Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsm72a..06s&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SM72A-06
Physics
2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2730 Magnetosphere: Inner, 2778 Ring Current, 7867 Wave/Particle Interactions (2483, 6984)
Scientific paper
We investigated details of an isolated proton auroral aurora observed at Athabasca, Canada (MLAT: 62, L: 4.6) at 2100-2240 MLT on 5 September 2005, using a multi-data set obtained by simultaneous ground and satellite observations. The event clearly demonstrates that a localized enhancement of 30-80 keV ions, which was observed by the NOAA 17 satellite, precipitated into an isolated proton aurora equatorward of the auroral oval. The appearance interval of the isolated proton aurora was coincident with a burst of Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The DMSP F13 satellite observed an ionospheric plasma trough, which is a signature of the footprint of the plasmapause, at the conjugate point of the isolated proton aurora in the southern hemisphere. These observations support the following scenario: EMIC waves are generated near the plasmapause in the inner magnetosphere and resonantly scatter energetic ring current ions into loss cone. The precipitating ions excite proton aurora in the ionosphere. The EMIC waves propagated into the ionosphere are detected on the ground as Pc 1 geomagnetic pulsations. Based upon multi-event analysis of one-year auroral imaging and magnetic field data at Athabasca in September 2005 - September 2006, we found that the isolated auroras were always observed simultaneously with Pc 1 geomagnetic pulsations in the frequency range of He+-band EMIC waves at the conjugate magnetic equator for all 13 events. The isolated auroras had narrow latitudinal widths (less than ~230 km) and limited longitudinal lengths (250-800 km) at an altitude of 120 km. The isolated auroras moved equatorward as associated Pc 1 frequencies increased, since the ion gyrofrequency becomes higher at smaller L values. These facts indicate that the isolated proton auroras are connected rigidly with the source region of EMIC waves by a magnetic flux tube and that the wave-particle interaction occurs in a very small region in the inner magnetosphere as indicated by the localization of the isolated auroras.
Connors Martin
Miyoshi Yasunobu
Sakaguchi Kei
Shiokawa Kazuhiko
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