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Evolution of auroral asymmetries in the conjugate hemispheres during two substorms
Author(s) -
Østgaard N.,
Humberset B. K.,
Laundal K. M.
Publication year - 2011
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 - 10.1029/2010gl046057
Subject(s) - substorm , magnetic field , physics , geophysics , interplanetary magnetic field , electric field , field line , orientation (vector space) , phase (matter) , astrophysics , geodesy , computational physics , geology , solar wind , magnetosphere , geometry , mathematics , quantum mechanics
Five hours of simultaneous global imaging data from the conjugate hemispheres are used to examine the dynamics of the auroral substorm. Earlier studies have demonstrated that substorm onset locations in the two hemispheres are systematically displaced due to the orientation of the interplanetary magnetic field. In this paper we present, for the first time, how the asymmetric auroras induced by the IMF orientation at substorm onset disappears during the expansion phase. We suggest that this is the large scale manifestation of auroral arcs as being the sites of magnetic stress release. Magnetic stress on field lines with asymmetric footpoints can lead to a net hemispherical difference in parallel electric field strength which implies that the auroras move with different speeds in the two hemispheres to release the magnetic stress. The relative velocity can be derived from the potential between the hemispheres. During expansion phase the twisted magnetic fields are rectified, bringing the closed magnetic field lines back to the configuration defined by the Earth's interior.