HR: 1330h
AN: SM43C-07    [Abstracts]
TI: High Resolution Measurement of LF Auroral Hiss at South Pole
AU: * Ye, S
EM: Shengyi.Ye@dartmouth.edu
AF: Dartmouth College, Department of Physics and Astronomy, Hanover, NH 03755 United States
AU: LaBelle, J
EM: jlabelle@aristotle.dartmouth.edu
AF: Dartmouth College, Department of Physics and Astronomy, Hanover, NH 03755 United States
AB: In December 2002, a Versatile Electromagnetic Wave Receiver (VIEW) and a new digitization system were deployed at South Pole station(-74° magnetic latitude). The motivation was to measure three types of auroral radio emissions: Auroral Roar, a relatively narrowband (δf/f<0.1) emission near 2 and 3 times the F region ionospheric electron cyclotron frequency (f_ce); Auroral Hiss, a whistler mode wave emission with frequencies lower than 1MHz; and Auroral medium frequency (MF) burst, broadband impulsive radio emissions observed at ground level during the breakup phase of auroral substorms. High resolution broad band structure of those three emissions are recorded automatically at South Pole, and are crucial to our understanding the mechanism and relations of auroral radio emissions. This experiment uses a 3×3 meter square magnetic dipole antenna, located 1.7 km away from the South Pole station. A pre-amplifier is buried right below the eastern pylon of the antenna, connected by a 1.7 km long co-axial cable to a LF-HF receiver in the station. The output of the receiver is fed into the Versatile Electromagnetic Wave Receiver (VIEW) and Windows system equipped with a digitization board. Customed software was used to digitize the selected signals at 1-2 MHz. This data acquisition system was designed so that researchers at Dartmouth College can review the data from South Pole weekly and save interesting parts according to instructions sent from Dartmouth. In the year of 2004(from Jan through September), the experiment concentrated on the auroral hiss frequency band, covering either 0-500 kHz or 0-1000 kHz. With 3-6 hours window per day, VIEW captured more than 30 GBytes data of auroral hiss waveforms. Many experiments report wave forms of VLF auroral hiss at f < 30 kHz. We focused on waveforms of LF auroral hiss, typically at 100-300 kHz. At these frequencies, the hiss shows striking fine structure. We classified our LF hiss events into three different types: standard wide band feature, seen on the spectrogram as vertical straight lines several hundreds of kHz wide in frequency; patchy feature, which apprears on the spectrogram as a smeared area a couple of hundreds kHz wide and several seconds long; and discrete features, small sparse regions of emission, shown as dark spots of a few tens of kHz wide and a few tenths of a seconds long on spectrograms. We also find some cases showing that the intensity of LF auroral hiss is modulated by a frequency in the ~30 Hz range; in other words, the hiss is flickering. Auroral hiss has sometimes been considered a featureless impulsive emission; however, VLF observations have long shown structure in auroral hiss, such as hisslers for example, and our observations show that LF hiss is likewise characterized by complex structure.
DE: 0689 Wave propagation (4275)
DE: 2407 Auroral ionosphere (2704)
DE: 2471 Plasma waves and instabilities
DE: 2487 Wave propagation (6934)
DE: 2704 Auroral phenomena (2407)
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly