Rocket Measurements of Auroral-Zone Energetic Electrons at Syowa Station, Antarctica. II. Characteristics of Electrons under Active Auroral Conditions

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Some fundamental properties of auroral electrons with energies greater than 40keV were measured by a series of seven sounding rockets launched from Syowa Station, Antarctica, during the IMS period of 1976-78. The payload consists of a set of proportional counter and plastic scintillation counter covering several fixed energy bands. Measurements under different conditions of active aurora were carried out four times in the altitude range of 70 to 220km. The observation results are discussed in comparison with those given by the other three quiet-time measurements, in terms of altitude profile, pitch angle distribution and energy spectrum. Principal characters of behavior of energetic electrons based on the comparative studies are summarized as follows : a) A peak in the intensity-altitude profile appears around 120km in altitude at disturbed time, counting rates being 5×(10)^5/(cm)^2・s・sr・keV for 40keV electrons in maximum, while the profile at quiet time is saturated at a counting rate of (10)^3/(cm)^2・s・sr・keV. b) Pitch angle distribution changes from the field-trapped mode in quiet condition into the fieldaligned one at disturbed time. c) The value of power law exponent of energy spectrum is found to be 7-8 at disturbed time, while about 4 at quiet time.
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