Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsm33b..07y&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM33B-07
Physics
2400 Ionosphere (6929), 2483 Wave/Particle Interactions (7867), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934), 2704 Auroral Phenomena (2407), 2772 Plasma Waves And Instabilities (2471)
Scientific paper
In December 2002, a Versatile Electromagnetic Wave Receiver (VIEW) and a new digitization system were deployed at South Pole station to measure three types of auroral radio emissions: Auroral Roar, Auroral Hiss and Auroral medium frequency (MF) bursts. Auroral Hiss is a whistler mode wave emission with frequencies lower than 1MHz. In 2004, VIEW captured the first high resolution broad band structures of LF iss at South Pole. The data show detailed features of auroral hiss, which we classified into three different types: standard broad band auroral hiss, seen on the spectrogram as vertical straight lines several hundreds of kHz wide in frequency; patchy auroral hiss, which appears on the spectrogram as a smeared area 100-200kHz wide and several seconds long; and discrete auroral hiss, which consists of short-duration narrowband emissions appearing on the spectrogram as dark spots a few tens of kHz wide and a few tenths of a second long. A subset of this last category exhibits striation features similar to those observed in auroral roar fine structure, only at much lower frequencies (~100 KHz). We explore whether the discrete features originate from electrostatic noise peaked at local plasma frequencies excited by auroral electron beams as a consequence, for example, of convective beam amplification. The excited electrostatic noise can mode-convert to whistler mode waves some of which may propagate downward toward the ground. However, it is well known that at the bottom of the ionosphere, the k-vector of the propagating whistler wave must lie within a small cone around the vertical direction in order for the whistler wave to penetrate the boundary and continue as free space mode to reach the ground. We combine a ray-tracing code with a model auroral ionosphere to explore accessibility to the ground of waves generated by convective beam instability near the plasma frequency at different altitudes. The studies will help distinguish whether the discrete features can result from wave propagation effects, or whether they must result from the source mechanism.
LaBelle James
Ye Shuzhen
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