Project porcupine : the MF mutual-impedance probe experiment. Part II : Flight F3 and F4 (March 1979)

Résumé : This is the second part of a report on the results from the medium-frequency (MF) mutual-impedance probe experiment that was supplied by the Centre for Research in Environmental Physics (CRPE, Orléans, France) as a contribution to the West-German Porcupine program of research on auroral physics during the International Magnetospheric Study. The subject of Part 1 was the results from the first successful flight, named F2, which took place from ESRANGE (Kiruna, Sweden) on 20 March 1977. On that occasion, the MF probe experiment did not succeed in its objective of detecting field-aligned drift motion of the thermal electrons in the auroral ionosphere. The non-reciprocal shift of the lower oblique resonance (L.O.R.) frequency that this motion should have produced was masked by a similar but much larger shift that was obviously spurious, since it varied, more or less sinusoidally, as a function of the spin-phase angle. Various conceivable physical causes for this spurious shift were studied, but were rejected. The question of whether the true cause was some other physical phenomenon, as yet unidentified, or whether it was technological in nature, had to be left open. The results from the flight F2 nevertheless suggested a number of ways in which the experiment could be improved, and these were discussed in Section 5, which concluded Part 1 of the report. In Part 2, after the present preface, Section 7 describes how these and other modifications were made to the MF probe, in preparation for the flights F3 and F4. The changes that were made to some of the other instruments on board are mentioned also. The flight F3 took place on the evening of 19 March 1979, during a quiet interval within a period of repeated auroral activity. A weak negative magnetic bay of about 100 y (K = 2 ) was in progress at the time of launch : see § 7.2. of the report by Haüsler et al. [1982] . The aurora failed to evolve as anticipated, and the payload did not pass through any discrete arc. These relatively calm conditions, which disappointed the other experimenters, were ideal for determining whether the various modifications had improved the MF probe. In Section 8, where the results of the F3 experiment are presented, emphasis is therefore laid on analysis of the technical performance of the probe. The flight F4, on the evening of 31 March 1979, took place during a strong magnetic substorm ( p = 5+). At the time of launch, a discrete visual arc was present with a sharp northern edge, and the trajectory of the payload crossed this edge ; see § 7.3. of the report by Haüsler et al. [1982] . Stronger electric fields were encountered on this flight than on F3, and much of our study of the experimental results in Section 9 has been devoted to clarifying certain effects that appear to have been caused by these fields, and which resemble the spurious effects already observed on F2 inasmuch as they depended on spin phase and masked the interesting effects that we were looking for. The conclusions, presented in Section 10, are drawn from the results of all three successful flights. They substantiate the progress made in the development of the MF mutual-impedance probe as a means for measuring the field-aligned drift velocity of the thermal electrons, and indicate how, by further development, it might be made into a reliable instrument for this purpose.
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L.R.O. Storey, J. Thiel, J.M. Illiano. Project porcupine : the MF mutual-impedance probe experiment. Part II : Flight F3 and F4 (March 1979). [Rapport de recherche] Centre de recherches en physique de l'environnement terrestre et planétaire (CRPE). 1981, 194 p., figures, graphiques. ⟨hal-02191501⟩

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