Sunday, September 6, 2009

Magnificent Auroras


One of the science destinations near the top of my list is to visit a northern (or southern for that matter) latitude to witness an aurora. Witnessing the so-called Northern or Southern Lights seems like a wonderful way to visualize a scientific process in action as well as take a pretty exotic trip.

Auroras are caused when charged particles (mostly electrons, but also protons and other heavier particles) from space collide with gas particles in the upper atmosphere (ionosphere, at altitudes above 80km). The phenomena are typical at higher latitudes because the particles follow the Earth’s magnetic field lines (see attached graphic). Notice how the field lines penetrate the atmosphere at the polar regions. The magnetosphere of Earth is a region in space whose shape is determined by the extent of Earth's magnetic field.

Scientists have always thought the north and south auroras mirror one another because magnetic field lines connect the two hemispheres. A new report by researchers in Norway (July 23 Nature) finds that the intensity and pattern of the northern and southern auroras can differ substantially. The differences were imaged by simultaneous satellite observations. Known differences in Earth’s magnetic field strength don’t explain the new data. There are some theories about the auroral asymmetries; they may be driven by large numbers of charged particles flowing between the northern and southern hemispheres along magnetic field lines.

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