Periodic auroral forms and geomagnetic field oscillations in the 1400 MLT region

Details Periodic auroral forms and geomagnetic field oscillations in the 1400 MLT region Periodic auroral forms and geomagnetic field oscillations in the 1400 MLT region

May 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990jgr....95.5835p&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 95, May 1, 1990, p. 5835-5844. Research supported by the U.S. Navy and NS

Physics

38

Auroras, Geomagnetism, Magnetic Disturbances, Satellite Imagery, Ultraviolet Photography, Birkeland Currents, Brightness Distribution, Electric Fields, Electron Precipitation, Magnetic Fields, Temporal Distribution, Viking Spacecraft

Scientific paper

The UV images obtained with the Viking satellite often show bright features which resemble 'beads' or 'pearls' aligned in the east-west direction between noon and 1800 MLT. Viking acquired a series of 25 UV images during a 28-min period on July 29, 1986, which showed a distinctive series of periodic bright features in this region. Magnetic field and hot plasma measurements obtained by Viking confirm that the UV emissions are colocated with the field line projection of an upward-flowing region 1 Birkeland current and precipitating energetic (about 200 eV) electrons. These observations support previous work which concludes that this region is the ionospheric projection of the cusp and low-latitude boundary layer. The magnetic field and electric field measurements show transverse oscillations (predominantly in the westward and southward components, respectively) with a nearly constant period of about 3.5 min from 67 deg invariant latitude equatorward up to the location of the large-scale Birkeland current system near 76 deg invariant latitude. The observed oscillations are interpreted as standing Alfven waves driven at a frequency near the local resonance frequency by a large-scale wave in the boundary layer. The energy flux of the precipitating low-energy electrons in this afternoon region is modulated by this boundary wave, and produces the periodic UV emission features.

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