Predicting geomagnetic storms

Eruptions from the sun’s outer atmosphere can hurl million-ton clouds of electrically charged ions toward Earth. Moreover, solar flares spew high-energy X rays and high-speed charged particles. Recent observations with an Earth-orbiting spacecraft may yield new ways to predict when these solar temper tantrums will cause the geomagnetic storms that disrupt communications systems on Earth and harm satellites.

Using a satellite called IMAGE (Imager for Magnetopause-to-Aurora Global Exploration), researchers for the first time obtained images of the sun pumping material into its plasma sheet, which is made of highly ionized atoms and pierces Earth’s magnetic field. The scientists also confirmed that when the magnetic field carried by the plasma sheet points opposite to the direction of Earth’s magnetic field, material within the sheet can penetrate Earth’s protective magnetic bubble.

Only if the plasma sheet is full and it has an oppositely pointing magnetic field can a geomagnetic storm be triggered, according to the 20-day study with IMAGE.

Previous measurements of the plasma sheet and the magnetic field it carries were confined to small regions that couldn’t readily be stitched together into a global picture of the forces involved in triggering geomagnetic storms, says David J.

McComas of the Southwest Research Institute in San Antonio, Tex.

McComas and his colleagues describe their study in the Nov. 15, 2002 Geophysical Research Letters, mailed this month.


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