With special collaboration by Trond S. Trondsen, University of Calgary Institute for Space Research
The aurora borealis represents one of the most dynamic effects of the Sun-Earth relationship. It encircles the globe's polar regions. If you are looking north at an auroral curtain just above the horizon, someone 500 kilometres east or west of you can also see it. Satellite images of the aurora have shown them to be an enduring feature of the magnetic poles.
Typically, the lower limit of an auroral curtain is about 100 km from the surface of the Earth and may be several hundred kilometres tall. The arc may extend several thousand kilometres east–west. And deep within these gigantic formations lies a microcosm—a whole new world, waiting to be discovered.
Today's better sensors, with their higher sensitivity and higher resolution, offer a wider view of the aurora. Optical imaging is a remarkably versatile tool that allows us to probe the depths of the magnetosphere. It helps us study processes which, though of the smallest scale, are directly or indirectly responsible for the generation of auroral arcs and filaments in the ionosphere. An analogy for this process is the way a hurricane develops from a dust devil.
Dr. Trondsen and others at the University of Calgary are developing a series of optical experiments that will provide the first simultaneous observations of auroral formation. He has developed a highly sensitive imaging system: the Portable Auroral Imager, to focus in on the smallest and fastest moving features in the aurora.
For decades, these features have eluded numerous ground-based, all-sky imagers and satellite imagers; this is because of the low spatial resolution (kilometres) and long exposure times (seconds) of these instruments. The Earth's magnetosphere–ionosphere system appears to be ordered when considered from afar, but upon closer inspection, it shows chaotic behaviour. Using the powerful eye of the Portable Auroral Imager, we see a scene that is constantly metamorphosing. Auroral forms that move at speeds of 100 km a second are common.
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This video filmed by the Portable Auroral Imager shows the actual speed of an the auroras.
(Video: University of Calgary)
The large quantity of data hitting the imager's lens quickly fills computer hard disks. With three terabytes (that's 3,000 gigabytes!) of raw data gathered during a two-week observation period, the imager is used only for a limited time to address specific scientific objectives. However, advanced techniques for real-time data reduction and analysis are being developed at the University of Calgary. The next-generation imager will perform routine monitoring of auroral microstructure as part of a network of imagers providing simultaneous observations of a wide range of auroral formations.
The Portable Auroral Imager affords a new and exciting perspective on the smallest of auroral features. Startling observations have been made with it: dynamic waveforms, small-scale curls, and ghostly black patches that dance across the instrument's field of view. This data is impressive—as much for its beauty as for its scientific value. The Portable Auroral Imager is one of many tools being developed, and its images are a tantalizing preview of the exciting discoveries to come.