Implications of unusual pitch-angle distributions observed by ISEE-1 and 2C. A. Zuluaga, E. S. Beiser, J. Chen, and T. A. FritzCenter for Space Physics, Boston University, Boston MA, USA
Abstract. Unusual energetic particle pitch angle distributions (PADs) were observed
by the ISEE-1 and 2 satellites at 3 h MLT and a radial distance of about
10–15 RE during the time period of 07:00-14:00 UT on 3 March 1979.
The ISEE-1 satellite obtained complete 3-D
distributions of energetic proton and electron fluxes as a function of energy,
while ISEE-2 was configured to provide higher time resolution but less angular
resolution than ISEE-1. The ISEE-1 observed a butterfly PAD (a minimum in the
90° PA particle flux) for a period of about 2 h (10:00–12:00 UT)
for the electrons, and 3 h (09:00–12:00 UT) for the protons
over an energy range of 22.5–189 keV (E1–E4) for the electrons
and 24–142 keV (P1–P4) for the protons.
The small pitch angle (15°, 30°) charged particles (electrons and
protons) are seen to behave collectively in all four energy ranges.
The relative differences in electron fluxes between 15° PA and
90° PA are more significant for higher energy channels during the
butterfly PAD period.
Three different types of electron PADs (butterfly, isotropic, and
peaked-at-90°) were observed at the same location and time
as a function of energy for a short period of time before 10:00 UT.
Electron butterfly distributions were also observed by the ISEE-2 for about
1.5 h over 28–62 keV (E2–E4), although less well resolved than ISEE-1.
Unlike the ISEE-1, no butterfly distributions were resolved in the ISEE-2
proton PADs due to less angular resolution. The measured drift effects by
ISEE-1 suggest that the detected protons were much closer to the particle
source than the electrons along their trajectories,
and thus ruled out a nightside source within 18:00 MLT to 03:00 MLT.
Compared to 07:30 UT, the charged particle fluxes measured by ISEE-1
were enhanced by up to three orders of magnitude during the period 08:30–12:00 UT.
From 09:10:00 UT to 11:50 UT, the geomagnetic conditions were quiet
(AE<100 nT), the LANL geosynchronous satellites observed no substorms,
and the local magnetic field measured by ISEE-1 was almost constant,
while the small PA charged particle (both electron and proton) fluxes
measured by ISEE-1 increased gradually, which
implies a particle source other than the substorm source.
Based on detailed particle trajectory tracings in a realistic geomagnetic
field model, the 50–200 keV protons with small PA at 10:00 UT ISEE-1 location
on 3 March 1979 were passing through the northern high-altitude and high-latitude
morningside region where the cusp should be located under a dawnward IMF
component
condition, while those protons with large PA may connect to the high-latitude
morningside magnetopause. It is possible that the cusp source is responsible
for the all particles observed during the event.
Full Article (PDF, 2233 KB)
Citation: Zuluaga, C. A., Beiser, E. S., Chen, J., and Fritz, T. A.: Implications of unusual pitch-angle distributions observed by ISEE-1 and 2, Ann. Geophys., 24, 3099-3113, 2006. Bibtex EndNote Reference Manager