Image of the Day: Krypton-dating technique allows researchers to accurately date ancient Antarctic ice

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A team of scientists, funded by the National Science Foundation (NSF), has successfully used a new technique to confirm the age of a 120,000-year-old sample of Antarctic ice. The new dating system is expected to allow scientists to identify ice that is much older, thereby reconstructing climate much farther back into Earth’s history and potentially leading to an understanding of the mechanisms that cause the planet to shift into and out of ice ages. The new technique provides an accurate means of confirming the age of ice samples, and researchers note it is now the most precise dating tool for ancient ice.

Image credit: Hinrich Schaefer

Image of the Day: Old tires become material for new and improved roads

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Americans generate nearly 300 million scrap tires every year, according to the Environmental Protection Agency (EPA). Historically, these worn tires often end up in landfills or, when illegally dumped, become breeding grounds for disease-carrying mosquitoes and rodents. They also pose a potential fire hazard. In recent years, however, interest has been growing in finding new, beneficial and environmentally friendly uses for discarded tires. Magdy Abdelrahman, for example, an associate professor of civil and environmental engineering at North Dakota State University, is working on ways to turn old tires into new and improved roads. The National Science Foundation-funded scientist is experimenting with “crumb” rubber–ground up tires of different sized particles–and other components to improve the rubberized road materials that a number of states already are using to enhance aging asphalt. Asphalt rubber binders (like the sample pictured here) can be used as traditional binders with no particle-related concerns.

Image credit: Magdy Abelrahman

A river of plasma, guarding against the sun

The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

Mapping Earth’s magnetic shield

For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

A river of plasma

Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

“I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

By Jennifer Chu, MIT News Office

A river of plasma, guarding against the sun

The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

Mapping Earth’s magnetic shield

For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

A river of plasma

Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

“I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

By Jennifer Chu, MIT News Office

3 Questions: Michael Greenstone on the experimental method in environmental economics

How can scholars get traction on environmental problems, particularly those relating to pollution? In an essay appearing in this week’s issue of the journal Science, MIT economist Michael Greenstone, along with co-authors Francesca Dominici and Cass Sunstein of Harvard University, make the case for “quasi-experiments,” or “natural experiments,” which have gained prominence in other domains of the social sciences. Environmental economics, they suggest, can rely increasingly on quasi-experiments to sharpen its conclusions about which kinds of environmental action are most cost-effective. Greenstone sat down with MIT News to discuss the subject.

Q. Why should quasi-experiments be in the environmental economics toolbox?

A. The single best way to learn about the world is through randomized controlled trials (RCTs). Now, some problems are not directly amenable to RCTs. In the case of climate change, we don’t have a second planet to randomly assign climate change to, or not. And that means to learn about a lot of environmental problems, such as climate change or air quality, we have to turn to other methods.

The conventional approach to doing that has been to rely on comparisons of places that are more polluted to places that are less polluted. [But] places that are more polluted might have other things that are different about them, besides the pollution. In this paper we have highlighted a potential solution, the use of quasi-experimental evaluation techniques, which mimic some of the features of an experiment, in the sense that there is a group that receives the treatment and a [very similar] group that doesn’t. But [this] is based on nature or politics or some other accident, rather than being done through random assignment.

In the case of environmental questions, there has been great progress in the last 10 to 15 years applying quasi-experiments to environmental questions. This same revolution has been occurring in other fields — labor economics, development economics, public finance, statistics, and criminology. This “credibility revolution,” as some people refer to it, tries to move beyond simple comparisons.

Q. What are some kinds of topics or findings that attest to the value of quasi-experiments in environmental economics?

A. One is a comparison of what happened to air pollution-related diseases during the Beijing Olympics, when the Chinese government shut down, by fiat, many sources of air pollution. Others have been taking advantage of the way the Clean Air Act was implemented in the U.S., using places that were otherwise similar, some of which were regulated stringently and others were much less so, [and measuring] what happens to air quality, infant mortality rates, housing prices, and manufacturing activity in those places.

