Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh23a0329c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SH23A-0329
Physics
2431 Ionosphere/Magnetosphere Interactions (2736), 2716 Energetic Particles: Precipitating, 2774 Radiation Belts, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
At geostationary orbit radiation belt relativistic flux variations are the result of complex interplay between competing acceleration and loss mechanisms. It has been found that geomagnetic storms produce all possible responses in the outer belt flux levels, i.e., flux increases ~50%, flux decreases ~20%, and no change ~30%. Understanding these flux changes is important in developing theoretical models of the radiation belts. In this study we analyze ground-based ionospheric data during a sudden electron flux decrease observed at geosynchronous orbit. Previous estimates of the significance of REP into the atmosphere have relied upon point-measurements of precipitation from satellites or balloons. Here we make use of long range remote sensing to provide a regional indication of the importance of these loss processes. We use subionospheric VLF signals to determine the effect of the flux decrease event on the southern and northern hemisphere high latitude ionospheres in terms of enhanced energetic particle precipitation. We contrast the timing and location of precipitation events with preliminary observations of X-ray bursts from the same event made during the January 2005 "MINIS" balloon campaign. In January 21 a K{p}=8 geomagnetic storm occurred, leading to the relativistic electron drop-out at geosynchronous orbit starting at ~17:10 UT. GOES-10 and GOES-12 >2 MeV electron fluxes decreased by three orders of magnitude by 18 UT. GOES-12 saw the fastest change, i.e., a decrease of two orders of magnitude in 10 minutes. The MINIS balloon experiment has reported X-ray bursts produced by REP into the atmosphere above the balloons during this event around 17:10-17:20 UT [E. A. Bering III and the MINIS Team, IAGA Scientific Assembly 2005, IAGA2005-A-00631]. The relativistic electron drop-out occurred during the recovery from an unusually hard solar proton event that started on January 20, 2005. This lead to significant disturbances in the lower ionosphere, super-posed on the REP effects. Here we report on large-scale precipitation into the atmosphere observed in this time period. Three ground-based radio propagation experiments at L~5, 2 in the northern hemisphere, and 1 in the south, were monitoring the same longitude sector as GOES-12. The precipitation began at the same time as the geosynchronous flux decrease. Estimates suggest that the atmospheric precipitation was only a small fraction of the flux apparently lost (about 1/30) over this 10 minute period. However, continuing precipitation from 4< L<6, which was observed for 2.7 hours, dumps about 1/2 of the total relativistic electron content in the region. Very short-lived spike events were also observed during the flux decrease event. These are consistent with the expected impact of microbursts of relativistic electrons on the atmosphere. The short-lived events were concurrent with the longer-lasting burst events, but appear to contribute only a small fraction of the losses in this particular event.
Clilverd Mark A.
Rodger Craig J.
Seppälä Annika
Ulich Thomas
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