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Numerical interpretation of high-altitude photoelectron observations |
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| Authors: | Michael W Liemohn RA Frahm Y Ma R Lundin AF Nagy J Bell D Mitchell M Holmström M Yamauchi S McKenna-Lawler JR Scherrer AJ Coates DO Kataria H Koskinen T Säles W Schmidt D Williams CC Curtis BR Sandel M Carter A Fedorov S Orsini M Maggi P Bochsler J Woch K Asamura |
| Institution: | a Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA b Southwest Research Institute, San Antonio, TX, USA c Swedish Institute of Space Physics, Box 812, S-98 128, Kiruna, Sweden d Space Sciences Laboratory, University of California, Berkeley, CA, USA e Space Technology Ireland, National University of Ireland, Maynooth, Co. Kildare, Ireland f Southwest Research Institute, San Antonio, TX 7228-0510, USA g Mullard Space Science Laboratory, University College London, Surrey RH5 6NT, UK h Finnish Meteorological Institute, Box 503, FIN-00101 Helsinki, Finland i Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723-6099, USA j University of Arizona, Tucson, AZ 85721, USA k Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK l Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France m Istituto di Fisica dello Spazio Interplanetari, I-00133 Rome, Italy n Physikalisches Institut, University of Bern, CH-3012 Bern, Switzerland o Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany p Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamichara, Japan q Technical University of Braunschweig, Hans-Sommer-Strasse 66, D-38106 Braunschweig, Germany |
| Abstract: | The Electron Spectrometer (ELS) instrument of the ASPERA-3 package on the Mars Express satellite has recorded photoelectron energy spectra up to apoapsis (∼10,000 km altitude). The characteristic photoelectron shape of the spectrum is sometimes seen well above the ionosphere in the evening sector across a wide range of near-equatorial latitudes. Two numerical models are used to analyze the characteristics of these high-altitude photoelectrons. The first is a global, multi-species MHD code that produces a 3-D representation of the magnetic field and bulk plasma parameters around Mars. It is used here to examine the possibility of magnetic connectivity between the high-altitude flanks of the martian ionosheath and the subsolar ionosphere. It is shown that some field lines in this region are draped interplanetary magnetic lines while others are open field lines (connected to both the IMF and the crustal magnetic field sources). The second model is a kinetic electron transport model that calculates the electron velocity space distribution along a selected, non-uniform, magnetic field line. It is used here to simulate the high-altitude ELS measurements. It is shown that the photoelectrons are essentially confined to the source cone, as governed by magnetic field inhomogeneity along the field line. Reasonable agreement is shown between the data and the model results, and a method is demonstrated for inferring properties of the local and photoelectron source region magnetic field from the ELS measurements. Specifically, the number of sectors in which photoelectrons are measured is a function of the magnetic field intensity ratio and the field's angle with respect to the detector plane. In addition, the sector of the photoelectron flux peak is a function of the magnetic field azimuthal angle in the detector plane. |
| Keywords: | Mars Magnetospheres Ionospheres Magnetic fields |
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