May 31, 2009 Chorus waves, a type of electromagnetic emission generated by electrons in Earth's radiation belt, play an important role in both accelerating and removing the energetic radiation belt electrons that can disrupt satellite electronics and disturb communications with ground-based operators.
To improve understanding of the origin and location of chorus waves, a team of researchers used data from NASA's five Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites to create a new map of their distribution. They reported their findings in a recent issue of Geophysical Research Letters.
The authors (Li et al.) found, in agreement with previous studies, that nightside chorus occurs only near the equator, whereas dayside chorus extends to higher latitudes.
In addition, they observed that amplitudes of chorus waves depend strongly on geomagnetic activity. The most important new finding, the authors note, is that at a distance of more than 7 Earth radii (about 45,000 kilometers) on Earth's dayside, moderate chorus is present more than 10 percent of the time (a much higher occurrence rate than on the nightside) and persists even during periods of low geomagnetic activity. The authors believe that the new information could provide additional clues about the origin of dayside and nightside chorus waves.
The team included scientists from the University of California, Los Angeles, the Swedish Institute of Space Physics, the Centre d'étude des Environnements Terrestre et Planétaires in France, Technischen Universität Braunschweig in Germany, and the Austrian Academy of Sciences.
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- Li, W., R. M. Thorne, V. Angelopoulos, J. Bortnik, C. M. Cully, B. Ni, O. LeContel, A. Roux, U. Auster, and W. Magnes. Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft. Geophysical Research Letters, 2009; 36 (9): L09104 DOI: 10.1029/2009GL037595
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