HR: 0800h
AN: SM41B-1187    [Abstracts]
TI: HF "Swishers" Observed with a Recent Sounding Rocket: A Ray Tracing Study
AU: * Colpitts, C A
EM: cac@dartmouth.edu
AF: Dartmouth College, Department of Physics and Astronomy, Hanover, NH 03755 United States
AU: Yoon, P
EM: yoonp@glue.umd.edu
AF: University of Maryland, Institute for Physical Science and Technology, College Park, MD 20742 United States
AU: Samara, M
EM: marilia@aristotle.dartmouth.edu
AF: Southwest Research Institute, 6220 Culebra Road, P.O. Drawer 28510, San Antonio, TX 78228 United States
AB: The sounding rocket SIERRA (Sounding of the Ion Energization Region: Resolving Ambiguities) was launched duing a rocket campaign at the Poker Flat, Alaska, rocket range (65.13° W) on January 14, 2002. It reached an apogee of 735 km at approximately 500 s into the flight. A high frequency electric field instrument (HFE) provided by Dartmouth College was included in the payload. The HFE continuously measured the full electric field waveform up to 5 MHz and transmitted it to the ground via a wide band analog telemetry. Among the wavesforms detected by the HFE was a new signature that we term "swishers," time-dispersed signals at 1.2 to 1.6 MHz in which the higher frequencies were observed first and the lower frequencies observed delayed by tens of milliseconds. Several dozen of these waveforms were detected during a 20 second span on the upleg of the flight, when the rocket was in an underdense region (fpe<fce). We put forth that the swishers may start out as an impulse, with all frequencies generated at one time and place, and obtain their observed dispersion because the lower frequencies are approaching a cutoff frequency, one below which waves of this particular mode cannot propagate. As the frequency of a plasma wave approaches one of these cutoffs, its group velocity goes to zero, so packets of waves with a frequency close to this cutoff would travel more slowly and thus arrive at the rocket at a later time. Assuming that the emissions start out as an impulse, this model would result in dispersion qualitatively much like that observed in the SIERRA data. Ray tracing calculations will be done to test this hypothesis and attempt to constrain the modes of the waves and determine the size, location, and motion of their sources.
DE: 2407 Auroral ionosphere (2704)
DE: 2467 Plasma temperature and density
DE: 2471 Plasma waves and instabilities (2772)
DE: 2483 Wave/particle interactions (7867)
DE: 2487 Wave propagation (0689, 3285, 4275, 4455, 6934)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005