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Auroral Turbulence II (A.T. II)
Launch date: 11 February, 1997
Launch time: 8:36 UT
Launch team: Principal Investigator: Torbert, Rau, Lynch, Pietrowski (UNH); LaBelle, McAdams, Trimpi (Dartmouth); Kelley (Cornell); Danish Meteorological Institute
Vehicle apogee: 545.9km after 428 seconds of flight
Location: Poker Flat, AK (65.13¡ N, 147.48¡ W)
Instrument list: Three diagnostic payloads that carried identical basic plasma instruments. Ion and electron spectrometers (UNH), Electric Field Instruments (Cornell, Dartmouth, UNH), Magnetometers (Technical University at Denmark).Ê In addition, the main payload carried: wave-particle correlator (UNH), Plasma Frequency Probe, Wideband HF Wave Receiver (Dartmouth), and , Faraday Ring Ammeter (UNH/Danish Meteorological Institute)
Dartmouth provided a 0.4-5.0 MHz wideband receiver to the auroral turbulence II sounding rocket, launched to over 500 km into active aurora.
The antenna used for this receiver was a 5-m Weitzmann antenna oriented perpendicular to the payload which was aligned with the magnetic field. Hence, the antenna favorably picks up modes with electric field perpendicular to the magnetic field, although parallel polarized waves are also detected since the rocket alignment was not perfect.
The receiver detected two bands of emissions. The frequency of each band, apparently related to electron density, decreased with increasing altitude. This leads to minimum frequency detected at apogee, and the two bands appear on a spectrogram as two parallel "necklaces." A similar "necklace" shape has been detected on some other rocket experiments.
The upper band is probably associated with the upper hybrid frequency. The lower band has an upper cutoff near the plasma frequency and probably consists of whistler waves and occasionally Langmuir waves.
The antenna orientation seems to play a significant role in determining which wave modes are detected, since the Phaze-II receiver, flown into active aurora one day earlier but with a parallel antenna rather than perpendicular, detected only one band near the plasma frequency rather than two bands as measured with the Auroral Turbulence II system. A comparative analysis of several flights with different antenna configurations is underway.
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McAdams, K. L., Sounding Rocket Based Investigations of HF Waves in the Auroral Ionosphere, Ph.D. Thesis, Dartmouth College, Hanover, N.H., 1999.