Tropical cyclone Usagi intensity shifting poleward

Colour-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 favourable 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."

Hadley Cells

"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.

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

NASA IBEX: Interstellar winds buffeting our solar system have shifted direction

This image shows the nearest interstellar gas clouds around the solar system, including the Local Interstellar Cloud (LIC) and G Cloud, along with positions of neighboring stars in the plane of our Milky Way galaxy. 

The arrow shows the sun's motion relative to neighboring stars. 

Image courtesy of P.C. Frisch, University of Chicago

Scientists, including University of New Hampshire astrophysicists involved in NASA's Interstellar Boundary Explorer (IBEX) mission, have discovered that the particles streaming into the solar system from interstellar space have likely changed direction over the last 40 years.

The finding helps scientists map our location within the Milky Way galaxy and is crucial for understanding our place in the cosmos through the vast sweep of time—where we've come from, where we're currently located, and where we're going in our journey through the galaxy.

Additionally, scientists now gain deeper insight into the dynamic nature of the interstellar winds, which has major implications on the size, structure, and nature of our sun's heliosphere—the gigantic bubble that surrounds our solar system and helps shield us from dangerous incoming galactic radiation.

The results, based on data spanning four decades from 11 different spacecraft, including IBEX, were published in the journal Science September 5, 2013.

Eberhard Möbius

"It was very surprising to find that changes in the interstellar flow show up on such short time scales because interstellar clouds are astronomically large," says Eberhard Möbius, UNH principal scientist for the IBEX mission and co-author on the Science paper.

Adds Möbius, "However, this finding may teach us about the dynamics at the edges of these clouds—while clouds in the sky may drift along slowly, the edges often are quite fuzzy and dynamic. What we see could be the expression of such behaviour."

The data from the IBEX spacecraft show that neutral interstellar atoms are flowing into the solar system from a different direction than previously observed.

Interstellar atoms flow past the Earth as the interstellar cloud surrounding the solar system passes the sun at 23 kilometers per second (50,000 miles per hour).

The various sets of observations relied on three different methods to measure the incoming interstellar wind. IBEX and Ulysses directly measured neutral helium atoms as they coursed through the inner solar system.

IBEX's measurements are close to Earth, while Ulysses' measurements were taken between 1.3 and 2 times further from the sun.

Nathan Schwadron

In the final analysis, the direction of the wind obtained most recently by IBEX data differs from the direction obtained from the earlier measurements, which strongly suggests the wind itself has changed over time.

"Prior to this study, we were struggling to understand why our current measurements from IBEX differed from those of the past," says co-author Nathan Schwadron, lead scientist for the IBEX Science Operations Center at UNH.

"We are finally able to resolve why these fundamental measurements have been changing with time: we are moving through a changing interstellar medium."

More information: "Decades-Long Changes of the Interstellar Wind Through Our Solar System," by P.C. Frisch et al Science, 2013.