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| Titel |
Pc5 modulation of high energy electron precipitation: particle interaction regions and scattering efficiency |
| VerfasserIn |
E. Spanswick, E. Donovan, G. Baker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 23, no. 5 ; Nr. 23, no. 5 (2005-07-27), S.1533-1542 |
| Datensatznummer |
250015243
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| Publikation (Nr.) |
 copernicus.org/angeo-23-1533-2005.pdf |
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| Zusammenfassung |
| Using the NORSTAR riometer and CANOPUS magnetometer arrays we have
investigated the modulation of high energy electron precipitation by
ULF waves in the Pc5 frequency band. We conducted two separate
studies of Pc5 activity in the riometers. The first is an
independent survey of three riometer stations in the Churchill line
(one at each sub-auroral, auroral, and typical polar cap boundary
latitudes) in which we identified all riometer Pc5-band pulsations
over 11 years. All had a corresponding magnetometer pulsation
implying that a magnetic pulsation, is a necessary condition for a
riometer pulsation (in the Pc5 Band). We find seasonal and latitude
dependencies in the occurrence of riometer pulsations. By a factor of
two, there are more riometer pulsations occurring in the fall-winter
than the spring-summer. At higher latitudes there is a tendency
towards noon pulsations during the spring-summer, suggesting that the
criteria for riometer pulsations is affected by the dipole tilt. Our
second study was based on the previous magnetometer study of
Baker et al. (2003). Using the database of Pc5 activity from that study we
were able to select the riometer Pc5 pulsations which adhere to the
strict Pc5 definition in the magnetometer. We find that roughly 95%
of the riometer pulsations occurred in the morning sector compared
to 70% in the magnetometer. Given a magnetometer pulsation at
Gillam in the morning sector, there is a 70% chance of there being
a corresponding riometer pulsation. The morning sector probabilities
at Rankin (geomagnetic (PACE) latitude 74°) and Pinawa
(61°) are 3% and 5%, respectively. These statistics suggest
there is a localized region in the pre-noon magnetosphere where Pc5
band ULF activity can modulate high energy electron precipitation.
We also find that riometer pulsations display a Kp selection towards
mid (i.e. 3–4) activity levels which mimics the product of the Kp
dependence of high-energy electron fluxes on the dawn side (from
CRRES) and all magnetic Pc5 activity. A superposed epoch analysis
revealed that the elevated electron flux needed to produce a
riometer pulsation is most likely provided by substorm injections on
the nightside. We also find that the amplitude of modulated
precipitation correlates well with the product of the background
absorption and the magnetic pulsation amplitude, again leading to
the idea that a riometer pulsation needs both favorable
magnetospheric electron flux conditions and large enough magnetic
Pc5 wave activity. We further separate our pulsations into field
line resonances (FLRs), and non-field line resonances (non-FLRs), as
identified in the Baker et al. (2003) survey. We find that FLRs are more
efficient at modulating particle precipitation, and non-FLRs display
an amplitude cutoff below which they do not interact with the high
energy electron population. We conclude that the high energy
electron precipitation associated with Pc5 pulsations is caused by
pitch angle scattering (diffusion) rather than parallel
acceleration. We suggest two future studies that are natural
extensions of this one.
Keywords. Energetic Particles/Precipitating; Wave-Particle
Interactions; Auroral Phenomena |
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