Remote Sensing of the Auroral Magnetosphere From the Ground Observations of Impulsive Auroral Hiss

Details Remote Sensing of the Auroral Magnetosphere From the Ground Observations of Impulsive Auroral Hiss Remote Sensing of the Auroral Magnetosphere From the Ground Observations of Impulsive Auroral Hiss

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11a0768h&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM11A-0768

Physics

2407 Auroral Ionosphere (2704), 2439 Ionospheric Irregularities, 2471 Plasma Waves And Instabilities, 2487 Wave Propagation (6934), 2772 Plasma Waves And Instabilities

Scientific paper

We propose a new remote sensing method to determine auroral region cold plasma densities from the ground observations of impulsive auroral hiss (IAH). This method is based on a new model of IAH propagation to ground. In this model, IAH is generated at large wave normal angles along auroral field lines by ~ 1-10 keV electrons via Cerenkov mechanism. IAH propagates from the source region to the ground along field aligned density cavities and enhancements (ducted mode) up to ≈ 3000-5000 km altitude and then scatters from meter-scale irregularities to the ground. Using this new understanding of IAH propagation to the ground, we propose a method to determine the AH source region, energetic electron parallel resonance energy, and cold plasma electron concentrations along auroral field lines. We begin with tentative density models of the auroral magnetosphere that match with past experimental and theoretical work. We then perform raytracing calculations to match the observed dispersion with the dispersion calculated from our raytracing simulations. In general, this match requires that IAH source altitude is a function of frequency as well as cold plasma density, thus giving us a method to determine both the source location and the cold plasma density. The initial wave normal at the source location along with local cold plasma density (determined from the dispersion) and local gyrofrequency (from a model), leads to calculation of electron parallel energy required to generate the hiss via Cerenkov mechanism. To explain our technique, we analyzed an IAH spectra recorded at South Pole, Antarctica, on July 09, 1996 0005 UT to show that, for the sample spectrogram, the AH source region for frequencies 7-9 kHz should be >16,000 km while for frequencies 12-20 kHz it should be <8000 km. We also show that the parallel resonance energy of the energetic electrons generating the frequencies should be <1 keV, and the cold plasma electron concentration along the field line Λ =79o showing a R-5 dependence outside the plasmasphere should be ~ 100 el cm-3 at 12,740 km altitude.

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