Electron impact ionization: A new parameterization for 100 eV to 1 MeV electrons

Fang, Xiaohua; Randall, C. E.; Lummerzheim, D.; Solomon, Stanley C.; Mills, Michael J.; Marsh, Daniel R.; Jackman, Charles H.; Wang, Wenbin; Lu, G.

doi:10.1029/2008ja013384

Cited by 95 publications

(139 citation statements)

References 15 publications

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“…The influence of 900 eV particles on the neutral density at 400 km is almost negligible. When the particles are more energetic, they penetrate deeper into the atmosphere [ Roble and Ridley , ; Millward et al , ; Fang et al , ] and increase the Joule heating at lower altitudes. If the Joule heating energy deposition were the same, then the neutral gas heating rate would be lower, since the heating rate is the energy deposition rate divided by the mass density, which is larger at lower altitudes.…”

Section: Resultsmentioning

confidence: 99%

Theoretical study: Influence of different energy sources on the cusp neutral density enhancement

et al. 2013

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[1] Simulations with the Global Ionosphere-Thermosphere Model (GITM) show that both Poynting flux and soft electron precipitation are important in producing neutral density enhancements near 400 km altitude in the cusp that have been observed by the Challenging Minisatellite Payload (CHAMP) satellite. Imposing a Poynting flux of 75 mW/m 2 in the cusp within the model increases the neutral density by 34%. The direct heating from 100 eV, 2 mW/m 2 soft electron precipitation produces only a 5% neutral density enhancement at 400 km. However, the associated enhanced ionization in the F-region from the electron precipitation leads to a neutral density enhancement of 24% through increased Joule heating. Thus, the net effect of the soft electron is close to 29%, and the combined influence of Poynting flux and soft particle precipitation causes a more than 50% increase in neutral density at 400 km, which is consistent with CHAMP observations in extreme cases. The effect of electron precipitation on the neutral density at 400 km decreases sharply with increasing characteristic energy such that 900 eV electrons have little effect on neutral density. Finally, the impact of 2 keV, 0.3 mW/m 2 proton precipitation on the neutral density is negligible due to a lowering of the altitude of Joule heating.

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Section: Resultsmentioning

confidence: 99%

Theoretical study: Influence of different energy sources on the cusp neutral density enhancement

et al. 2013

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“…Second, as seen in Figure , protons with a lower energy have a smaller W value and thus a higher ionizing efficiency, which is understandable considering the increased efficiency of charge exchange‐induced ionization at low energies (see Basu et al [] for the comparison of collisional cross sections). In contrast, lower‐energetic electrons have a lower ionizing efficiency [e.g., Fang et al , ; Simon Wedlund et al , ]. Combining these two reasons offers a coherent view of how the secondary‐to‐primary ratio differs when comparing altitude‐integrated ionization and peak ionization.…”

Section: Coupled Monte Carlo and Multistream Modelmentioning

confidence: 99%

Proton impact ionization and a fast calculation method

2013

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[1] We present a coupled Monte Carlo and multistream model simulating primary ionization and secondary electron ionization, respectively, from energetic proton precipitation in the Earth's upper atmosphere. Good agreement is obtained with previous model results. It is found that while secondary electrons make a negligible contribution to ionization from low-energy (Ä10 keV) auroral proton precipitation, their importance increases with increasing incident proton energy, confirming earlier findings. It becomes significant or even comparable to primary ionization from protons and generated hydrogen atoms in charge-changing collisions. Our calculations of the mean energy loss per ion pair production show a nearly monotonic increase with incident proton energy, ranging from about 22 eV to 33 eV when incident energy increases from 100 eV to 1 MeV. To facilitate a fast calculation in large-scale computations, we develop a parameterization for total (primary plus secondary) ionization from monoenergetic proton precipitation. This is obtained by fitting to a large set of numerical results from the coupled model. The quick method applies to a wide energy range of 100 eV to 1 MeV for incident monoenergetic protons, and its validity has been extensively tested under a variety of background atmospheric conditions. Our new parameterization can be used to rapidly calculate the ionization altitude profile from precipitating protons with any spectral distributions without any significant compromise in accuracy. By considering branching ratios of ionized atmospheric species, the fast calculation method is thus useful for self-consistently including proton impact effects in large community models.Citation: Fang, X., D. Lummerzheim, and C. H. Jackman (2013), Proton impact ionization and a fast calculation method,

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“…There have been several parameterizations for calculating electron impact ionization rates, e.g., Lazarev [1967], Roble and Ridley [1987], Frahm et al [1997], Fang et al [2008], and Fang et al [2010. Large-scale global circulation models (GCMs) have to rely on these empirical models to quickly and self-consistently calculate and incorporate the particle impact ionization.…”

Section: Introductionmentioning

confidence: 99%

Ionization due to electron and proton precipitation during the August 2011 storm

Huang

et al. 2014

JGR Space Physics

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The parameterizations of monoenergetic particle impact ionization in Fang et al. (2010) (Fang2010) and Fang et al. (2013 are applied to the complex energy spectra measured by DMSP F16 satellite to calculate the ionization rates from electron and ion precipitations for a Northern Hemisphere pass from 0030 UT to 0106 UT on 6 August 2011. Clear enhancement of electron flux is found in the polar cap. The mean electron energy in the polar cap is mostly above 100 eV, while the mean energy in the auroral zone is typically above 1 keV. At the same time, F16 captures a strong Poynting flux enhancement in the polar cap, which is comparable to those in the auroral zone. The particle impact ionization rates using Fang2010 and Fang2013 parameterizations show clear enhancement at F region altitudes mainly due to the low-energy precipitating electrons, peaking probably in the cusp but also showing enhanced levels throughout most of the polar cap region. The general circulation models (GCMs), National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model, and Global Ionosphere-Thermosphere Model, using their default empirical formulations of particle impact ionization, do not capture the observed features shown in the total particle ionization rate applying the Fang2010 and Fang2013 parameterizations to DMSP measurements. The difference between GCM simulations and Fang2010 and Fang2013 applied to DMSP data is due to the difference of both the inputs to the models and the parameterization of the ionization rates.

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Electron impact ionization: A new parameterization for 100 eV to 1 MeV electrons

Cited by 95 publications

References 15 publications

Theoretical study: Influence of different energy sources on the cusp neutral density enhancement

Theoretical study: Influence of different energy sources on the cusp neutral density enhancement

Proton impact ionization and a fast calculation method

Ionization due to electron and proton precipitation during the August 2011 storm

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