, cold air spills southwards. The more extreme these loops to the north and south are--the amplitude of the jet stream--the slower the waves move eastward, and consequently, the more persistent the weather conditions tend to be. A high-amplitude jet stream pattern (more than 1000 miles or 1610 km in distance between the bottom of a trough and the peak of a ridge) is likely to bring abnormally high temperatures to the region under its ridge, and very cold temperatures and heavy precipitation underneath its trough. The mathematics governing atmospheric motions requires that higher-amplitude flow patterns move more slowly. Thus, any change to the atmosphere that increases the amplitude of the wave pattern will make it move more slowly, increasing the length of time extreme weather conditions persist. Dr. Francis discovered that during the early 1960s, a natural pattern in the atmosphere called the Arctic Oscillation increased the amplitude of the winter jet stream pattern over North America and the North Atlantic by more than 100 miles, increasing the potential for long-lasting weather conditions. The amplitude of the winter jet fell over 100 miles (161 km) during the late 1960s, remained roughly constant during the 1970s - 1990s, then increased by over 100 miles again during the 2000s. This latest increase in wave amplitude did not appear to be connected to the Arctic Oscillation, but did appear to be connected to the heating up of the Arctic due to sea ice loss. A warmer Arctic allows ridges of high pressure to build farther to the north. Since temperatures farther to the south near the bases of the troughs are not changing much by comparison, the result is that the amplitude of the jet stream grows as the ridges of high pressure push farther to the north. Thus it is possible that Arctic sea ice loss and the associated increases in jet stream amplitude could be partially responsible for some of the recent unusual extreme weather patterns observed in the Northern Hemisphere. This is preliminary research that has yet to be published, and much more work needs to be done before we can confidently link Arctic sea ice loss with an increase in extreme weather, though.
Figure 4. A high-amplitude jet stream pattern observed over the U.S. on December 13, 2011. Instead of blowing straight west-to-east, the jet was contorted into a southward-bulging trough of low pressure that brought cold temperatures and a snow storm to Southern California, and a northwards-bulging ridge of high pressure that brought record warm temperatures to portions of the eastern 2/3 of the country. The axis of the jet stream is marked by the strongest winds (green and light blue colors) at the top of the lower atmosphere (200 - 300 mb pressure level.)
Earlier snow cover melt on Arctic land also increases the amplitude of jet stream troughs and ridges
As Earth's climate has warmed over the past 30 years, the Northern Hemisphere has seen a dramatic drop in the amount of snow cover in spring (April, May, and June.) Spring is coming earlier by an average of three days per decade, and the earlier arrival of spring has significantly reduced the amount of snow on the ground in May. Less snow on the ground means the land surface can heat up more readily, and May temperatures in Arctic have increased significantly over the past 30 years. Dr. Francis found that the upper-level wave amplitude has increased by over 100 miles (161 km) in summer over the past decade, and this change appears to be connected to the decline in May snow cover. Thus, reduced May snow cover due to global warming may be causing higher-amplitude jet stream patterns, potentially leading to slower-moving weather patterns that favor extreme weather in summer, such as heat waves, drought, and flooding. Note that significant changes to the upper-level atmospheric circulation in spring were not observed, so springtime extreme weather events like the 2011 flooding and tornadoes in the U.S. cannot be connected to changes in the Arctic sea ice or high-latitude snow cover using this research.
Related posts
Florida shivers; Hot Arctic-Cold Continents pattern is back
Jet stream moved northwards 270 miles in 22 years; climate change to blame?
Jeff Masters
Reader Comments
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I could post more but don't want to give anyone nightmares. Some very shattering photo's coming out via twitter.
I wonder if Dr Masters will do his next blog on Washi/Sendong.
For me, looking back on hurricanes after the fact, an important part of figuring out how they work and studying them scientifically is having the most accurate description as possible.
The category system is an ok metric to say roughly what a hurricane might do, damage-wise, but it really doesn't tell you nearly as much as looking at central pressure, wind speed, integrated kinetic energy, potential storm surge, etc, etc.
Another problem with the past data is that getting accurate measurements (is/was) difficult, with many of the "recorded" results being satellite estimates based on 6 or 12 hour intervals.
And yet another issue with some of the data stems from the fact that the organization generating the data has public safety as a primary goal. The unnamed hurricane (the perfect storm) was intentionally left unclassified to not cause panic in the public. Perhaps other numbers were altered slightly due to public safety considerations? (I'm not saying this is a bad thing in general ... only bad in terms of getting scientifically accurate data).