More recently I [co-authored] a paper [with Yuyu Chen, Avraham Ebenstein, and Hongbin Li], on air pollution and life expectancy, by looking at a region in China where there were very large increases in particulate air pollution relative to otherwise seemingly similar places. If you go back to the planning period in China, they didn’t have enough money to heat all of China during the winter, so they implemented an arbitrary rule, which is often the hallmark of quasi-experiments. This arbitrary rule was that all places north of the Huai River were to receive free winter heating, largely derived from coal combustion, and in places to the south, no heating was allowed.

The first result of that paper is that there are dramatic differences in particulate air pollution [between the] north and south [sides] of the river, due to the Huai River heating policy. The second result is: That appears to be matched by sharp declines in life expectancy, just to the north of the river, and just to the south. If you were unfortunate enough to be an intended beneficiary of this policy, the consequences appear substantial: The people who live to the north have a life expectancy of about five years less than people just to the south. If you took those estimates literally, it would suggest the half a billion people in the north are losing 2.5 billion years of life expectancy, which is a staggering figure.

There is another remarkable thing about particulates that motivated us to write the Science paper: We just went back into old [Office of Management and Budget] reports on the benefits of regulation, and somewhere between one-third and one-half of all benefits from all regulations come from the regulation of pollution — and one [form of] air pollution in particular, particulates in air pollution.

Q. When we talk about cost-benefits analyses regarding health, it can create trepidation among those who think focusing on limiting costs may lead to less emphasis on benefits. Quasi-experiments may be sharper tools, but are they also policy-neutral in this sense?

A. Let’s start with the [opposite] case, where we rule out quantitative analysis as being too easily politicized. I think what happens in that vacuum is that people with vested interests rush in. And by definition they do not have the welfare of the full country at heart; they have the welfare of the interest groups or businesses they’re running or representing, be they pro-environment or anti-environment. And I think quantification is absolutely central to being able to constrain those arguments. There is no question that quantification can be abused like anything else can be abused. But I think the role of the university and the academy is to put out, as best they can, credible answers, and what I have observed in the political process is that high-level academic research does not always drive policy decisions, but it puts bounds on the policy discussion. Those bounds constrain the policy decisions to a region around the best evidence. And that can be very valuable.

By Peter Dizikes | MIT News Office

3 Questions: Michael Greenstone on the experimental method in environmental economics

How can scholars get traction on environmental problems, particularly those relating to pollution? In an essay appearing in this week’s issue of the journal Science, MIT economist Michael Greenstone, along with co-authors Francesca Dominici and Cass Sunstein of Harvard University, make the case for “quasi-experiments,” or “natural experiments,” which have gained prominence in other domains of the social sciences. Environmental economics, they suggest, can rely increasingly on quasi-experiments to sharpen its conclusions about which kinds of environmental action are most cost-effective. Greenstone sat down with MIT News to discuss the subject.

Q. Why should quasi-experiments be in the environmental economics toolbox?

A. The single best way to learn about the world is through randomized controlled trials (RCTs). Now, some problems are not directly amenable to RCTs. In the case of climate change, we don’t have a second planet to randomly assign climate change to, or not. And that means to learn about a lot of environmental problems, such as climate change or air quality, we have to turn to other methods.

The conventional approach to doing that has been to rely on comparisons of places that are more polluted to places that are less polluted. [But] places that are more polluted might have other things that are different about them, besides the pollution. In this paper we have highlighted a potential solution, the use of quasi-experimental evaluation techniques, which mimic some of the features of an experiment, in the sense that there is a group that receives the treatment and a [very similar] group that doesn’t. But [this] is based on nature or politics or some other accident, rather than being done through random assignment.

In the case of environmental questions, there has been great progress in the last 10 to 15 years applying quasi-experiments to environmental questions. This same revolution has been occurring in other fields — labor economics, development economics, public finance, statistics, and criminology. This “credibility revolution,” as some people refer to it, tries to move beyond simple comparisons.

Q. What are some kinds of topics or findings that attest to the value of quasi-experiments in environmental economics?

A. One is a comparison of what happened to air pollution-related diseases during the Beijing Olympics, when the Chinese government shut down, by fiat, many sources of air pollution. Others have been taking advantage of the way the Clean Air Act was implemented in the U.S., using places that were otherwise similar, some of which were regulated stringently and others were much less so, [and measuring] what happens to air quality, infant mortality rates, housing prices, and manufacturing activity in those places.

