Polar cusp topology and position as a function of interplanetary magnetic field and magnetic activity: Comparison of a model with Viking and other observations

Journal Article · Sun Sep 01 04:00:00 EDT 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA01420· OSTI ID:5180663

Stasiewicz, K ^[1]

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1. Swedish Inst. of Space Physics, Uppsala (Sweden)

A family of quantitative magnetospheric models is used to determine the cusp position in the ionosphere and to analyze the field topology around the outer cusp. It is demonstrated that the cusp proper, observed in particle precipitation patterns, can be defined as the footprint of the magnetopause current layer with field lines connected to the interplanetary medium via a normal magnetic field component. It is suggested that the finite-sized physical cusp originates as a result of gyroviscous erosion at the magnetopause current layer that enlarges the topologically singular magnetic cusp. The model-predicted magnetic latitude (MLAT) of the ionospheric footprint of the cusp is 79 during quiet conditions and 74 during active periods. The latitude of the cusp varies also with universal time and with season, due to variation of the dipole tilt angle. The corrected magnetic coordinates are found to exhibit the smallest amplitude of diurnal variation of the cusp position and are recommended for mapping of auroral phenomena. An interplanetary magnetic field (IMF) B{sub y} component linearly superposed with the magnetospheric field can shift the magnetic local time of the cusp by a maximum of 0.07-0.15 hour/nT. A negative (positive) IMF B{sub z} component can shift equatorward (poleward) the position of the cusp by a maximum of 0.1-0.2/nT. A similar effect is obtained with a positive (negative) B{sub x} component. These results imply that the instantaneous effect of a negative B{sub z} component on the equatorward shift of the cusp is smaller than an indirect effect due to increased magnetic activity.

• OSTI ID: 5180663
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 96:A9; 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
COMPARATIVE EVALUATIONS
COORDINATES
DAILY VARIATIONS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
EVALUATION
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC FIELDS
MAGNETOPAUSE
MATHEMATICAL MODELS
MATHEMATICS
POLAR CUSP
SEASONAL VARIATIONS
TOPOLOGY
VARIATIONS