Tropical cyclone intensity shifting poleward, study shows

May 14, 2014 by Jean Phillips
Color-enhanced infrared satellite image of Typhoon Usagi as it moved northwestward toward Hong Kong while explosively intensifying to a Category-5 storm. Usagi threatened Taiwan, the Northern Philippines, and mainland China, ultimately making landfall in eastern Guangdong province where it caused substantial flooding and more than 30 deaths. Credit: NOAA Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison

Powerful, destructive tropical cyclones are now reaching their peak intensity farther from the equator and closer to the poles, according to a new study co-authored by an MIT scientist.

The results of the study, published today in the journal Nature, show that over the last 30 years, tropical cyclones—also known as hurricanes or typhoons—are moving poleward at a rate of about 33 miles per decade in the Northern Hemisphere and 38 miles per decade in the Southern Hemisphere.

"The absolute value of the latitudes at which these storms reach their maximum intensity seems to be increasing over time, in most places," says Kerry Emanuel, an MIT professor and co-author of the new paper. "The trend is statistically significant at a pretty high level."

And while the scientists who conducted the study are still investigating the atmospheric mechanisms behind this change, the trend seems consistent with a warming climate.

"It may mean the thermodynamically favorable conditions for these storms are migrating poleward," adds Emanuel, the Cecil and Ida Green Professor of Earth and Planetary Sciences at MIT.

The implications are serious, since the movement of peak intensity means regions further north and south of the equator, which have not previously had to face many landfalls by violent cyclones, may now have greater exposure to these extreme weather events. That, in turn, could lead to "potentially profound consequences to life and property," the paper states. "Any related changes to positions where storms make landfall will have obvious effects on coastal residents and infrastructure."

Moving with the trade winds?

The paper, "The Poleward Migration of the Location of Tropical Cyclone Maximum Intensity," was co-written by Emanuel, James P. Kossin of the University of Wisconsin, and Gabriel A. Vecchi of the National Oceanic and Atmospheric Administration (NOAA).

To conduct the study, the scientists used international data from 1982 to 2012, collected by NOAA's National Climactic Data Center. They used the location of peak intensity of cyclones as a benchmark because it is a more consistent metric than statistics such as storm duration: The duration can be harder to estimate because of difficulties in establishing precisely when a storm should first be considered a tropical cyclone.

The intensity of tropical cyclones is shifting poleward, according to a new study. The latitude at which tropical storms like this achieve their greatest intensity has been shifting toward the poles and away from the tropics at an estimated rate of 33 to 39 miles per decade. The upshot may be that some areas, including densely populated coastal cities, could experience a greater risk of large storms and their associated floods and storm surges. Credit: Photo courtesy Cooperative Institute for Meteorological Satellite Studies, University of Wiscosnsin-Madison

While there are regional differences in the poleward movement of cyclones, the fact that every ocean basin other than the northern Indian Ocean has experienced this change leads the researchers to suggest, in the paper, that this "migration away from the tropics is a global phenomenon."

However, Emanuel notes, the global mechanisms underlying the trend are a matter for further research.

"We think, but have not yet been able to establish, that this is connected to independently observed poleward expansion of the Hadley circulation," Emanuel says, referring to a large-scale pattern of global winds, which in recent years has also moved further poleward. The paper notes the potential impact of vertical wind shear, which inhibits cyclone formation; data suggests a decrease in wind shear in the tropics and an increase at higher latitudes.

Emanuel notes that researchers in the field are continuing to examine the links between storm migration and global warming. Over the past three decades, the incidence of cyclones in the tropics has actually diminished—because while tropical cyclones may become more intense in a warmer climate, it is actually more difficult to generate them.

Ocean temperatures between 82 and 86 degrees Fahrenheit seem to be "ideal for the genesis of tropical cyclones," Emanuel says, "and as that belt migrates poleward, which surely it must as the whole ocean warms, the tropical cyclone genesis regions might just move with it. But we have more work to do to nail it down."

Explore further: NASA catches Gillian as a super-cyclone before quickly dissipating

More information: Paper: dx.doi.org/10.1038/nature13278

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User comments : 16

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Maggnus
4.3 / 5 (12) May 14, 2014
Just another thing predicted to be a consequence of a warming climate, as was the northward movement of the jetstream. Every day brings more evidence.
Shootist
1.6 / 5 (19) May 14, 2014
Your smarter and more knowledgeable than Dyson?

