 |
| Titel |
One-two hour scale evolution of the inner magnetospheric plasma |
| VerfasserIn |
Masatoshi Yamauchi, Iannis Dandouras, Henri Rème, Rickard Lundin |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074411
|
|
|
|
|
|
| Zusammenfassung |
| In the inner magnetosphere inside the geosynchronous orbit, energy-latitude patterns of
trapped low-energy ring current ions (eastward drifting energy domain of less than 5 keV) are
normally north-south symmetric because these ions are bouncing between southern and
northern hemispheres with short bouncing periods (only about 10 minutes for 100 eV proton
and 1 minutes for 10 keV protons at L=4). Therefore, for inner magnetospheric phenomena
with longer time scale than few tens minutes, one can ignore the hemispheric difference when
examining temporal changes of the ion distribution at a fixed latitude (or L value) and
longitude. This fact gives an advantage to Cluster that has relatively quick perigee
traversals and nearly north-south symmetric orbits, i.e., along nearly the same longitude
(longitudinal difference between inbound and outbound is less than 1-2 hours) during
2001-2006. Therefore, any significant asymmetry in the ion energy-latitude pattern
observed during the Cluster perigee traversals during 2001-2006 means a temporal
effect such as ion energization, transport, or loss, with the time scale of order of an
hour.
After removing traversals in which ion data are severely contaminated by the radiation
belt particles (about one third of all traversals), e took statistics the inbound-outbound
asymmetry of the ion population and its energy-latitude patterns at low energy (less than
several keV) for the remaining 494 perigee traversals of Cluster spacecraft 4 during
2001-2006. As the baseline, we considered the following two ion populations that are
commonly found in Cluster data: (1) Wedge-like energy-latitude structure at sub-keV range.
(2) Similar to the wedge-like structure but dispersion is weak (nearly vertical in the
spectrogram) and the energy range extends from the about 10 keV to sub-keV (Yamauchi et
al., 2006).
For both types, the asymmetric cases are observed more frequently than the
symmetric cases at all local time. The excess of the asymmetric case is reasonable for
the second type that is most frequently observed at post-midnight because at this
population is most likely related to the substorm injection. However, the excess of the
asymmetric case for the wedge-like structure (first type) is unexpected because it is
formed after long-time drift with slow drifting velocity. The peak local time for the
asymmetric wedge-like structure is morning, whereas symmetric case is peaked at
prenoon. |
|
|
|
|
|
|