Understanding of Northern lights deepens

Author:  Getz Matthew
Date:  August 2008

For years the phenomenon of the aurora borealis, or the Northern Lights, has amazed spectators. Yet, the cause for these spectacular auroral displays has puzzled scientists until a recent breakthrough. A new study, published in the July 25th edition of Science explains how the brightening is generated in outer space, which then causes the observable polar flare-ups.

In the study, Vassilis Angelopoulos, of the University of California, Los Angeles, and his colleagues report that when the lines of the Earth's magnetic field reconnect, a large amount of energy spreads through the Earth's outer atmosphere. This results in a jet of charged particles that is projected toward Earth to light up the polar auroras. "The findings change our understanding of how the auroras are generated," says Angelopoulos.

Previously, scientists knew that it was the interaction of the sun's and Earth's magnetic fields that caused the auroras, but they were unaware how the energy that causes them was released. The study suggests that it is through substorms, which are sudden, violent eruptions in the space environment outside Earth's atmosphere, that the energy is emitted.

For the first time, Angelopoulos and his colleagues were able to watch how and where in space the substorms originated by using five satellites and a ground-based observing network in Alaska and Canada that are part of NASA's Time History of Events and Macroscale Interactions During Substorms, or THEMIS.

Substorms occur when solar energy is stored for several hours in the Earth's magnetotail, which is the long wind-sock shaped extension of the Earth's magnetosphere on the side facing away from the sun. The magnetosphere is a region of space surrounding Earth where phenomena are controlled by the planet's magnetic field. The energy is released when the Earth's magnetic field lines above and below the magnetic equator reconnect within the magnetotail. Using the satellites and THEMIS, the researchers discovered that it was this reconnection that resulted in the conversion of the stored magnetic energy into kinetic energy and heat in the Earth's atmosphere. Their findings suggest that it is this reconnection and conversion of energy that is the first event in a series leading to the polar auroras.

Charged particles, which are the result of this conversion, then accelerate down the magnetosphere toward Earth where they collide with the atmosphere and spark the aurora flares and glow. The team was able to observe this sequence of events, which takes a bit under two minutes. "This is the first time that we are able to nail' the time sequence of the events during a substorm and identify the trigger," Angelopoulos says. He and other scientists believe that this research can be used to better understand and predict space weather, which can adversely affect satellite communications and threaten astronaut safety.

Written by Matthew Getz

Reviewed by Maria Huang

Published by Pooja Ghatalia.