Parameterization of a cross polar cap potential decrease during a hard solar energetic particle event using the Hill saturation model

Details Parameterization of a cross polar cap potential decrease during a hard solar energetic particle event using the Hill saturation model Parameterization of a cross polar cap potential decrease during a hard solar energetic particle event using the Hill saturation model

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa23a1124k&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA23A-1124

Physics

2431 Ionosphere/Magnetosphere Interactions (2736), 2475 Polar Cap Ionosphere, 7513 Coronal Mass Ejections (2101), 7514 Energetic Particles (2114)

Scientific paper

The 20 January 2005 solar energetic particle (SEP) event was one of the hardest on record with the largest ground level (neutron monitor) event since 1956. On this day, the MINIS balloon campaign had one payload with electric field instrumentation aloft in the stratosphere above Antarctica at 71° S, 10° W geographic. When the SEPs arrived at earth, the horizontal electric field measured in the stratosphere by the MINIS balloon payload, which is characteristic of overhead large-scale ionospheric electric fields, rapidly (less than 3 minutes) decreased from 15 mV/m to near 0 mV/m as both pole-ward and east-ward components essentially vanished. The balloon payload measured a coincident 20-fold increase in electrical conductivity. As SEP flux declined, both the horizontal electric field and conductivity approached pre-SEP values until bulk coronal mass ejection plasma arrived the following day. In order to understand what physical mechanisms caused the horizontal electric field to vanish at SEP arrival, we examine the 20 January 2005 event using the Hill model which defines a saturation potential that limits the cross polar cap potential. Northward IMF and tenuous solar wind density ( less than 0.5 cm-3) combine to form a circumstance where the cross polar cap potential is low (less than 50 kV). According to the Hill model, the saturation potential is a function of the height-integrated ionospheric Pedersen conductivity. A rapid SEP-induced ionospheric conductivity enhancement creates a situation where saturation is meaningful. By using ion density output from the Sodankylä Ion Chemistry model, we investigate how the rapid ionospheric conductivity enhancement on 20 January 2005 can decrease the saturation potential, thus limiting the cross polar cap potential, and we compare the results to the MINIS balloon electric field measurements.

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