Open AccessExamination of the storm/substorm relationship using global auroral X‐ray images
Author(s) -
Anderson P. C.,
Chen M. W.
Publication year - 2002
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001ja009184
Subject(s) - substorm , ionosphere , physics , noon , midnight , geophysics , atmospheric sciences , electric field , geomagnetic storm , polar , magnetosphere , environmental science , earth's magnetic field , astrophysics , magnetic field , astronomy , quantum mechanics
Global measurements by the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) instrument on board NASA's Polar spacecraft of the auroral X‐ray emissions associated with substorms show significant differences between isolated substorms and those occurring during geomagnetic storms. During isolated substorms at substorm onset the emissions are initially seen in the premidnight‐to‐midnight sector and then spread toward dawn. The emissions extend beyond 12 magnetic local time (MLT) with the most intense emissions occurring in the postdawn sector. The timescales for the appearance of X‐ray emissions in the various morningside MLT sectors are consistent with the drift times of electrons, of energies that produce the photons observed by PIXIE, under the influence of a magnetospheric electric field inferred from ionospheric ion drift measurements. During substorm recovery, emissions die away gradually at increasing MLT values with the last of the emissions in the noon sector disappearing several hours (∼3–4) after substorm onset. During the stormtime substorms, onset‐associated emissions are seen in the premidnight‐to‐midnight regions and spread toward dawn as in the isolated substorms. However, the emissions do not reach much beyond ∼9–10 MLT and very intense emissions are seen in the predawn MLT sectors. These intense predawn emissions are seen throughout the stormtime periods and are associated with significantly enhanced magnetospheric convection. There are brief reductions in intensity in the morningside emissions shortly after substorm onset consistent with a brief reduction in the cross‐tail electric field, followed by intensification again in the predawn sector on a timescale consonant with drifting electrons under the influence of a magnetospheric electric field. We conclude that the differences between the temporal evolution and morphology of the auroral X‐ray emissions during isolated and stormtime subtorms are the result of pitch angle scattering mechanisms whose MLT distribution and intensity are dependent on the strength of the magnetospheric electric field.