Energy deposition by precipitating electrons and how it affects ionospheric electrodynamics
Techniques: Multi-spectral global imaging is a strong tool to derive information about the energy characteristics of precipitating electrons and protons. We have shown that the combined measurements of ultraviolet emissions and X-rays from space can be used to derive electron spectra in the energy range from 100 eV to 100 keV on a global scale. We have also shown that the techniques give results that are consistent with insitu particle measurements from low-altitude spacecraft.
Main content
Energy deposition from electron precipitation as a function of geomagnetic indices: We have also examined how the hemispherical energy deposition (0.1-100 keV) relates to the geomagnetic indices AL and AE and presented simple expressions that can be used when global imaging is not available.
N. Ostgaard, R. R. Vondrak, J. W. Gjerloev, G. A. Germany, A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms. J. Geophys. Res., Vol. 107, NO. A9, 1233, doi: 10.1029/2001JA002003, 2002.
Electron precipitation and ionospheric conductances:
From remote sensing of UV and X-ray emissions by the UVI and PIXIE cameras onboard the Polar satellite, we derive global maps of the precipitating electron energy spectra from less than 1 keV to 100 keV. Based on the electron spectra, we infer height profiles of the resulting ionization. Photo ionization is also included in these calculations. We then generate instantaneous global maps of the Hall and Pedersen conductances. This technique allows us to study the time development of the conductances during geomagnetic substorms.
A. Aksnes, J. Stadsnes, J. Bjordal, N. Østgaard, R. R. Vondrak, D. L. Detrick, T. J. Rosenberg, G. A. Germany, and D. Chenette, Instantaneous ionospheric global conductance maps during an isolated substorm. Annales Geophysicae, 20, 1181, 2002.
Remote sensing of UV emissions gives good coverage of the precipitating electrons in the energy range of a few keV, responsible for the Pedersen conductance. X-ray measurements are needed to capture the high-energy tail of the energetic electrons from some tens of keV and up to 100 keV affecting the Hall conductance. The PIXIE X-ray camera on the Polar satellite is the only instrument providing global information about the energetic electron precipitation. Instantaneous global conductance maps derived with and without the inclusion of PIXIE X-ray data have been implemented in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to study the effects of energetic electrons on the ionospheric electrodynamics. This includes ionospheric conductances, the ionospheric electric field, the atmospheric Joule heating, and the auroral energy flux.
A. Aksnes, J. Stadsnes, G. Lu, N. Østgaard, R. R. Vondrak, D. L. Detrick, T. J. Rosenberg, G. A. Germany, and M. Schulz, Effects of energetic electrons on the electrodynamics in the ionosphere. Annales Geophysicae, 22, 475, 2004.
The method of characteristics is a ground-based technique to derive the ionospheric conductances, using electric field measurements and ground magnetometer data. We have derived and compared conductances above Northern Scandinavia using method of characteristics (the MIRACLE network) and remote sensing of UV and X-ray emissions (UVI and PIXIE on the Polar satellite).
A. Aksnes, O. Amm, J. Stadsnes, N. Østgaard, G. A. Germany, R. R. Vondrak, and I. Sillanpaa, Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: A comparison. Accepted for publication in Annales Geophysicae, 2004.
Another study the group in Bergen has participated in is the analysis of mesoscale ionospheric electrodynamics of omega bands. An omega band is an auroral phenomena typically occurring on the morning side diffuse aurora in the recovery phase of substorms. Auroral omega bands are periodic, wave-like undulations of the poleward boundary of the aurora, and the name omega is due to the dark areas between the auroral tongues, which resemble the form of the inverted capital Greek letter. We use ground-based electromagnetic data from the MIRACLE and BEAR networks and satellite optical observations from the UVI and PIXIE instruments on the Polar satellite to study the ionospheric electrodynamics during an omega band event over Northern Scandinavia.
0. Amm, A. Aksnes, J. Stadsnes, N. Østgaard, R. R. Vondrak, G. A. Germany, G. Lu, and A. Viljanen, Mesoscale ionospheric electrodynamics of omega bands determined from ground-based electronmagnetic and satellite optical observation. Accepted for publication in Annales Geophysicae, 2004.
0. Amm, A. Aksnes, J. Stadsnes, N. Østgaard, R. R. Vondrak, G. A. Germany, and I. Sillanpaa, Observations and analysis of ionospheric electrodynamics during a substorm recovery phase using the MIRACLE network. Proc. Seventh International Conf. on Substorms (ICS-7), Levi, Finland, March 21-27, 2004, Finnish Meterological Institute report 2004:5, p. 87-94, 2004.
