Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm51d..08l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM51D-08
Physics
Plasma Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [6939] Radio Science / Magnetospheric Physics, [7847] Space Plasma Physics / Radiation Processes
Scientific paper
The Earth's auroral electrons radiate away up to ~1% of their energy in the form of radio waves, called Auroral Kilometric Radiation (AKR), making the Earth a powerful radio emitter. The mechanism responsible for the radio emission, called the electron cyclotron maser (ECM), produces similar emissions at the other magnetized planets, in the solar atmosphere, and possibly in astrophysical systems such as pulsars and blazars. AKR was not unambiguously identified until the 1970's because its detection requires a suitably instrumented satellite. The ECM theory applied to AKR predicts radiation beamed outward that cannot penetrate the increasing magnetic field and electron density near the Earth. Nevertheless, there have been curious observations over the years of AKR-like radio signals detected by ground-based, rocket-borne, and low-earth orbiting satellite-borne instruments, raising the question of whether mechanisms exist by which AKR can penetrate to low altitudes. Here we show the first unambiguous evidence that AKR does indeed penetrate to low altitudes on occasions. For three examples of AKR-like emissions detected at ground level at South Pole Station, Antarctica, we examined data from the Geotail satellite plasma wave receiver, which had a field of view that included the auroral field lines above the station. The AKR-like emissions detected at ground-level have the same frequency-time structure as simultaneous AKR emissions detected on Geotail 115,000-190,000 km away from the Earth. Slight differences in the frequency extent of the emissions at the two locations can be explained by, for example, plasmaspheric screening of the emissions detected by Geotail. These observations represent the first reported coincident detections of AKR in space and on the ground. They require a mechanism to produce the ground-level emissions, they suggest that previous AKR-like emissions observed at low altitudes may indeed be AKR, and they require revision of the widely-held textbook view that AKR is only detectable from space.
Anderson Rachel
Labelle James W.
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