Not.

"Generally speaking, I'm much more of a conformist, but it happens I have strong views about climate because I think the majority is badly wrong, and you have to make sure if the majority is saying something that they're not talking nonsense." - Freeman Dyson
Maggnus
4.7 / 5 (13) May 14, 2014
No Shootist, I am not smarter than Dyson and I also think his caution and understanding of his own limitations makes him smarter than almost any other scientist alive right now.

The difference between him and you, however, is that he recognizes that he doesn't know, and he doesn't argue the SCIENCE! You think he is all that Shootist, so why don;t you try reading what he says IN ITS ENTIRETY instead of QUOTE MINING out of context blurbs!

Ask Freeman! He WANTS YOU TO THINK FOR YOURSELF you dimwit!
Caliban
4.7 / 5 (12) May 14, 2014
Maggnus,

You'll have to forgive shooty for not being able to distinguish been a "known unknown" and a "won'tknow don'tknown"

I wonder how many "fine" Polar Bears can fit on the shortbus with shooty?
supamark23
3.9 / 5 (12) May 14, 2014
Your smarter and more knowledgeable than Dyson?

Not.

"Generally speaking, I'm much more of a conformist, but it happens I have strong views about climate because I think the majority is badly wrong, and you have to make sure if the majority is saying something that they're not talking nonsense." - Freeman Dyson


Dude, you *do* know that Freeman Dyson accepts that AGW is a real phenomenon, right? And that he also accepts that CO2 emissions are a principal reason, right? I mean, that's actually basic physics - without a counterveiling force, increasing CO2 concentrations *must* increase avg. temperatures.
Dug
3.9 / 5 (8) May 14, 2014
There are very few large areas on the planet where water temperatures exceed 86F. Consequently, it would seem that increased global warming would increase cyclone frequency in the tropics first - and concomitantly reach peak energy levels in a growing northerly direction as the study notes. However, as yet cyclone frequency has been declining unlike climate model predicting hurricane frequency increases following the 2004 spate. There is another flawed assumption above - that the "whole ocean warms" - which isn't the case nor does it warm evenly. Interesting study and probably logically correct - at least in part - that hurricanes reach peaks energy further north as the climate warms, but three decades is hardly a climatic trend basis.
aksdad
1.4 / 5 (11) May 14, 2014
And while the scientists who conducted the study are still investigating the atmospheric mechanisms behind this change, the trend seems consistent with a warming climate.

We don't know what's causing it, but it must be global warming. Brilliant.

Later on, Emanuel says:
the global mechanisms underlying the trend are a matter for further research.

So who concluded that it's "consistent with a warming climate", the scientists or the author of the blog post?

You see, meteorologists understand that tropical cyclones require a significant difference between sea surface and atmospheric temperatures to form. Tropical cyclones tend to form during the part of the year when those temperature differences are greatest.

So how is global warming causing tropical cyclones to shift poleward? Is the average temperature gradient between ocean surface and atmosphere shifting poleward? Are equatorial temperatures becoming more uniform? Please explain.
aksdad
1.4 / 5 (11) May 14, 2014
I don't know if you noticed, Maggnus, but the news for 2013 was record cold temperatures for most of the U.S. because the jet stream dipped southward. Remember all that talk about circumpolar vortex?

The IPCC Fifth Assessment Report (Ch. 14, pg. 1220) does make some qualified predictions about the jet stream and tropical cyclones migrating poleward. Interestingly, those predictions are based not on any understood mechanism driven by global warming, but based on observed trends for the last 3 or 4 decades.

In other words, studies noticed a slight migration trend over the last 30 to 40 years, so they predict it will continue. IPCC AR5 candidly admits they don't understand the connection between warming and poleward migration of the jet stream or tropical cyclones. So much for "another thing predicted to be a consequence of a warming climate."
Caliban
4.6 / 5 (10) May 14, 2014
"I don't know if you noticed, Maggnus, but the news for 2013 was record cold temperatures for most of the U.S. because the jet stream dipped southward. Remember all that talk about circumpolar vortex?


And were you aware, sksnads, that the pacific coast and part of SWUS was above average temp during that time? "Remember all that talk about circumpolar vortex?"