In summary, I think what you're seeing here is some doubt of the accuracy of past measurements ... which could be for any number of reasons. At least, that's my take on it.
I find it interesting that had Floyd been 15 degrees further west, in that picture, it essentially would have been another Katrina. Practically the same size, and with the adjustment in the normal heat concentration between the Gulf and that general part of the Bahamas, essentially the same intensity.
Imo, Katrina was significant, no doubt about it, but it wasn't nearly as much of a meteorological... uniquity.. as people make it out to be. Just one of the more recent ones that people can recall.
NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOO
I've been wondering about this absolutely gorgeous weather we've been having, too, and whether we'll see a swing into massive - for Florida - cold weather in January. It would fit patterns seen in previous winters. I'm really enjoying the warm sunny weather now, as I expect it to plunge into the 50s on a regular basis. Reminder to self: look for gloves and scarf not worn for years.... lol
It's flannel weather out there right now.. anything less than 76º calls for long sleeves to a true Floridian..
That's awful about Sendong. Feared it when all that white showed up on the Rainbow loop.
Looks like they had atleast a foot of rain in the last week. Looks a little extreme in parts of China too.
Actually, I'm hoping that the sub-40s hold off until New Year's, when I'm likely to be back home. I'm likely to be in the S FL area between Christmas and New Year's, and I don't want to freeze my patooties... or my toes for that matter... :o)
I haven't looked at long range forecasts for a while, but I'd be surprised to see a major change before next weekend.
However, anything's possible in S FL... just about.
Something about the north pole??? violates community standards?
Weird.
Can't imagine to many polaar bears mad about this
Froederick :)
[and you deserve to, for not recognising the master's voice in this matter.... lol]
Wanna trade? I'd kill for a T-shirt weather!
Not quite correct. Due to the rapid melting in the arctic you will find very very very few places where the ice is 30 ft thick. The arctic survey team that went up there were drilling holes through the oldest ice areas and they were having problems finding areas deeper than 3 meters. There is very little old ice left. Warmer water temps combined with warming arctic temps have pretty much decimated the old thick ice.
New ice is ice less than 3 meters in thickness, almost all of which melts off every summer. As you noted, without thick ice around this opens up larger expanses of water, which in turn absorb a lot more energy. This makes it harder for the ice to refreeze, which in turn leads to fewer "freeze" days, and so on and so on.
The arctic has lost a lot of areal extent, but it pales in comparison to how much ice volume has been lost. If ideal melting conditions like 2007 were to happen consecutively for a few years in a row, then the arctic would be practically ice free in the summer (there would always be ice in the winter).
Awww. No white Christmas for me. :(
:)
[Sorry, couldn't resist...]
been there. comment removed for no reason
Anyway, it now seems that all is love. I am currently wondering if that ITCZ disturbance currently on track for the central American coast has even the slightest chance of impacting wx above 20N.... naw... I doubt it...
The other day some admin removed the "Twelve Days Of Christmas Wunderground version". But about 10 others had already re-posted it. That was a very funny/entertaining post and I don't don't understand how anybody (except for maybe a troll) could have found it offensive. Bizarre.
It kinda talked bad about the admins. here.
it came back....?
(NSDIC is down for routine server maintenance today till 4pm EDT)
Watch as sea ice in the Arctic ocean declines from its near-maximum state in early spring 2011 through the summer and up until Sept. 9, 2011, in this visualization of data collected by the AMSR-E instrument on NASA's Aqua satellite.
Sea ice goes through this shrink-and-swell rhythm every year, but since consistent satellite observations began in 1979, both the annual minimum at the end of summer and the annual maximum at the end of winter continue to decline in area and thickness. Consistent with rising temperatures globally and specifically in the Arctic, climate scientists are concerned with this trend both as an indicator of climate change and as a feedback mechanism. As the white, highly reflective ice disappears, darker ocean waters appear.
This darker surface absorbs more solar radiation and acts as a positive feedback to the warming that is already occurring and causing the change in the first place.
Visualization courtesy of NASA's Scientific Visualization Studio, Goddard Space Flight Center.
You can draw on it (:
I second this. It hasn't even hit the 40s at all this year in PBC and this time last year we were in the mid 20s for lows.
:OO
Neat :)
Dang it, it won't let me upload it!
UPDATE 4-Typhoon kills more than 436 in southern Philippines
* Local governments declare state of calamity
* Dozens of bodies washed ashore in nearby towns
* Houses swept into the sea while people slept
Never seen that happen before...
I'm going looking for the 12 Days of Wunderground...
Must be snowing somewhere...
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