The Relationship between Ion and Electron Precipitation Patterns and Field-Aligned Current Systems During a Substorm
- Joseph R. Kan,
- Thomas A. Potemra,
- Susumu Kokubun and
- Takesi Iijima
Published Online: 19 MAR 2013
Copyright 1991 by the American Geophysical Union.
How to Cite
Iijima, T., Watanabe, M., Potemra, T. A., Zanetti, L. J. and Rich, F. J. (1991) The Relationship between Ion and Electron Precipitation Patterns and Field-Aligned Current Systems During a Substorm, in Magnetospheric Substorms (eds J. R. Kan, T. A. Potemra, S. Kokubun and T. Iijima), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM064p0097
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900308
Online ISBN: 9781118663981
- Magnetospheric substorms—Congresses
We show in this study the persistency of large-scale characteristics in auroral particle precipitation patterns during a prolonged disturbed period which included a growth phase and multiple expansion onsets. The north-south conjugacy of these patterns and their relationship with the field-aligned currents are also discussed. We have investigated these characteristics by using the magnetic field and the plasma measurements acquired with the DMSP F7 satellite at an altitude of ∼840 km, and in the pre-midnight MLT sector. Principal characteristics determined here include the following: (1) The plasma precipitation characteristics during substorms consist of three distinctive patterns, or parts that are denoted here as “C”, “B”, and “A” from the lowest latitude, respectively, for both the ions and electrons; (2) The C plasma precipitation pattern is characterized by a double-energy composite structure of the ions that comprises the high-energy component (energy>a few keV) and the low-energy component (<a few keV). Its high-latitude limit is indicative of the outer boundary in the magnetosphere of the ion low- energy component domain, and the outer boundary of the earthward injecting plasma. Both of these moved toward the earth throughout the course of a prolonged disturbed period. The C pattern is thought to be the quasi-persistent core part of the plasma precipitation; (3) The B plasma precipitation pattern occurs poleward of C. The B pattern is primarily characterized by a highly structured intensity enhancement in the E-t spectrum of both the ions and electrons, which included the features suggestive of an existence of field-aligned electric field directed toward and away from the earth. The B pattern expanded drastically over a much wider latitudinal span, especially after the onset of substorm expansion phase through the recovery phase, and is thought to be the explosive part of the plasma precipitation; (4) At the polewardmost latitude of the plasma precipitation (adjacent to and poleward of B), there exists a distinctive part, A that is principally characterized by its association of a field-aligned flow of the ions. The A pattern was not recognizable during the growth phase, but occurred exclusively after the onset of substorm expansion phase; (5) A general relationship between the field-aligned currents and the plasma precipitation was evident for both the northern and southern hemisphere. Namely, the traditional Region 2 current system nearly was associated with the C part (quasi-persistent core part) and the traditional Region 1 current system was associated mostly with the B part (explosive part) of the plasma precipitation; (6) In the same premidnight MLT sector, the observed field-aligned currents above the northern (winter) polar ionosphere had the normal pattern for the evening-side traditional Region 2 and Region 1 current systems. Whereas, above the southern (summer) polar ionosphere, the observed field-aligned currents had the morning-side pattern of the traditional Region 2 and Region 1 current systems (with the morning-side pattern overlapping with the evening-side pattern at the equatorwardmost latitudes).