Journal article
Inner magnetospheric electron temperature and spacecraft potential estimated from concurrent Polar upper hybrid frequency and relative potential measurements
Journal of geophysical research. Space physics, Vol.119(10), pp.8046-8062
10/2014
DOI: 10.1002/2014JA019852
Abstract
Direct measurement of low <1eV electron temperature is difficult to make in the Earth's inner magnetosphere for electron densities (N-e)<3x10(2) cm(-3). We compute these quantities by solving current balance equations in low-density regions. Concurrent measurements from the Polar spacecraft of the relative potential (V-S-V-P), between the spacecraft body and the electric field probe, and the electron density (N-e), derived from upper hybrid frequency (f(UHR)), were used in the current balance equations to solve for the electron temperature (T-e), V-s, and V-p. Where V-P is the probe potential and V-S is the spacecraft potential relative to the nearby plasma. The assumption that the bulk plasma electrons are Maxwellian is used in the computations. Our data set covered 1.5years of measurements when f(UHR) was detectable (L<10). The following averaged T-e versus L relation for 3<L<5 was obtained: T-e=0.58+0.49(L-3)eV. This expression is in reasonable agreement with extrapolations of ionospheric T-e measurements by Akebono at lower altitudes. However, the solution is sensitive to the photoemission coefficients, substituting those of Scudder et al. (2000) with those of Escoubet et al. (1997), the T-e curve shifted upward by similar to 1eV. Also, the solution is sensitive to measurement error of V-S-V-P, applying a voltage shift of 0.1 and 0.2V to V-S-V-P, the relative median error for our data set was computed to be 0.27 and 1.04, respectively. We believe that our T-e values computed outside the plasmasphere are unrealistically low. We conclude that this method shows promise inside the plasmasphere but should be used with caution. We also quantified the N-e versus V-S-V-P relationship. The running median N-e versus V-S-V-P curve shows no significant variation over the 1.5year period of the data set, suggesting that the photoemission coefficients did not change significantly over this time span. The Scudder et al. (2000) N-e model, based on only one Polar orbit, is in reasonable agreement (within a factor of 2) with our results.
Details
- Title: Subtitle
- Inner magnetospheric electron temperature and spacecraft potential estimated from concurrent Polar upper hybrid frequency and relative potential measurements
- Creators
- S. A. Boardsen - University of Maryland, BaltimoreM. L. Adrian - HeliophysicsR. Pfaff - HeliophysicsJ. D. Menietti - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.119(10), pp.8046-8062
- Publisher
- Amer Geophysical Union
- DOI
- 10.1002/2014JA019852
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 17
- Language
- English
- Date published
- 10/2014
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984627245402771
Metrics
1 Record Views