Dartmouth Engineer - The Magazine of Thayer School of EngineeringDartmouth Engineer - The Magazine of Thayer School of Engineering

The Space Weathermen

Space weather researchers William Lotko and Simon Shepherd want to help protect the technological world from solar storms.

By Anna Fiorentino

If meteorologists could have predicted the exact path and strength of Hurricane Sandy, more people might have moved their families and possessions to safer ground.

Similarly, if scientists like Professors William Lotko and Simon Shepherd could forecast the path of radiation hurled into space by solar storms, operators of satellites, spacecraft, planes, and various other vulnerable technological systems could adapt as needed.

Professors William Lotko and Simon Shepherd, left to right
EYES ON THE SKY: Professors William Lotko and Simon Shepherd, left to right, are developing better ways to forecast solar storms. Photograph by Liza Chrust.

Solar storms may look beautiful—they produce the Northern and Southern Lights—but they have the power to wreak havoc on and above Earth. Unleashing enormous amounts of plasma and electromagnetic energy, solar flares and coronal mass ejections (CME) can jeopardize the health of astronauts in space and crews aboard aircraft, damage satellites, and disrupt GPS signals. The largest CMEs—huge squall fronts in the solar wind that warp and puncture the magnetosphere, the protective magnetic cocoon surrounding Earth—can knock out the electric grid, corrode oil and gas pipelines, and cause other technological troubles on Earth.

“When a CME with the right characteristics impacts geospace, electrons and protons permeating the magnetosphere are accelerated to relativistic energies and transported into the hazardous Van Allen radiation belts,” says Lotko. “These charged particles behave like pebbles in a slingshot with the energy in the extended rubber band going into the rock when the slingshot—the stretched magnetic field—is released.”

Although scientists are far ahead of where they once were in predicting when these events will take place—on spaceweather.com anyone can find out if a solar storm is on its way—there is much more to understand.

“People already know when the storm is coming, based on observing explosions on the sun,” says Shepherd. “But because a CME usually takes several days to get here, distortions happen along the way that complicate factors, like the amount of mass, the speed, and orientation of the sun’s magnetic field.”

Both Shepherd and Lotko are probing such complexities at a particularly relevant time: a solar maximum. “Right now we’re entering a period where more sunspots are occurring, so you’re more likely to see a massive solar storm,” says Shepherd. “An apocalyptic solar storm might happen every few hundred years, with a few ‘superstorms’ occurring every solar cycle, approximately every 11 years.”

During the largest recorded solar storm, the Carrington Event of 1859, a CME reached Earth in 17 hours instead of a few days. Aurorae were seen across the world, and telegraph systems caught fire because of the huge currents flowing in the wires. In 1989 a huge CME knocked out power for 6 million people in Quebec.

With enough advance notice of bursts of solar radiation, people could shut down sensitive equipment in satellites, change load distributions in power lines, reroute power on the electric grid to lower latitudes, and siphon off electrical currents from pipelines. Astronauts could avoid space walks and retreat into the most shielded interior spaces of spacecraft. Airlines could steer clear of polar regions to minimize crew and passenger exposure to radiation.

Lotko and Shepherd are working on ways to extend the window of advance warning.


Modeling Space Weather

A coronal mass ejection explodes from the sun
SOLAR STORM: A coronal mass ejection explodes from the sun. Photograph courtesy of NASA/Solar Dynamics Observatory.

Lotko is working on a forecasting model to predict the impacts of solar flares and CMEs. “The National Weather Service tracks the disturbances leaving the sun and tries to forecast their path and impacts on the near-Earth space environment. At Dartmouth, we are developing numerical prediction models to improve their forecasting ability,” he says.

There’s not much time to stay ahead of solar flares, which reach Earth’s upper atmosphere and ionosphere in just eight minutes. And although it usually takes two to four days for an enormous CME to reach Earth, current tracking techniques only give forecasters 30 to 60 minutes advance notice to infer the impact.

The limitations are due in part to the fact that data come from a single source, a NASA satellite at a location known as L1, where the gravitational pull of the sun and Earth are equal and opposite. “We use measured characteristics of the solar wind at L1 to initialize global simulation models to predict likely effects on geospace or to verify that our models give results similar to what actually happened,” Lotko says. Eventually he and his colleagues hope to use information derived from optical measurements of the sun to initialize simulation models—and produce a longer forecasting window of two to four days.

Lotko’s model focuses on how energy dynamics in the magnetosphere and ionosphere affect each other. The work is helping to advance and expand a model launched in 1987 by Dartmouth physics professor John Lyon that provides a self-consistent physical description of the global magnetosphere. Still being refined by Lyon, Lotko, and others, the Lyon-Fedder-Mobarry (LFM) model currently includes more physics and thus produces more precise diagnostics than the seven other models under development worldwide. It is being evaluated for use by the National Oceanic and Atmospheric Administration and National Weather Service.

