Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

Details Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11601207l&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue A1, CiteID A01207

Physics

Magnetospheric Physics: Substorms, Magnetospheric Physics: Magnetic Storms And Substorms (4305, 7954), Ionosphere: Ionospheric Dynamics, Planetary Sciences: Solid Surface Planets: Polar Regions, Interplanetary Physics: Interplanetary Magnetic Fields

Scientific paper

An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

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