Abstract
Abstract. The pitch-angle distributions (PAD) of energetic particles are examined as the ISEE-1 satellite crosses the Earth’s magnetopause near the subsolar point. The investigation focuses on the possible existence of a particular type of distribution that would be associated with a source of energetic particles in the high-latitude magnetosphere. PADs, demonstrating broad, persistent field-aligned fluxes filling a single hemisphere (upper/northern or lower/southern), were observed just sunward of the magnetopause current layer for an extended period of many minutes. These distributions are a direct prediction of a possible source of energetic particles located in the high altitude dayside cusp and we present five examples in detail of the three-dimensional particle distributions to demonstrate their existence. From these results, other possible causes of such PADs are examined.Key words. Magnetospheric physics (energetic particles, precipitating; magnetopause, cusp and boundary layers; magnetospheric configuration and dynamics)
Highlights
The recent discovery by the Polar satellite that the high altitude dayside cusp may be the location of an acceleration mechanism capable of producing appreciable fluxes of 100 s to 1000 s of keV ions from the shocked solar wind entering the cusp has been reported by Chen and Fritz (1998); Chen et al (1997)
In the 5 cases presented here, in a seasonal, chronological order, the ISEE-1 Medium Energy Particles Experiment (MEPE) observed field-aligned fluxes of energetic ions just sunward of the magnetopause near the subsolar point, as the spacecraft transitioned from a region of open field line geometry to a closed, or trapped, geometry
The particle distributions were observed to be present for extended periods on open field lines, ranging from two to tens of minutes, which suggests that they are a common occurrence
Summary
The data set used is from the ISEE-1 spacecraft which was launched together with ISEE-2 on October 1977 into an elliptic orbit with an apogee of RE, a perigee of 280 km, a period of about 57 h, and an inclination of about 28◦. The Medium Energy Particles Experiment (MEPE) on ISEE-1 and 2 was designed to detect electrons and ions ranging from 22.5 keV to 1.2 MeV for electrons, and from 24 keV to 2 MeV for protons. This resulted in 96 samples being made on the 4π steradian unit sphere. As a point of information about the ISEE-1 MEPE, the instrument responses from the WAPS sensor were accumulated in a manner that was synchronized to the satellite spin period and not the satellite telemetry cycle.
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