Two of Lotko’s recent Ph.D. students, Oliver Brambles Th’12 and Bin Zhang Th’12, used the LFM model to resolve a 20-year-old mystery: why the entire geospace environment sometimes goes into a three-hour “sawtooth” oscillation. “Bin augmented the LFM simulation model to include intense flows of electromagnetic power into the Earth’s upper atmosphere during geomagnetic activity, and Oliver used Bin’s electromagnetic power to drive the massive outflows of atmospheric oxygen ions into geospace that excite the sawtooth mode,” says Lotko. “Before their work, no one imagined that oxygen ion outflows could produce such an effect. It’s a brilliant example of research in ‘Pasteur’s Quadrant’—discovery science motivated by practical application.”

Lotko regularly collaborates on NSF-funded space weather modeling with colleagues from Johns Hopkins University and Colorado’s National Center for Atmospheric Research. Since 1992 he has led Dartmouth’s NASA-funded Heliophysics Theory Project, aimed at understanding how ions that flow from the ionosphere to the magnetosphere are energized. Lotko also collaborates with his wife, Dartmouth physics professor Mary Hudson, and John Lyon on the NSF-funded Center for Integrated Space Weather Modeling based at Boston University.

“I’ve always had an interest in electromagnetic fields and in fluid mechanics, even as an undergraduate. Space weather merges my background in plasma physics and hydrodynamics, which are also useful in describing thermonuclear fusion reactions and processes that occur in the stars and sun,” says Lotko. “But in contrast to solar physics and astrophysics, I gravitated toward geospace weather for its social relevance. We need these models to predict the effect solar flares and CMEs have on satellite operations as we become a more technology-reliant society.”


Measuring Auroral Activity

Auroral displays are visible manifestations of space weather
STUNNING EVIDENCE: Auroral displays are visible manifestations of space weather. Photograph by David Cartier Sr.

Shepherd is part of an international team of about 100 scientists and engineers using ground-based radars to measure the drifts of plasma in the mid- and high-latitude regions of Earth’s ionosphere. This group, using the Super Dual Auroral Radar Network, or SuperDARN, is looking to better predict the effects of solar disturbances and CMEs on the ionosphere—the electrically conducting layer above the Earth that facilitates the propagation of radio waves for very long distances. SuperDARN is a term coined by Raymond Greenwald, who earned his Ph.D. in physics from Dartmouth in 1970 and a decade later pioneered the technique and design of these radars.

Today the SuperDARN project consists of more than 30 ground-based radars operated by more than a dozen countries in the Northern and Southern hemispheres. The radars are directed toward polar latitudes to measure the motion of the plasma, the ionized matter that fills more than 99 percent of space, at ionospheric altitudes greater than 100 kilometers above Earth. Each radar in the network is capable of transmitting roughly 10 kilowatts of radio wave power that can travel several thousand kilometers before reflecting off irregularities in the density of the plasma. “The frequency of the return signal is Doppler-shifted according to the speed of the plasma, so we can measure the motion of the plasma over a very large area,” says Shepherd. “The system works similarly to a weather Doppler radar, except that we use a lower frequency, radio waves travel farther, and they reflect off the plasma rather than rain, snow, or sleet.” The radars are situated to make observations in the polar regions, where converging magnetic fields focus the effects of coupling to the solar wind most strongly.

In 2008 Shepherd and his former fellow postdocs under Greenwald at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) received an NSF grant to build eight radars at four mid-latitude locations: Kansas, Oregon, the Aleutian Islands, and the Azores, worth a combined $6 million. Shepherd and the researchers from Virginia Tech, the University of Alaska, Fairbanks and JHU/APL have built six of these radars so far—extending the mid-latitude network of SuperDARN radars already in Virginia and Japan. Coupled with existing high-latitude arrays, the radars will measure drifting plasma in the ionosphere over a region stretching from Eastern Asia to Europe and from Kansas to the magnetic North Pole. Of particular importance, the mid-latitude radars will be able to track the movement of plasma into lower latitudes during geomagnetic storms.

Shepherd, who earned his Ph.D. in physics at Dartmouth in 1998, helped build two radar arrays in Kansas before leading construction of two arrays in central Oregon. He recently helped build another pair of radars in remote Adak, Alaska. Components for the final pair of radars, slated for installation this year on the island of Graciosa, Azores, are being fabricated in Shepherd’s Thayer laboratory with the help of Dartmouth undergraduates.

“We work unbelievable hours just to build these things,” he says, although he admits, “I enjoy the physical labor.”

Of course, building the radar arrays is just the beginning. Thayer hosts tens of terabytes of radar data that are regularly analyzed by Shepherd and his students in order to develop more accurate models of the large-scale motion of the plasma in the polar ionosphere.

Ellen Cousins ’08 Th’12 helped Shepherd on several radar builds during her doctoral studies. “It’s cool to think that I helped build something that now provides data to scientists across the world,” she says. Cousins, now a postdoc at the National Center for Atmospheric Research, uses SuperDARN data to examine high-latitude plasma drifts. “I like that space weather is a relatively small and new field, which means there are still a lot of unanswered questions,” she says.

Questions about space weather have a growing sense of urgency.

“You know what it’s like when a meteorologist misses a regular weather forecast,” says Shepherd. “Well up there, multimillion-dollar satellites orbiting the Earth have been rendered inoperable—and we are becoming more reliant on these types of satellites every day.”

—Anna Fiorentino is senior writer at Dartmouth Engineer.

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