ECE: Electrical & Computer Engineering
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Special Feature: SPACE WEATHER

SuperDARN
It's Raining Plasma

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Those ionospheric plasma winds are blowing up a storm

Plasma

ECE's newest laboratory stretches thousands of kilometers into the ionosphere from a field near Blackstone, Va.. The HokieDARN radar enables first-time-ever, continual mapping of space weather plasma motions over the northern United States and southern Canada.

HokieDARN is the newest part of the Super Dual Auroral Radar Network (SuperDARN) which is an international collaboration involving a dozen countries. High frequency radars are positioned around the world and operated continuously to provide the only method of obtaining global, instantaneous maps of plasma convection.

Blackston SuperDARN

The Blackstone SuperDARN field-of-view plot.

"The ionosphere is like a CRT; it projects a picture of what is happening in Earth's near-space environment," explains Michael Ruohoniemi, who is on the SuperDARN project. "We can see motions in the plasma in the ionosphere that resemble winds. When we combine the measurements from all the radars, we generate something that looks like a familiar weather map, only the speeds reach thousands of miles per hour and change in a few seconds.

Scientists around the world use SuperDARN data to help understand the many effects of space weather, according to Joseph Baker, who is also a SuperDARN team member. "The Earth's magnetic field is like wires that transfer the energy from the solar wind into the upper atmosphere," he explains. "When the near-Earth space environment (or magnetosphere) gets stressed, it corrects by dumping energy into the atmosphere via the auroras and heating from powerful electric currents."

SuperDARN was first built in the 1990s as a chain of radars ringing the auroral latitudes and pointing towards the poles. "We wanted to study the auroral processes that occur daily and their connection to the solar wind," Ruohoniemi says. The SuperDARN efforts succeeded in producing the first-ever direct two-dimensional images of convection on global spatial scales. The resulting discoveries touched on the complementary nature of convection in the northern and southern hemispheres, the occurrence of hurricane-like vortices in the plasma flow, and the rapid response of convection to change in the solar wind.

Until recently the mapping was available only for the far northern and southern latitudes. This is sufficient for studying such phenomena as the magnetospheric substorm, which occurs frequently and is mostly confined to auroral latitudes. Powerful magnetic storms, however, which occur much less often but have more serious effects, trigger very large disturbances in the space environment and can even cause auroras to be seen as far south as Texas.

The HokieDARN radar

The Blackstone SuperDARN field-of-view plot.

"These events are big and dramatic &mdash and can be dangerous for people flying over the poles in aircraft, for astronauts, for GPS and other communication and radar systems," Ruohoniemi says. "The impacts get even more significant at the mid-latitudes since more people live there and the density of vulnerable technology is greater.

The original SuperDARN radars were pointed towards the poles and were missing the expansion of such large events. The SuperDARN collaborators decided to begin installation of a chain of mid-latitude radars, which is sometimes referred to as StormDARN, to study the magnetic storm electric fields. The first mid-latitude system was built in 2005 at Wallops Island, Va., by the Johns Hopkins Applied Physics Laboratory (JHU/APL) and NASA Goddard Space Flight Center (NASA/ GSFC).

The targets for the radar system are plasma irregularities in the ionosphere that often cause problems with other systems, such as GPS, surveillance radars, and HF communications. "It is a case of one guy's noise becoming another guy's signal," describes Baker. With the mid-latitude data, scientists were able to continuously monitor both storm and quiet time activity over a larger area. "We quickly mapped the expansion of storm-time electric fields from the auroral zone to mid-latitudes with the Wallops radar and discovered a new type of irregularity that populates the ionosphere just equatorward of the auroral zone every night."

The HokieDARN radar is the second mid-latitude system built in the United States and the third in the world, after the Wallops radar and a Japanese radar operated on the island of Hokkaido. It was turned on in February of this year, just in time to contribute 'ground-truth' to a major NASA satellite mission (THEMIS) that is studying the causes of the auroral substorm. The radar was built with funding from the National Science Foundation (NSF) as a collaboration between Virginia Tech, JHU/APL and Leicester University in the United Kingdom.

HokieDARN was raised by a team of scientists and engineers from the collaborating institutions lead by the new arrivals to ECE, i.e., Ruohoniemi, Baker, and Ray Greenwald, who has joined as a research professor. Greenwald pioneered the use of HF radar for ionospheric studies and is the primary founder of SuperDARN.

For more information, visit: www.space.vt.edu.