BOTH extremes are expected(and yes, even simultaneously) as the Polar Vortex/Jet Stream respond to GW.

Moron.
Caliban
4.5 / 5 (8) May 14, 2014


In other words, studies noticed a slight migration trend over the last 30 to 40 years, so they predict it will continue. IPCC AR5 candidly admits they don't understand the connection between warming and poleward migration of the jet stream or tropical cyclones. So much for "another thing predicted to be a consequence of a warming climate."


And this observation of yours is also complete horseshit.

These changes are to be expected as a result of heat being added into the Earth's surface fluid hydrodynamics --aka atmosphere/aquasphere. That's why the changes have already been observed to match up with past "predictions".

Moron.

tdw
1.5 / 5 (8) May 14, 2014
No Shootist, I am not smarter than Dyson and I also think his caution and understanding of his own limitations makes him smarter than almost any other scientist alive right now.

The difference between him and you, however, is that he recognizes that he doesn't know, and he doesn't argue the SCIENCE! You think he is all that Shootist, so why don;t you try reading what he says IN ITS ENTIRETY instead of QUOTE MINING out of context blurbs!

Ask Freeman! He WANTS YOU TO THINK FOR YOURSELF you dimwit!


Uh, actually he does argue the science. He point is that we do not know how to model climate so any claims about global warming are baseless.
tdw
1.5 / 5 (8) May 14, 2014
"increasing CO2 concentrations *must* increase avg. temperatures.


By how much?

http://hockeyscht...ate.html
http://hockeyscht...-to.html
http://hockeyscht...-to.html
cantdrive85
2 / 5 (8) May 15, 2014
So much for "another thing predicted to be a consequence of a warming climate."

He is without compunction in regards to lying or fallacious argument, it's his M.O.
PinkElephant
4.6 / 5 (9) May 15, 2014
@stupid & co.,
So much for "another thing predicted to be a consequence of a warming climate."

He is without compunction in regards to lying or fallacious argument, it's his M.O.
So here's one sample dose of REALITY for you:
http://www.math.u...7_1e.pdf
To quote,
Ground-based and satellite instrumental data together provide evidence that the Hadley cells have expanded poleward by about 2 to 4.5 degrees of latitude in the past 27 years, and their circulation velocity is decreasing [3,7,19,20]. **GCM simulations forecast that this poleward expansion of the Hadley cells, together with a slowing of their circulation, will continue throughout this century [16,24]** ... The details of the mechanisms causing this widening of the tropical belt are not yet fully understood. ... the observed widening is occurring even faster than **predicted by the suite of IPC models**.
So: predicted by models, but **exact** dynamics are still TBD.
Captain Stumpy
4.5 / 5 (8) May 15, 2014
I don't know if you noticed, Maggnus, but the news for 2013 was record cold temperatures for most of the U.S. because the jet stream dipped southward
@aksdud
and your assumption is that warming had nothing to do with it? watch the video in this link: http://qz.com/163...n-worse/

@stupid & co.,
@PinkElephant
good luck educating Cant-think-or-read... he is an EU acolyte. He will not believe in anything outside his delusional world, and he is almost as contrarian as rygg (and every bit as smart). Even in the face of empirical data/proof he still clings to things like electric formation of the grand canyon and craters on Mars/Moon as well as the electric sun etc
runrig
4.5 / 5 (8) May 15, 2014
So how is global warming causing tropical cyclones to shift poleward? Is the average temperature gradient between ocean surface and atmosphere shifting poleward? Are equatorial temperatures becoming more uniform? Please explain.


Ask...
OK, I will.
THE only thing, when traced to first principles, that could shift storm positions poleward, IS warming temps.
It is the (tropospheric) temp gradient that gives rise to winds aloft and given that the poles (chiefly the NP - due the incredible geography of Antarctica) will warm more, the zone of greatest baroclinicity will move north (talking just of the NH) as a result.
Yes, Tropical storms/Hurricanes/Typhoons/Cyclones generate their energy from the latent heat release of condensing WV from those very warm seas .... but they need a certain configuration of winds aloft of them to "trigger" the storm. That is a divergence aloft (sucking). This would naturally follow with the poleward movement of the strongest winds aloft.

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