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Boundary Between Earth’s Magnetic Field and Sun’s Solar Wind Riddled with "Swiss Cheese" Holes

21.03.2003

Aurora Australis--the Southern Lights--over the geodesic dome at the National Science Foundation’s Amundsen-Scott South Pole Station. The aluminum dome has housed the main station buildings since the 1970s. The Amundsen-Scott station is one of three United States research stations on Antarctica. The National Science Foundation operates them all.

The Aurora Australis is the atmospheric phenomenon known familiarly as the Southern Lights. Like its more familiar counterpart, the Aurora Borealis--or Northern Lights, the phenomenon is caused by the solar wind passing through the upper atmosphere. But the Aurora Australis is far less frequently observed because so few people live in Antarctica during the austral winter.
Photo Credit: Jonathan Berry, National Science Foundation

Magnetic fields explosively release energy in events throughout the universe, from experiments conducted in laboratories to huge outbursts within galaxies. On the Sun, these magnetic explosions are responsible for solar flares and ejections of material from the Sun’s corona.

Similar events associated with Earth’s magnetic field drive magnetic storms, and the dramatic brightening and expansion of the northern and southern lights, the aurora borealis and aurora australis. The reconnection of twisted and complex lines of magnetic force relates these phenomena to each other.

Scientists have long debated whether the fast release of energy that occurs during "magnetic reconnection" is a smooth or turbulent process. Scientists funded by NSF have now used large-scale computer simulations, combined with direct observations from satellites, to show that the energy release is likely the result of turbulent processes.

This knowledge may explain the effect of solar storms on Earth, from interruptions of satellite orbits to electrical outages in cities and towns.

According to recent research results by James Drake at the University of Maryland in College Park and other scientists, the intense electric currents generated during magnetic reconnection produce "electron holes," regions where electrons are sparse.

Satellite observations have shown that the boundary between Earth’s magnetic field and the solar wind (known as the magnetopause) is riddled like Swiss cheese, with holes that may reach several miles in diameter. The holes move in the opposite direction of the prevailing electric current at speeds that can be faster than 1,000 miles per second, or 4 million miles per hour.

Says Kile Baker, program director in NSF’s division of atmospheric sciences, which funded the research, "The birth and death of these electron ’holes,’ and the intense electric fields associated with them, lead to strong electron scattering and energizing."

An understanding of this process is critical to explaining why magnetic explosions in space release energy so quickly, and so explosively, he adds.