Geomagnetic activity for northward interplanetary magnetic fields: Am index response

Journal Article · Sun Jul 01 04:00:00 EDT 1990 · Geophysical Research Letters (American Geophysical Union); (USA)

DOI:https://doi.org/10.1029/GL017i008p01065· OSTI ID:6514205

Scurry, L; Russell, C T ^[1]

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1. Univ. of California, Los Angeles (USA)

The Am index is used to study the response of the magnetosphere to northward IMF. It is shown that most of the observed increase in activity can be explained by a correlation of the solar wind dynamic pressure with the IMF field strength such that the Am index varies only slightly with northward IMF strength when the solar wind dynamic pressure is held constant. There remains a smaller response of Am to solar wind velocity, which is usually attributed to a viscous interaction of the solar wind with the magnetosphere such as through the Kelvin-Helmholtz instability. The diurnal variation of Am during northward fields is also examined. A model invoking the Kelvin-Helmholtz instability on the flanks of the magnetopause have been used to predict the annual behavior of this diurnal variation. The predicted annual behavior is not found for northward IMF. The difference in diurnal variation from summer months to winter months, suggested to be caused solely by the Kelvin-Helmholtz instability, appears only for southward fields.

• OSTI ID: 6514205
• Journal Information: Geophysical Research Letters (American Geophysical Union); (USA), Journal Name: Geophysical Research Letters (American Geophysical Union); (USA) Vol. 17:8; ISSN 0094-8276; ISSN GPRLA
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANNUAL VARIATIONS
DAILY VARIATIONS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ENERGY TRANSFER
GEOMAGNETIC FIELD
HELMHOLTZ INSTABILITY
INSTABILITY
INTERACTIONS
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC BAYS
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOPAUSE
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
SOLAR ACTIVITY
SOLAR WIND
VARIATIONS