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Gyrophase‐restricted 100 keV–2 MeV ion beams near the foreshock boundary
Author(s) -
Meziane K.,
Wilber M.,
Lin R. P.,
Parks G. K.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2003gl017592
Subject(s) - foreshock , physics , gyroradius , ion , solar wind , atomic physics , range (aeronautics) , earth radius , nuclear physics , plasma , magnetosphere , aftershock , materials science , geology , quantum mechanics , seismology , composite material
We report on gyrophase‐restricted ion beams with energies extending from ∼100 keV up to ∼2 MeV, observed by Wind in the Earth's distant (∼65 R E ) foreshock. The ion gyrophases seen were nearly constant during periods when the distance to the shock contact point could be expected to vary by several R E , when there was no significant wave activity. At times the distributions had two peaks ∼180° apart in gyrophase. These were consistent with a remotely‐sensed energetic ion foreshock region having a thickness <2 gyroradii (∼1.5 R E for 0.5 MeV protons with pitch‐angle α = 30°). In this picture, gaps in phase space would correspond to particles with guiding centers outside of the energetic foreshock region. Similar observations over a decade of energies (100 keV–2 MeV) suggest that the region thickness scales with gyroradius. According to this interpretation, we have determined a rough range of geometries for which energetic particle production is favored. (Eg., θ B n ∼70–80° for 500 keV ions with α = 30°.)