A theory of substorms: Onset and subsidence

Journal Article · Wed Jun 01 04:00:00 EDT 1988 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA093iA06p05624· OSTI ID:5181935

Kan, J R; Zhu, L; Akasofu, S I ^[1]

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1. Univ. of Alaska, Fairbanks (USA)

It is shown by a computer simulation study of the magnetosphere-ionosphere (M-I) coupling that an enhanced magnetospheric convection can lead to auroral substorm onset in about 40 min after a southward turning of IMF. The simulation results show that the enhanced M-I coupling can produce intense upward field-aligned currents in the midnight sector near the poleward boundary of a high-conductance belt associated with the diffuse auroral precipitation. Two necessary conditions for substorm onset are that (1) the polar cap potential must exceed a certain value and (2) the convection reversal region must overlap with the poleward gradient of the diffuse auroral conductance in the ionosphere in the midnight sector. The matching ensures that the divergence of the Pedersen current colocates with the divergence of the Hall current to maximize the upward field-aligned current near the poleward boundary of the diffuse aurora in the midnight sector for substorm onset. Without the matching, the auroral brightening would not occur, even if the electrojets are appreciable. Substorm subsides when one of the two necessary conditions is no longer satisfied. This can occur owing either to a northward turning of the IMF or weakening of Alfven shielding due to substorm enhancement of the ionospheric conductance during a prolonged southward IMF.

• OSTI ID: 5181935
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 93:A6; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAE
CHARGED-PARTICLE PRECIPITATION
COMPUTERIZED SIMULATION
CONVECTION
CURRENTS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
ELECTROJETS
ENERGY TRANSFER
EXPANSION
HEAT TRANSFER
INTERACTIONS
INTERPLANETARY MAGNETIC FIELDS
IONOSPHERE
MAGNETIC BAYS
MAGNETIC FIELDS
MASS TRANSFER
MATHEMATICAL MODELS
MORPHOLOGY
PHYSICAL PROPERTIES
PLANETARY IONOSPHERES
SIMULATION