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Magnetospheric electric field variations caused by storm-time shock fronts |
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| Authors: | M Kokorowski EA Bering III M Ruohoniemi JG Sample RH Holzworth SD Bale JB Blake AB Collier ARW Hughes EH Lay RP Lin MP McCarthy RM Millan H Moraal TP O’Brien GK Parks M Pulupa BD Reddell DM Smith PH Stoker L Woodger |
| Institution: | 1. University of Washington, Department of Earth and Space Sciences, Seattle, WA 98195, USA;2. Physics Department, University of Houston, 617 Science and Research I, Houston, TX 77204-5005, USA;3. Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA;4. University of California at Berkeley, Space Sciences Laboratory, Berkeley, CA 93923, USA;5. Aerospace Corporation, Box 92957, Los Angeles, CA 90009-2957, USA;6. University of KwaZulu-Natal, Physics Department, Durban 4001, South Africa;g Dartmouth College, Department of Physics and Astronomy, Hanover, NH 03755, USA;h North-West University, School of Physics, Potchefstroom 2520, South Africa;i University of California at Santa Cruz, SCIPP, Santa Cruz, CA 95064, USA |
| Abstract: | On January 20, 2005 there was an X 7.1 solar flare at 0636 UT with an accompanied halo coronal mass ejection (CME). The resultant interplanetary shock impacted earth ∼36 h later. Near earth, the Advanced Composition Explorer (ACE) spacecraft observed two impulses with a staircase structure in density and pressure. The estimated earth-arrival times of these impulses were 1713 UT and 1845 UT on January 21, 2005. Three MINIature Spectrometer (MINIS) balloons were aloft on January 21st; one in the northern polar stratosphere and two in the southern polar stratosphere. MeV relativistic electron precipitation (REP) observed by all three balloons is coincident (<3 min) with the impulse arrivals and magnetospheric compression observed by both GOES 10 and 12. Balloon electric field data from the southern hemisphere show no signs of the impulse electric field directly reaching the ionosphere. Enhancement of the balloon-observed convection electric field by as much as 40 mV/m in less than 20 min during this time period is consistent with typical substorm growth. Precipitation-induced ionospheric conductivity enhancements are suggested to be (a) the result of both shock arrival and substorm activity and (b) the cause of rapid (<6 min) decreases in the observed electric field (by as much as 40 mV/m). There is poor agreement between peak cross polar cap potential in the northern hemisphere calculated from Super Dual Auroral Radar Network (SuperDARN) echoes and horizontal electric field at the MINIS balloon locations in the southern hemisphere. Possible reasons for this poor agreement include (a) a true lack of north–south conjugacy between measurement sites, (b) an invalid comparison between global (SuperDARN radar) and local (MINIS balloon) measurements and/or (c) radar absorption resulting from precipitation-induced D-region ionosphere density enhancements. |
| Keywords: | Electric field Convection Substorm Relativistic electron precipitation Shock wave |
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