Photoelectron flux buildup in the plasmasphere

Mantas, G. P.; Carlson, H. C.; Wickwar, Vincent B

doi:10.1029/ja083ia01p00001

Cited by 41 publications

(22 citation statements)

References 49 publications

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“…Nevertheless, the fact that it is possible for photoelectrons to traverse the long distances through the magnetosphere without significant degradation is important. This finding of minimal degradation in the magnetosphere agrees with the finding of Mantas et al [1978] who estimated that pitch angle trapping increases the equilibrium photoelectron flux in the magnetosphere by about 10%. However, if the mirror altitude of the trapped photoelectrons were above the satellite altitude, pitch angle trapping would actually lower the flux from the conjugate ionosphere.…”

Section: Resultssupporting

confidence: 91%

Measured and modeled backscatter of ionospheric photoelectron fluxes

Richards

Peterson

2008

J. Geophys. Res.

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[1] This paper examines the backscatter of ionospheric photoelectrons from the thermosphere using photoelectron measurements made on closed field lines in the magnetosphere from 1997 to 2004. The satellite made simultaneous measurements of both the precipitating photoelectrons from the sunlit conjugate hemisphere and the backscattered electrons from the dark thermosphere. The backscatter ratios of the observed fluxes are in very good agreement with photoelectron model calculations for energies ranging from a few eV to several hundred eV and for different levels of solar activity. The backscattered electron flux consists of a direct elastic backscatter component that is a weak function of energy and a much stronger cascade component that greatly increases with decreasing electron energy so that the backscatter ratio ranges from 0.2 at high energies to greater than one at low energies. Although the photoelectron fluxes can vary by up to an order of magnitude over the solar cycle, the backscatter ratios show only a small variation above 20 eV. There can be a factor of 2 or more variability in the backscatter ratios for energies below 20 eV due to thermal electron Coulomb interactions. The calculations show that 55-60% of the precipitating flux energy is backscattered from the thermosphere back along the field line to the conjugate hemisphere. The model-data comparisons show that photoelectrons are able to travel the long journey from the sunlit hemisphere to the satellite without significant degradation indicating that pitch angle scattering and trapping of photoelectrons in the magnetosphere may be small.

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Section: Resultssupporting

confidence: 91%

Measured and modeled backscatter of ionospheric photoelectron fluxes

Richards

Peterson

2008

J. Geophys. Res.

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“…Particularly below 250 km altitude, T e is maintained by photoelectron heating [ Roble , 1975]. Furthermore, the interaction between high‐energy photoelectrons and thermal electrons is well accepted as the heat source of the plasmasphere [ Mantas et al , 1978; Narasinga Rao and Maier , 1970]. Since the pitch angle of the photoelectron varies with the angle between the direction of the incident photon and the magnetic field line, the pitch angle has local time and seasonal dependence.…”

Section: Discussionmentioning

confidence: 99%

Predawn ionospheric heating observed by Hinotori satellite

et al. 2010

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[1] Predawn ionospheric temperature has been known to increase with conjugate sunrise. This paper presents the onset time of predawn ionospheric heating and heating rate at around 600 km height globally using Hinotori electron temperature data for magnetically quiet (Kp < 4 and Dst > À50 nT) medium to high solar activity conditions. The analysis of the data shows that the onset of predawn ionospheric heating occurs at nearly the same solar zenith angle (SZA) of the conjugate point at low latitudes where the geomagnetic field line is shorter than about 5000 km. However, at higher latitudes with longer field lines, the conjugate SZA decreases with increasing field line length. In addition, the heating rate decreases with increasing field line length until the field line becomes about 5000 km long, and the rate remains nearly constant for longer field lines. The conjugate SZA increases with increasing solar activity (F 10.7 ) until F 10.7 reaches about 200, and the conjugate SZA remains nearly constant for higher F 10.7 . The observations indicate that the photoelectron flux causing predawn ionospheric heating is attenuated by scattering in the high-altitude (>600 km) ionosphere and plasmasphere.

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“…Photoelectrons escaping from one ionosphere and traveling to the conjugate ionosphere through the plasmasphere constitute a major nonlocal heat source for the thermal electrons in the plasmasphere. The photoelectrons heat the thermal electrons through Coulomb collisions, magnetic trapping due to pitch angle diffusion, and backscattering from the conjugate ionosphere before being thermalized [Rao and Maier, 1970;Lejeune and Wormser, 1976;Mantas et al, 1978;Khazanov et al, 1993;Khazanov and Liemohn, 1995]; these processes can increase the plasmaspheric flux by about 5%, 20%, and 40%, respectively [Mantas et al, 1978;Newberry et al, 1989]. In the photoelectron code, backscattering is included self-consistently, and pitch angle diffusion is taken care of by assuming that a fraction of the photoelectrons is trapped and that all the energy of the trapped flux is deposited in the plasmasphere.…”

Section: Model Calculationsmentioning

confidence: 99%

Plasmasphere electron temperature profiles and the effects of photoelectron trapping and an equatorial high‐altitude heat source

Balan¹,

Oyama²,

Bailey³

et al. 1996

J. Geophys. Res.

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The electron temperature Te in the Earth's plasmasphere up to 10,000 km altitude, has been measured routinely by a thermal electron energy distribution instrument on board the EXOS D satellite. The measurements made during the years 1989–1995 have been analyzed to obtain altitude (1000–8000 km) profiles of Te for magnetic latitudes 0°–40°N at different times of the day. The profiles are compared with those computed by the Sheffield University plasmasphere‐ionosphere model, modified to include nonlocal heating due to trapped photoelectrons and an equatorial high‐altitude heat source. The photoelectrons are trapped at altitudes above 600 km, and the high‐altitude heat source is applied as energy input along the magnetic field lines with apex altitude greater than 600 km between ±10° magnetic latitude. The results for 8000 km altitude show that the modeled values of Te computed without photoelectron trapping and the high‐altitude heat source are much less than the mean measured values, 3700 K compared with 6500 K. Depending upon altitude and latitude, a photoelectron trapping of up to 100% is required to raise the modeled electron temperatures to the mean measured values. However, photoelectron trapping alone cannot account for the observed latitude variation of Te, which depends on altitude. Model calculations carried out with 50% photoelectron trapping and an altitude and local time‐dependent high‐altitude heat source reproduce the measurements, including the latitude variation; the heat source required for nighttime is about one fourth of that required for daytime. An equatorial high‐altitude heat source appears to be the only mechanism that can account for the measured values of Te; values in excess of 12,000 K have been measured. There are some quantitative differences between the measured and modeled temperatures at night in the lower plasmasphere (<2500 km), which could be caused, in whole or in part, by the inaccuracies of the nighttime measurements due to the low plasma densities.

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Photoelectron flux buildup in the plasmasphere

Cited by 41 publications

References 49 publications

Measured and modeled backscatter of ionospheric photoelectron fluxes

Measured and modeled backscatter of ionospheric photoelectron fluxes

Predawn ionospheric heating observed by Hinotori satellite

Plasmasphere electron temperature profiles and the effects of photoelectron trapping and an equatorial high‐altitude heat source

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