More recently I [co-authored] a paper [with Yuyu Chen, Avraham Ebenstein, and Hongbin Li], on air pollution and life expectancy, by looking at a region in China where there were very large increases in particulate air pollution relative to otherwise seemingly similar places. If you go back to the planning period in China, they didn’t have enough money to heat all of China during the winter, so they implemented an arbitrary rule, which is often the hallmark of quasi-experiments. This arbitrary rule was that all places north of the Huai River were to receive free winter heating, largely derived from coal combustion, and in places to the south, no heating was allowed.

The first result of that paper is that there are dramatic differences in particulate air pollution [between the] north and south [sides] of the river, due to the Huai River heating policy. The second result is: That appears to be matched by sharp declines in life expectancy, just to the north of the river, and just to the south. If you were unfortunate enough to be an intended beneficiary of this policy, the consequences appear substantial: The people who live to the north have a life expectancy of about five years less than people just to the south. If you took those estimates literally, it would suggest the half a billion people in the north are losing 2.5 billion years of life expectancy, which is a staggering figure.

There is another remarkable thing about particulates that motivated us to write the Science paper: We just went back into old [Office of Management and Budget] reports on the benefits of regulation, and somewhere between one-third and one-half of all benefits from all regulations come from the regulation of pollution — and one [form of] air pollution in particular, particulates in air pollution.

Q. When we talk about cost-benefits analyses regarding health, it can create trepidation among those who think focusing on limiting costs may lead to less emphasis on benefits. Quasi-experiments may be sharper tools, but are they also policy-neutral in this sense?

A. Let’s start with the [opposite] case, where we rule out quantitative analysis as being too easily politicized. I think what happens in that vacuum is that people with vested interests rush in. And by definition they do not have the welfare of the full country at heart; they have the welfare of the interest groups or businesses they’re running or representing, be they pro-environment or anti-environment. And I think quantification is absolutely central to being able to constrain those arguments. There is no question that quantification can be abused like anything else can be abused. But I think the role of the university and the academy is to put out, as best they can, credible answers, and what I have observed in the political process is that high-level academic research does not always drive policy decisions, but it puts bounds on the policy discussion. Those bounds constrain the policy decisions to a region around the best evidence. And that can be very valuable.

By Peter Dizikes | MIT News Office

Image of the Day: Global perspectives on a comet

Full Text:

Photographers from around the globe received awards for their stunning images of comet C/2012 S1 (ISON) at the Northeast Astronomy Forum held at Rockland Community College recently. The National Science Foundation’s Division of Astronomical Sciences, Astronomy magazine and Discover magazine co-sponsored the photo contest.
Shown here is People’s Choice award winner Eric Cardoso’s photo, “Comet ISON,” from Setúbal, Portugal.

Image credit: Eric Cardoso

3 Questions: Michael Greenstone on the experimental method in environmental economics

How can scholars get traction on environmental problems, particularly those relating to pollution? In an essay appearing in this week’s issue of the journal Science, MIT economist Michael Greenstone, along with co-authors Francesca Dominici and Cass Sunstein of Harvard University, make the case for “quasi-experiments,” or “natural experiments,” which have gained prominence in other domains of the social sciences. Environmental economics, they suggest, can rely increasingly on quasi-experiments to sharpen its conclusions about which kinds of environmental action are most cost-effective. Greenstone sat down with MIT News to discuss the subject.

Q. Why should quasi-experiments be in the environmental economics toolbox?

A. The single best way to learn about the world is through randomized controlled trials (RCTs). Now, some problems are not directly amenable to RCTs. In the case of climate change, we don’t have a second planet to randomly assign climate change to, or not. And that means to learn about a lot of environmental problems, such as climate change or air quality, we have to turn to other methods.

