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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).

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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.