Typical and Atypical Magnetospheric SI and SSC Responses to Interplanetary Shocks

Details Typical and Atypical Magnetospheric SI and SSC Responses to Interplanetary Shocks Typical and Atypical Magnetospheric SI and SSC Responses to Interplanetary Shocks

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm53a..01c&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM53A-01

Physics

2721 Field-Aligned Currents And Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions (2431), 2740 Magnetospheric Configuration And Dynamics, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Interplanetary shocks are associated with sudden changes in solar wind dynamic pressure. Sudden increases in solar wind dynamic pressure cause a sudden increase in the low latitude geomagnetic field measured by ground magnetometers called sudden impulses (SI) or storm sudden commencements (SSC) when followed by a geomagnetic storm. We propose here that the SI or SSC reaction depends upon conditions in the interplanetary magnetic field (IMF) and in the magnetosphere-ionosphere system. The typical SI response of the low-latitude northward magnetic field at the Earth's surface is a world-wide simultaneous jump in magnitude with a slightly larger jump near local noon. This response is attributed to the enhanced Chapman Ferraro currents that develop to achieve the compressed magnetosphere. However, we have found several atypical cases where the largest enhancement of the disturbance are observed on the night side with little or no field increase near local noon. To achieve such an atypical response we suggest the formation of current system with inward high latitude field-aligned current on the dawn side of the Earth and outward field-aligned current on the dusk side of the Earth. The field-aligned currents produce a magnetic perturbation field that is in the negative X direction on the dayside and positive X direction on the night side, thus adding destructively to the SI disturbance on the day side and constructively on the night side. We find that several cases of atypical SI or SSC where the IMF turns northward from a near zero value. In this case the field-aligned currents are associated with the formation of the NBZ current system. The field-aligned currents for this `transition' current system at dusk and dawn connect poleward through the ionosphere with the newly forming NBZ field-al;igned current system. In addition, a new case has been found where the dynamic pressure increase is not associated with a simultaneous IMF northward rotation. Rather, it occurs during a smoothly increasing negative IMF Bz component. In this case, we propose, the field-aligned currents at dawn and dusk must connect via the ionosphere through a high conductivity Cowling channel that has formed during the previous strong driving by the southward IMF prior to the shock encounter with the magnetosphere.

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