The conventional approach to doing that has been to rely on comparisons of places that are more polluted to places that are less polluted. [But] places that are more polluted might have other things that are different about them, besides the pollution. In this paper we have highlighted a potential solution, the use of quasi-experimental evaluation techniques, which mimic some of the features of an experiment, in the sense that there is a group that receives the treatment and a [very similar] group that doesn’t. But [this] is based on nature or politics or some other accident, rather than being done through random assignment.

In the case of environmental questions, there has been great progress in the last 10 to 15 years applying quasi-experiments to environmental questions. This same revolution has been occurring in other fields — labor economics, development economics, public finance, statistics, and criminology. This “credibility revolution,” as some people refer to it, tries to move beyond simple comparisons.

Q. What are some kinds of topics or findings that attest to the value of quasi-experiments in environmental economics?

A. One is a comparison of what happened to air pollution-related diseases during the Beijing Olympics, when the Chinese government shut down, by fiat, many sources of air pollution. Others have been taking advantage of the way the Clean Air Act was implemented in the U.S., using places that were otherwise similar, some of which were regulated stringently and others were much less so, [and measuring] what happens to air quality, infant mortality rates, housing prices, and manufacturing activity in those places.

More recently I [co-authored] a paper [with Yuyu Chen, Avraham Ebenstein, and Hongbin Li], on air pollution and life expectancy, by looking at a region in China where there were very large increases in particulate air pollution relative to otherwise seemingly similar places. If you go back to the planning period in China, they didn’t have enough money to heat all of China during the winter, so they implemented an arbitrary rule, which is often the hallmark of quasi-experiments. This arbitrary rule was that all places north of the Huai River were to receive free winter heating, largely derived from coal combustion, and in places to the south, no heating was allowed.

The first result of that paper is that there are dramatic differences in particulate air pollution [between the] north and south [sides] of the river, due to the Huai River heating policy. The second result is: That appears to be matched by sharp declines in life expectancy, just to the north of the river, and just to the south. If you were unfortunate enough to be an intended beneficiary of this policy, the consequences appear substantial: The people who live to the north have a life expectancy of about five years less than people just to the south. If you took those estimates literally, it would suggest the half a billion people in the north are losing 2.5 billion years of life expectancy, which is a staggering figure.

There is another remarkable thing about particulates that motivated us to write the Science paper: We just went back into old [Office of Management and Budget] reports on the benefits of regulation, and somewhere between one-third and one-half of all benefits from all regulations come from the regulation of pollution — and one [form of] air pollution in particular, particulates in air pollution.

Q. When we talk about cost-benefits analyses regarding health, it can create trepidation among those who think focusing on limiting costs may lead to less emphasis on benefits. Quasi-experiments may be sharper tools, but are they also policy-neutral in this sense?

A. Let’s start with the [opposite] case, where we rule out quantitative analysis as being too easily politicized. I think what happens in that vacuum is that people with vested interests rush in. And by definition they do not have the welfare of the full country at heart; they have the welfare of the interest groups or businesses they’re running or representing, be they pro-environment or anti-environment. And I think quantification is absolutely central to being able to constrain those arguments. There is no question that quantification can be abused like anything else can be abused. But I think the role of the university and the academy is to put out, as best they can, credible answers, and what I have observed in the political process is that high-level academic research does not always drive policy decisions, but it puts bounds on the policy discussion. Those bounds constrain the policy decisions to a region around the best evidence. And that can be very valuable.

By Peter Dizikes | MIT News Office

A river of plasma, guarding against the sun

The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

Mapping Earth’s magnetic shield

For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

A river of plasma

Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

“I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

By Jennifer Chu, MIT News Office

Image of the Day: ALMA sees a baby solar system

Full Text:

Observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope of the disc of gas and cosmic dust around the young star HD 142527 show vast streams of gas flowing across the gap in the disc. These are created by giant planets guzzling gas as they grow. The dust in the outer disc is shown in red. Dense gas in the streams flowing across the gap, as well as in the outer disc, is shown in green. Diffuse gas in the central gap is shown in blue. The gas filaments can be seen at the three o’clock and ten o’clock positions, flowing from the outer disc towards the center.

Image credit: ALMA (ESO/NAOJ/NRAO), S. Casassus et al.

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