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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 112,
A11202,
doi:10.1029/2007JA012369,
2007
Magnetic activity in the polar caps: Relation to sudden changes in the solar wind dynamic pressure
O. A. Troshichev
Department of Geophysics, Arctic and Antarctic Research Institute, St. Petersburg, Russia
A. S. Janzhura
Department of Geophysics, Arctic and Antarctic Research Institute, St. Petersburg, Russia
P. Stauning
Solar-Terrestrial Physics Division, Danish Meteorological Institute, Copenhagen, Denmark
Abstract
Response of the polar cap (PC) magnetic activity to sudden changes in solar wind dynamic pressure is analyzed with use of
the northern and southern polar cap indices for 1998–2002 and corresponding solar wind parameters: geoeffective interplanetary
electric field (Em) and the solar wind dynamic pressure (P SW), reduced to the magnetopause. Only sudden pressure pulses starting against the background of steady quiet pressure levels
were taken for the analysis. To separate effects produced by Em and P SW, we examined the behavior of the average characteristics P SW, Em, and PC under the different restrictions imposed in turn on (1) electric field Em, (2) magnitude of the pressure P SW after the jump, and (3) rate of the pressure increase (dP SW/dt), the other two quantities being kept invariant in so doing. The following results have been obtained. The electric field
Em determines behavior of the PC index, the value of which is directly influenced by the Em increase with a delay time of
about 15–30 min. The solar wind pressure growth rate (i.e., jump power dP SW/dt) appears to be the second most important factor for the PC index increase, the pressure gradient dP SW = 1 nPa being approximately equivalent to the action of dEm = 0.33 mV/m, with a delay time shortened up to a few minutes. The growth rate of the pressure gradient seems to be the
sole factor for the PC index increase under conditions of the northward interplanetary magnetic field B Z and for the PC index decrease after the dynamic pressure negative jump.
Received 24
February
2007;
accepted 26
June
2007;
published 3
November
2007.
Keywords: PC index;
solar wind dynamic pressure;
geoeffective electric field.
Index Terms: 2776 Magnetospheric Physics: Polar cap phenomena; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2134 Interplanetary Physics: Interplanetary magnetic fields; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions (2431); 2712 Magnetospheric Physics: Electric fields (2411).
Read Full Article (file size: 392060 bytes) Cited by
Citation: Troshichev, O. A., A. S. Janzhura, and P. Stauning
(2007),
Magnetic activity in the polar caps: Relation to sudden changes in the solar wind dynamic pressure,
J. Geophys. Res.,
112,
A11202,
doi:10.1029/2007JA012369.
Copyright 2007 by the American Geophysical Union.
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