Penetration Electric Field Observations and Modeling in the Pre-Noon Mid-Latitude Ionosphere
Abstract
We have studied the mid-latitude ionospheric response to a large geomagnetic storm that occurred on 11 April 2001. The storm main phase began at about 1600 UT, and by 1630 UT, two western U.S. ionosondes (Bear Lake, UT, and Boulder, CO; a separation of 700 km) began recording similar, periodic (~ 1 hr) oscillations in hmF2. Both stations were in the pre-noon sector at the start of the event. The fluctuations lasted the rest of the UT day, and the vertical displacements were up to 100 km (virtual height). Significant IMF Bz oscillations are evident in the WIND data during this same period, but the IMF and hmF2 time series exhibit a phase difference that varies in time as the event progresses. We attribute the rapid vertical F-layer motions to ExB drifts associated with zonal penetration electric fields. To test this hypothesis, we derived the zonal fields from the Boulder ionosonde data, and used these fields to drive the Utah State Time-Dependent Ionospheric Model (TDIM). The modeled hmF2 values matched well with the Boulder observations. However, the modeled foF2 oscillations are somewhat out-of-phase with, and have smaller amplitudes than, the Boulder data; the cause of this is still under study. We have also examined DMSP data for this storm, which revealed strong pre-noon vertical ion drifts and Birkeland currents in an F15 pass at the start of the event, as well as the signature of dusk meridional penetration fields in the F13 SSJ/4 data throughout the storm. Finally, we consider whether our zonal penetration field time series could be caused by the ionospheric closure of the storm-time asymmetric ring current.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMSM22A0558N
- Keywords:
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- 2411 Electric fields (2712);
- 2431 Ionosphere/magnetosphere interactions (2736);
- 2435 Ionospheric disturbances;
- 2443 Midlatitude ionosphere;
- 7843 Numerical simulation studies