For the past 15 years, engineers and scientists have gained a greater understanding of global warming, the effects of geomagnetic storms, the impact of the solar wind interacting on the magnetized region around the earth, and other dynamic processes that occur in the Earth's near-space environment.
Among their tools, they use a high-latitude network of radars to obtain increasingly sophisticated views of electric fields, plasma structures, atmospheric waves, and other effects in the ionosphere and atmosphere.
The radars have an elaborate technical name –– the Super Dual Auroral Radar Network –– providing an acronym with a humorous touch, SuperDARN. The network is an international collaboration with support provided by the funding agencies of more than a dozen countries. The radars combine to give extensive views of the upper atmosphere in both the Arctic and Antarctic regions.
The view is about to get much bigger.
Virginia Tech’s J. Michael Ruohoniemi, associate professor of electrical and computer engineering in Virginia Tech’s College of Engineering, is the lead principal investigator on a new $6 million grant to build additional radar units. Nearly $2 million of the award will go to Virginia Tech and Ruohoniemi’s research center, Space@VT, directed by Wayne Scales, also of electrical and computer engineering.
Other participants in the grant from the National Science Foundation (NSF) are Dartmouth College, University of Alaska at Fairbanks, and the Johns Hopkins University Applied Physics Laboratory (JHU/APL). The Virginia Tech group is directing the first construction that will take place at a site in Kansas later this year. Other potential sites are currently being reviewed in Oregon, the Aleutian Islands, and the Azores.
Ruohoniemi, formerly of JHU/APL and involved with SuperDARN since his days as a junior scientist, was instrumental in the move of APL’s highly prestigious SuperDARN Radar Group to Virginia Tech in 2008. The enticement of the Blacksburg campus was due to several key factors including Scales’ build-up of Space@VT and Virginia Tech’s ability to attract students and award Ph.D.s in the engineering disciplines.
“We wanted to increase the exposure of U.S.-based students to SuperDARN and to radar techniques for space research and engineering,” Ruohoniemi said.
Construction of the new radars will occur in pairs at a rate one pair per year at each of four sites, for a total of eight radars over four years. The new radars will join three existing mid-latitude radars to make up a continuous chain of coverage that extends from Europe to eastern Asia.
As Ruohoniemi explained the science, “The Earth’s magnetosphere is immersed in the tenuous, fully-ionized outer atmosphere of the sun, which is responsible for the solar wind and its structured and dynamic magnetic field. In the aftermath of severe solar disturbances, such as solar flares, energized solar wind plasma impinges on the Earth’s magnetic and plasma environment and initiates a broad range of interactions. These reactions lead to the onset of disturbances in the magnetosphere.
“During these events, the magnetosphere-ionosphere system passes through a range of states that can be described as quiescent, mildly disturbed, and storm-like. As each transition takes place, the effects of disturbance reach to ever increasing fractions of the Earth’s plasma environment. The consequences of these solar-induced disturbances are often described as space weather and they can threaten harm to humans in space, perturb spacecraft orbits, damage spacecraft electronics, and disrupt radio, radar, and GPS operations.”
SuperDARN is the sole instrument that is capable of providing direct measurements of plasma convection and electric fields in the ionosphere on global scales with high temporal resolution.
Virginia Tech has operated a midlatitude radar at the University’s Blackstone Agricultural Research and Extension Center since February 2008. Ruohoniemi and Joseph Baker, also of Virginia Tech’s ECE department and formerly of JHU/APL, are responsible for its daily operation and share in the responsibility for the operation of a radar at the NASA Wallops Flight Facility located at Wallops Island. Ray Greenwald, described by Scales as the “godfather” of the SuperDARN group, is now retired from JHU/APL, but continues to work as a research professor with Space@VT. The VT SuperDARN group also manages two older SuperDARN radars located at auroral sites in Labrador and northern Ontario.
The first SuperDARN-type radar was the one constructed in Labrador in 1983 by JHU/APL. The second radar was constructed at Halley Station, Antarctica, in 1987 in partnership with the British Antarctic Survey. Together, these two instruments produced the first simultaneous, conjugate images of the pattern of ionospheric plasma flow responding directly to changes in the orientation of the magnetic field carried by the solar wind plasma, a result published by Greenwald and colleagues in 1991.
The success of the first pair of radars led to the formulation of the SuperDARN concept in 1992 when an international team of space scientists, led by Greenwald, conceived of a global-scale network of coherent scatter radars at high latitudes in both hemispheres with overlapped fields-of-view. The original plan included eight radars in the northern hemisphere and four radars in Antarctica but has since expanded to include the 22 radars in operation today. SuperDARN is managed as a collaborative effort with the partners agreeing to common scheduling, software, and data distribution protocols and is often cited as a prime example of international cooperation in research.
In the late 1990s, Ruohoniemi and JHU/APL colleague Kile Baker developed a technique widely used by the space science community. It allows scientists to combine all available data in a given hemisphere to map the large-scale pattern of ionospheric plasma circulation. The product is analogous to weather maps in the troposphere but with ‘plasma winds’ that are associated with variation in electrical (rather than barometric) pressure.
The new radars are aimed at adding a mid-latitude component to SuperDARN. “We realized that the convection pattern sometimes expands beyond the 60 degree limit of the high altitude radars, especially during storms,” Ruohoniemi said. In 2005, he was among the JHU/APL researchers who established the prototype of a midlatitude SuperDARN radar at Wallops Island, Va. “Observations from this facility indicated that SuperDARN radars sited at mid-latitudes were capable of making useful measurements at almost all levels of geomagnetic activity,” he added.
The success of the Wallops radar prompted construction of two additional midlatitude SuperDARN radars, one deployed in 2006 in Hokkaido, Japan, by Japanese scientists and the second deployed in 2008 at Blackstone. Scientists and engineers from Virginia Tech, JHU/APL, and the University of Leicester of the United Kingdom cooperated in the build of the Blackstone facility.
NSF funded this project specifically to provide the community with new research infrastructure. With its completion in 2012, Joseph Baker said three broad areas of research will be addressed: plasma convection in the inner magnetosphere-ionosphere system, plasma structuring and sounding, and upper atmospheric phenomena such as winds and waves. One aspect of this research would center on the specific cause of auroral substorms, the most widely studied phenomena of space physics, yet remaining the “most controversial,” Baker said.
With the new midlatitude infrastructure, researchers will be able to observe substorm processes at lower latitudes than is currently possible. They will also be able to merge overlapping measurements from pairs of radars to map the structure within substorm flows at high spatial and temporal resolutions.
During geomagnetic disturbances, the space weather effects include enhanced gradients in ionospheric plasma density and the occurrence of irregular plasma structure. These can lead to anomalies in the performance of GPS systems, according to electrical and computer engineering assistant professor Brent Ledvina, also a member of Space@VT.
“It should be noted that there will be a particular concentration of SuperDARN radars in the North American sector. We will be able to continuously track the ionospheric impacts of disturbance in Earth’s space environment as they expand from high polar latitudes through the auroral zone to the heavily populated and technologically sensitive areas of southern Canada and the United States. The completion of this project will be a very significant milestone in the development of a space weather radar system.” Ruohoniemi summarized.