Energy and pitch-angle dispersions of LLBL/cusp ions seen at middle altitudes: predictions by the open magnetosphere model
Numerical simulations are presented of the ion distribution functions seen by middle-altitude spacecraft in the low-latitude boundary layer (LLBL) and cusp regions when reconnection is, or has recently been, taking place at the equatorial magnetopause. From the evolution of the distribution func...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
1997-12-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/15/1501/1997/angeo-15-1501-1997.pdf |
| Summary: | Numerical simulations are presented of the
ion distribution functions seen by middle-altitude spacecraft in the
low-latitude boundary layer (LLBL) and cusp regions when reconnection is, or has
recently been, taking place at the equatorial magnetopause. From the evolution
of the distribution function with time elapsed since the field line was opened,
both the observed energy/observation-time and pitch-angle/energy dispersions are
well reproduced. Distribution functions showing a mixture of magnetosheath and
magnetospheric ions, often thought to be a signature of the LLBL, are found on
newly opened field lines as a natural consequence of the magnetopause effects on
the ions and their flight times. In addition, it is shown that the extent of the
source region of the magnetosheath ions that are detected by a satellite is a
function of the sensitivity of the ion instrument . If the instrument one-count
level is high (and/or solar-wind densities are low), the cusp ion precipitation
detected comes from a localised region of the mid-latitude magnetopause (around
the magnetic cusp), even though the reconnection takes place at the equatorial
magnetopause. However, if the instrument sensitivity is high enough, then ions
injected from a large segment of the dayside magnetosphere (in the relevant
hemisphere) will be detected in the cusp. Ion precipitation classed as LLBL is
shown to arise from the low-latitude magnetopause, irrespective of the
instrument sensitivity. Adoption of threshold flux definitions has the same
effect as instrument sensitivity in artificially restricting the apparent source
region<br><br><b>Key words.</b> Low-latitude boundary layer · Cusp regions
· Open magnetosphere model · Mid-altitudes |
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| ISSN: | 0992-7689 1432-0576 |