Other
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jgra..11303312n&link_type=abstract
Journal of Geophysical Research, Volume 113, Issue A3, CiteID A03312
Other
1
Ionosphere: Polar Cap Ionosphere, Ionosphere: Topside Ionosphere, Ionosphere: Particle Acceleration, Ionosphere: Electric Fields (2712), Ionosphere: Plasma Temperature And Density
Scientific paper
Using the mass conservation equation, the parallel electron upflow velocity normalized by the base velocity in the polar cap region of the topside ionosphere is derived as a function of electron density and neutral species densities. The normalized parallel velocity profiles are evaluated using ISIS 2 electron density observations and neutral species density profiles from the MSIS model. From the cases analyzed, the derived velocity profiles show a similar trend of (a) a region of slow acceleration below an altitude of ~500 km, (b) a region of fast acceleration (~500 km-1100 km), and (c) another region of weak or no acceleration (>~1100 km). A simple analytical function is proposed to empirically describe the normalized parallel velocity profile. The parameters in the function have been determined by a multivariate least squares fit of calculated profiles to the analytical expression. These parameters define the magnitude and the height of maximum acceleration. For the cases studied the maximum acceleration height occurred in the range of 731-908 km. The parallel velocity can increase by a factor of up to 6 within the acceleration region. The results from the cases studied suggest that the chosen analytical function suitably describes the normalized parallel electron velocity in the high-latitude topside ionosphere. Furthermore, the acceleration mechanisms have been investigated using the electron momentum equation. On the basis of an existing model of the electron temperature, our results suggest that the enhanced pressure gradient force may be the main driver of the observed acceleration in the electron upflow.
Huang Xueqin
Nsumei Patrick A.
Reinisch Bodo. W.
Song Paul
Tu Jiannan
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