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Quantitative separation of the directly‐driven and unloading components of the ionospheric electric field
Author(s) -
Sun W.,
Zhou X.Y.,
Du A.
Publication year - 2008
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 - 10.1029/2008gl033931
Subject(s) - substorm , sawtooth wave , electric field , ionosphere , geophysics , midnight , geology , convection , meteorology , physics , geodesy , plasma , magnetosphere , computer science , astronomy , quantum mechanics , computer vision
It is well known that the ionospheric electric field turns to southward in the auroral zone midnight sector at a substorm expansion phase onset. This letter reports a study of quantitatively separating the southward electric field ( Es ) from the total electric field by using the Natural Orthogonal Components (NOC) algorithm. The Es will be regarded as an unloading component of substorms. The westward component of the electric filed ( Ew ) in the midnight sector, which is associated with two‐cell convection, is identified as a directly driven component of substorms. Separated results for the event on April 18, 2002 are shown in the present study, which are characterized as a sawtooth event. It is found that the Es increased significantly to 30–40 mV/m during substorm expansion phases. Substorms may not develop if Es/Ew < 1 and Es < ∼30 mV/m during the sawtooth event.