Ionospheric and stratospheric electric field responses to an extreme
solar energetic particle event
Abstract
This paper will report on the effects of an extreme space weather event.
On January 20th, 2005, a balloon-borne experiment
intended to measure relativistic electron precipitation and its effects
was aloft over Antarctica (~32 km; near 70º S, 345º W
geographic) throughout the duration of the solar energetic particle
(SEP) event. The balloon carried an x-ray scintillation counter, dc
electric field, and scalar electrical conductivity sensors. Intense
energetic proton precipitation and large increases in the energetic
proton population of the outer radiation belts were observed by a global
array of observatories and spacecraft. The stratospheric conductivity
increased by nearly a factor of 20 above ambient at the time of the SEP
event onset and returned to within a factor of two above normal levels
within 17 hours. The electric field decreased to near zero following the
increase in particle flux at SEP onset. Combined with an atmospheric
electric field mapping model, these data are consistent with a shorting
out of the global electric circuit and point toward substantial
ionospheric convection modifications. It is shown that the conductivity
profile predicted by the Sodankylä Ion and Neutral Chemistry (SIC) model
does not shield the balloon payload at 32 km from the ionospheric
horizontal field. Thus, the data really do indicate a very low level of
ionospheric convection over the balloon during the 6 hours following the
SEP event. We have used global magnetometer and satellite data to
interpret the changes in the vertical field as indicators of large scale
convection changes.