Implications of unusual pitch-angle distributions observed by ISEE-1 and ISEE-2.

Details Implications of unusual pitch-angle distributions observed by ISEE-1 and ISEE-2. Implications of unusual pitch-angle distributions observed by ISEE-1 and ISEE-2.

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm21b0208z&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM21B-0208

Physics

2744 Magnetotail

Scientific paper

Unusual energetic particle Pitch Angle Distributions (PADs) were found on the night side tail of the earth's magnetosphere using data collected by the ISEE-1 and ISEE-2 satellites. The study was carried out between the hours of 0800-1330 UT on March 3rd, 1979. ISEE-1 was at 3MLT and a radial distance of 15 RE at 1000 UT, when the unusual PADs began to be observed. The period of the observations shows an isotropic increase in the energy ranges 22.5-189 keV for electrons, and 24-142 keV for protons. In the first electron energy channel (22.5-39 keV), the isotropic increase in the intensity of these particles stops for those particles with 90-degree pitch angles before those with parallel/anti-parallel pitch angles (0-30deg.), producing the minimum flux at 90 degrees pitch angles. The resulting PAD is known as a Butterfly PAD. The same is observed for the proton channels P1 through P4. In electron channels E2, E3, E4, we observed something different. Here when the 0-30 pitch angles start to level off, there was a sudden flux drop in the near perpendicular particles producing also the Butterfly PADs. In some channels, the drop in flux is over an order of magnitude. The period for these butterfly distributions is of about 2 hours in the electron channels, and 2« hours for the protons. After that time period, the fluxes changed from butterfly PADs to isotropic PADs. Towards the beginning of the time period studied, we observe the existence of peaked-at-90 degree, isotropic, and butterfly PAD occurring respectively in E1, E2, E3 at the same time and location with the only variable being the respective energy of the electrons being measured. The observations made by ISEE-2 are somewhat different than those made by ISEE-1. ISEE-2 does see a higher flux in the 0-30 degree pitch angles in the protons only, but the ISEE-2 sensors did not resolve the PAD as a function of energy and therefore the energy-integrated PADs are not as clear as those of the ISEE-1 satellite. At 1000 UT, ISEE-2 is at 3.5MLT and a radial distance of 12 RE. The differences and physical implications between ISEE-1 and ISEE-2 will be presented and discussed in detail. During the time period studied, the geomagnetic conditions were rather quiet, and LANL geosynchronous satellites observed no substorms.

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