Publication Date:
2017-11-07
Description:
Dropouts in electron fluxes at L ∼ 4.2 were investigated for a broad range of energies from 120 keV to 10 MeV, using 16 years of electron flux data from Combined X-ray Dosimeter (CXD) onboard Global Positioning System (GPS) satellites. Dropouts were defined as flux decreases by at least a factor 4 in 12 hours, or 24 hours during which a decrease by at least a factor of 1.5 must occur during each 12-hours time bin. Such fast and strong dropouts were automatically identified from the GPS electron flux data and statistics of dropout magnitudes and occurrences were compiled as a function of electron energy. Moreover, the Error Reduction Ratio (ERR) analysis was employed to search for nonlinear relationships between electron flux dropouts and various solar wind and geomagnetic activity indices, in order to identify potential external causes of dropouts. At L ∼ 4.2, the main driving factor for the more numerous and stronger 1-10 MeV electron dropouts turns out to be the southward Interplanetary Magnetic Field B s , suggesting an important effect from precipitation loss due to combined EMIC and whistler-mode waves in a significant fraction of these events, supplementing magnetopause shadowing and outward radial diffusion which are also effective at lower energies.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
