Computer Science – Sound
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11c..01a&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM11C-01
Computer Science
Sound
2403 Active Experiments, 2704 Auroral Phenomena (2407)
Scientific paper
It is with great honor that I have the opportunity to talk about some of the contributions Prof. John Winckler has made to space science and auroral physics in particular. John's interest in the aurora began on the first day of the IGY during a balloon flight designed to be the start of a campaign to do a latitudinal survey of the cosmic ray cut-off during the IGY. The detectors of this flight unexpectedly measured 50-100 keV x-rays produced by auroral electrons bombarding the top of the atmosphere. After retiring from teaching, John's interest in the dynamics of low-latitude aurora came full circle from its starting point during that first day of the IGY almost thirty years earlier. With ground photometers, cameras and stereoscopic TV, he made extensive observations of the pulsation phase of auroras during the peak of solar cycle 22. Although pulsating aurora had been studied for decades at auroral zone latitudes, John's work at sub-auroral latitudes discovered new phenomena and made observations of known phenomena in greater detail. The intent of this talk is primarily to consider Winckler's pioneering work with electron beam injections into the magnetosphere from sounding rockets. The motivation for this work initially was to map auroral field lines and to study large scale magnetospheric electric fields. The aspect of the work that I was most intimately involved in was the mechanism of neutralizing the rocket after it had injected nearly a coulomb of negative charge into space. It was initially argued that the beams would become unstable and therefore be destroyed and useless as probes of the magnetosphere. This was not the case, hence the neutralization mechanism became a significant study of the program. Although not realized at the time, it turns out that the beam injections at rocket altitude in essence became a laboratory in space in which many of the features of the aurora itself were reproduced. It is accepted that the electrons of a discrete aurora are accelerated by a potential structure one or two Re above the atmosphere. The requirement for field-aligned current demanded by the magnetic field reconfiguration in the Earth's tail during substorms is, presumably, the reason for this potential. Electrons that have interacted with this potential structure are known to contain signatures of ion cyclotron waves, perhaps a clue as to the source of the potential itself. Data will be shown from a recent rocket flight measuring both cold ionospheric electrons of field-aligned bursts and inverted V electrons originating from the tail which bear this signature. Data from the Echo rockets show very similar results. There is a need for return current to the electron-emitting payload if the beam is to escape. Ambient electrons are measured to be accelerated within a few tens of meters of the payload to carry this current. These electrons produce auroral light in collisions with residual neutral gas around the payload. Both the light and the neutralizing electrons fluctuate in intensity at heavy ion cyclotron frequencies.
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