Electrodynamics of an Omega-Band and Comparison of Ground- and Space-Based Conductance Estimates

Details Electrodynamics of an Omega-Band and Comparison of Ground- and Space-Based Conductance Estimates Electrodynamics of an Omega-Band and Comparison of Ground- and Space-Based Conductance Estimates

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa33b1638k&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA33B-1638

Physics

2407 Auroral Ionosphere (2704), 2411 Electric Fields (2712), 2494 Instruments And Techniques

Scientific paper

We investigate an Omega-band event that took place above northern Scandinavia around 02:00 - 02:30 UT on 9.3.1999. The Omega-band event occured in the recovery phase of a moderate substorm. In the first part of the study we compare ground- and space-based estimates of the ionospheric Hall and Pedersen conductances during the Omega-band event. Ground-based measurements offer good spatial and temporal resolution, but their spatial extent is often limited. Space based observation are complementary, offering good coverage but limited resolution. The ground-based conductance estimates are derived with two different methods: (i) from measurements of cosmic radio noise absorption with the method developed by Senior et al. (2007) and (ii) by combining riometer data with 557.7 nm ASC data with the method by Kosch et al. (2001). The absorption measurements are done with the Kilpisjärvi IRIS imaging riometer. The space- based conductance estimates are derived from ultraviolet images taken by the UVI instrument on board the POLAR satellite. The process of estimating ionospheric conductances from the intensity of the auroral ultraviolet emission is descibed by Lummerzheim et al. (1991). We compare these three conductance estimates for the Omega-band event by taking temporal and spatial averages of the higher resolution ground-based data. Our data set of 12 time frames (with 10 grid points each) shows the tendency of space- based conductances to be 15-40% smaller than ground-based conductance estimates. In the second part of the study we examine the electrodynamic structure of the Omega-band. The ionospheric electric field of Omega-bands has mostly been studied with coherent scatter radars, which may have trouble in resolving small electric fields, such as those that are present in the highly conductive luminous "tongues" of the Omega-band. We calculate the ionospheric electric field from the conductance estimates and ground magnetic measurements with the method developed by Vanhamäki and Amm (2007). Both the riometer- and UVI-based conductance estimates should have their best accuracy in the luminous "tongues", where electron precipitation is intense and conductances are high. High resolution riometer and magnetometer measurements allow us to asses the electric field structure of the whole Omega-band, including the luminous tongues, thus completing the previous studies.

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