Imager Eases Analysis of Space Weather

Michael J. Lander

There’s more to bad weather than just wind and rain. When flares or coronal mass ejections occur on the surface of the sun, ensuing blasts of radiation cause storms in the Earth’s ionosphere, more than 100 km above land and sea. In fact, storms occur near the planet’s magnetic equator even under a quiet sun. Although these blustery conditions take place beyond our view, they can disrupt satellite communication, disable power grids and dramatically affect other human activities.

An airglow imager and other instruments at Cerro Tololo Inter-American Observatory in Chile imaged ionospheric disturbances, which, unlike auroras, are invisible to the unaided eye. They are seen here as dark vertical bands. The largest one, near the center of the photo, lay 500 km above the Earth and was about 70 km wide.

Researchers led by Jonathan J. Makela of the University of Illinois at Urbana-Champaign have used a narrow-field ionospheric airglow imager and two global positioning system scintillation monitors at the Cerro Tololo Inter-American Observatory near La Serena, Chile, to get a better picture of what causes these events.

The imager, which the scientists installed last year, takes advantage of a phenomenon called airglow to visualize space weather. After radiation from the sun ionizes gas molecules during the day, the released electrons recombine at night, causing the emission of photons.

Where severe perturbations of the ionosphere occur, the glow caused by this and other molecular events appears diminished -- depletions that the imager reveals with narrow-band filters and exposure times of one to two minutes. These same turbulent zones cause radio waves to scintillate — the root of much disruption to satellite signals. The global positioning system monitors enabled the researchers to perform interferometric calculations as well as to examine drift velocities and other smaller features.

The scientists presented early results of their ongoing research at the American Geophysical Union meeting in December. Already, their images and calculations have helped them develop new ways to study the time, location and severity of the disturbances.

When they compare the information with radar backscatter observations from the Jicamarca radar system near Lima, Peru, and with similar data gathered in Colombia and other locations, they may discover interactions that contribute to global trends in ionospheric activity. Combined with existing knowledge, these insights could enable navigation and communication systems that can better withstand these faraway storms. Visit http://airglow.csl.uiuc.edu/facilities/CTIO/PICASSO.avi to see a movie filmed at the site.