The Earth is surrounded by a dynamic space plasma environment called the magnetosphere which is controlled by activity on the Sun, such as solar flares. In turn, disturbances in the magnetosphere are transmitted along magnetic field lines to the electrically charged upper atmosphere (the ionosphere). The aurora is but one example of an upper atmosphere space weather phenomenon that has its ultimate origins on the Sun. Because the Earth's magnetic field has a symmetric shape (similar to that of a bar magnet) space weather perturbations should be largely symmetric across the magnetic equator: both hemispheres should basically behave similarly. But this might not always be true.
ECE's Joseph Baker has received an NSF CAREER award to study north-south asymmetries in the Earth's ionosphere with the Super Dual Auroral Radar Network (SuperDARN) and very low frequency (VLF) receivers. Baker, along with Mike Ruohoniemi and Ray Greenwald, runs the Virginia Tech SuperDARN laboratory (see sidebar).
"Under most circumstances, space weather disturbances at middle to high latitudes in the two hemispheres should look very similar, despite the fact that local ionospheric conditions might be very different," says Baker. "For example, a large burst of upper atmosphere wind in the Southern Hemisphere should produce an ionospheric disturbance that drives a current to flow along magnetic field lines from the Southern Hemisphere into the Northern Hemisphere at least in theory," he explains. Basically, a wind burst at one end of a magnetic field line produces a noticeable ionospheric effect at the other end. "The extent to which this actually happens is still an open question." According to Baker, "there is a lot to this dynamic that we don't yet fully understand."
Ionospheric space weather convection patterns for the Northern Hemisphere (top) and Southern Hemisphere (bottom). According to Baker, "there are symmetries and antisymmetries in the patterns that speak to inter-hemispheric space weather connections."
Baker's goal is to identify different kinds of transient features in the SuperDARN radar data at middle to high latitudes and map them between the hemispheres using magnetic field models. If a radar system in the Southern Hemisphere sees a particular feature that was not seen by northern radars looking at the same magnetic field lines, "then there's either something wrong with the accuracy of the magnetic field model or our understanding of the extent to which the dynamics between the hemispheres should be linked together by magnetic field lines."
Baker is excited about the potential for student involvement at all levels of study. "The idea of magnetic connectivity is fairly easy to explain to an educational audience at all levels," he says. Baker has plans for pre-college students, for undergraduate students, and for his graduate researchers.
In conjunction with Virginia Tech's Center for the Enhancement of Engineering Diversity (CEED) summer camps, Baker plans to explain basic magnetism concepts to middle and high school students and send them out with very low frequency (VLF) receivers to listen for "whistlers." Whistlers are electromagnetic waves produced by lightning that then travel along magnetic field lines to the other hemisphere where they can be heard using a VLF receiver, antenna, and headphones. The sound is a musical descending tone that lasts for a second or more, depending on the distance traveled. Whistlers were first identified by radio operators during the First World War, and their origin remained a mystery for some time.
Baker would like to see his undergraduates doing the same thing, but with more understanding and analysis. Whistlers are still an active area of research to this day, he explains. "You can use the frequency characteristics of whistlers to remotely sense conditions in the magnetosphere: you can figure out what the plasma density is further out in space."
A team of students from Baker's "Exploration of the Space Environment" class launched a high altitude balloon to take pictures and measurements of the upper atmosphere.
Baker teaches a new class on introductory space science called Exploration of the Space Environment, which is available to students in all majors. For this class, Baker currently offers several options for a semester project, and would like to add another option that involves analyzing whistlers. Students choosing this project option would build a VLF receiver from a kit, listen for whistlers, analyze the data, and use information from worldwide weather services to locate any lightning storms occurring in the Southern Hemisphere at the time of the whistlers they identify.
Baker also plans for some of his graduate and advanced undergraduate students to use a more powerful receiver designed by colleagues at Stanford University that operates in the extremely low frequency (ELF) and VLF range. Baker describes this receiver, called the Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education (AWESOME) monitor, as "a research-grade ELF/VLF receiver."
This monitor, Baker says, "will allow Virginia Tech undergraduate students to grasp the diversity of natural phenomena that can be studied using radio instrumentation: lightning physics, lightning-ionosphere interaction, solar flares, gamma-ray bursts, earthquake-ionosphere coupling, auroral electron precipitation, magnetospheric physics." He would like some undergraduate researchers to become a regular part of his research team's efforts.