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Observation of relativistic electron precipitation during a rapid decrease of trapped relativistic electron flux
Author(s) -
Millan R. M.,
Lin R. P.,
Smith D. M.,
McCarthy M. P.
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl028653
Subject(s) - electron precipitation , physics , flux (metallurgy) , van allen radiation belt , electron , bremsstrahlung , precipitation , atomic physics , astrophysics , magnetosphere , computational physics , geophysics , nuclear physics , plasma , meteorology , chemistry , organic chemistry
We present the first quantitative comparison of precipitating and geomagnetically trapped electron flux during a relativistic electron depletion event. Intense bremsstrahlung X‐ray emission from relativistic electron precipitation was observed on January 19–20, 2000 (21:20–00:45 UT) by the germanium spectrometer on the MAXIS balloon payload (−7.2 to −9.3 E, 74 S corresponding to IGRF L = 4.7, 1920–2240 MLT). A rapid decrease in the geosynchronous >2 MeV electron flux was simultaneously observed at GOES‐8 and GOES‐10, and between 0.34–3.6 MeV by GPS ns33 at L = 4.7. The observations show that electrons were lost to the atmosphere early in the flux depletion event, during a period of magnetic field stretching in the tail. The observed X‐ray spectrum is well modeled by an exponential distribution of precipitating electrons with an e‐folding energy of 290 keV and a lower‐energy cut‐off of 400 keV. The duration of the event implies precipitation extended over at least 3 hours of MLT, assuming a source fixed in local time. Comparison of the precipitation rate with the flux decrease measured at GPS implies that the loss cone flux was only ∼1% of the equatorial flux. However, precipitation is sufficient to account for the rate of flux decrease if it extended over 2–3 hours of local time.