Monte Carlo model of electron energy degradation in a CO<sub>2</sub> atmosphere

Bhardwaj, Anil; Jain, Sonal

doi:10.1029/2009ja014298

Cited by 40 publications

(75 citation statements)

References 84 publications

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“…These processes are parameterized by the primary and secondary ionization rates, respectively, with the ratio of the latter to the former being frequently termed as ionization efficiency (Richards & Torr 1988). The calculation of the primary ionization rate is straightforward with the aid of the classical Beer-Lambert law, whereas the calculation of the secondary ionization rate, which requires either the implementation of the Monte Carlo algorithm (e.g., Bhardwaj & Jain 2009) or the multi-stream solution to the Boltzmann equation (e.g., Wedlund et al 2011), is far more involved.…”

Section: Introductionmentioning

confidence: 99%

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cui

et al. 2018

ApJL

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Combining the Mars Atmosphere and Volatile Evolution measurements of neutral atmospheric density, solar EUV/X-ray flux, and differential photoelectron intensity made during 240 nominal orbits, we calculate the ionization efficiency, defined as the ratio of the secondary (photoelectron impact) ionization rate to the primary (photon impact) ionization rate, in the dayside Martian upper atmosphere under a range of solar illumination conditions. Both the CO 2 and O ionization efficiencies tend to be constant from 160km up to 250km, with respective median values of 0.19±0.03 and 0.27±0.04. These values are useful for fast calculation of the ionization rate in the dayside Martian upper atmosphere, without the need to construct photoelectron transport models. No substantial diurnal and solar cycle variations can be identified, except for a marginal trend of reduced ionization efficiency approaching the terminator. These observations are favorably interpreted by a simple scenario with ionization efficiencies, as a first approximation, determined by a comparison between relevant cross sections. Our analysis further reveals a connection between regions with strong crustal magnetic fields and regions with high ionization efficiencies, which are likely indicative of more efficient vertical transport of photoelectrons near magnetic anomalies.

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Section: Introductionmentioning

confidence: 99%

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cui

et al. 2018

ApJL

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“…Comparisons of calculations using this approximation with more sophisticated electron transport models have shown good agreement in the altitude region where UV dayglow emissions are produced (Jain & Bhardwaj, ; Simon et al, ). Given the computation time constrains associated with the use of a GCM, we have chosen to calculate the energy degradation of the photoelectrons using the Analytical Yield Scheme (AYS) technique (e.g., Bhardwaj & Jain, ). This technique provides a fast expression based on rigorous Monte Carlo calculations, producing a good compromise between accuracy and calculation speed, ideal for implementation in a GCM.…”

Section: Methodsmentioning

confidence: 99%

“…In particular, the photoelectron energy flux at the altitude layer Z and energy E is calculated from the photoelectron production rate using expression (4) in Jain and Bhardwaj ():

ϕ false(Z, E false) = \int_{W_{L}}^{200} \frac{P_{e} false(E, Z false) U false(E, E_{0} false)}{\sum_{l} n_{l} false(Z false) σ_{lT} false(E false)} normald E_{0}

where σ l T ( E ) is the total inelastic cross section for gas l (cm 2 ), n l ( Z ) is its density (cm −3 ), and U ( E , E 0 ) is the AYS (eV −1 ). See more details about the significance of the AYS in Bhardwaj and Jain (), Jain and Bhardwaj (, ), and Bhardwaj and Jain (). For the AYS of CO 2 we use a modified version of expression (5) in Jain and Bhardwaj (), due to a mistake in the original text:

U false(E, E_{0} false) = A_{1} E_{k}^{s} + A_{2} ((), E_{k} false/ ε^{1.5}) + \frac{E_{0} B_{0} e^{- x} false/ B_{1}}{{false(1 + e^{x} false)}^{2}}

where the values of the parameters are the same as in Jain and Bhardwaj ().…”

Section: Methodsmentioning

confidence: 99%

UV Dayglow Variability on Mars: Simulation With a Global Climate Model and Comparison With SPICAM/MEx Data

et al. 2018

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A model able to simulate the CO Cameron bands and the CO 2+ UV doublet, two of the most prominent UV emissions in the Martian dayside, has been incorporated into a Mars global climate model. The model self‐consistently quantifies the effects of atmospheric variability on the simulated dayglow for the first time. Comparison of the modeled peak intensities with Mars Express (MEx) SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) observations confirms previous suggestions that electron impact cross sections on CO2 and CO need to be reduced. The peak altitudes are well predicted by the model, except for the period of MY28 characterized by the presence of a global dust storm. Global maps of the simulated emission systems have been produced, showing a seasonal variability of the peak intensities dominated by the eccentricity of the Martian orbit. A significant contribution of the CO electron impact excitation to the Cameron bands is found, with variability linked to that of the CO abundance. This is in disagreement with previous theoretical models, due to the larger CO abundance predicted by our model. In addition, the contribution of this process increases with altitude, indicating that care should be taken when trying to derive temperatures from the scale height of this emission. The analysis of the geographical variability of the predicted intensities reflects the predicted density variability. In particular, a longitudinal variability dominated by a wave‐3 pattern is obtained both in the predicted density and in the predicted peak altitudes.

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“…An additional process of neutral dissociation (N+N) is considered in our calculations, with the cross-section data taken from Cosby [1993]. The cross sections for electron impact dissociative ionization of CO 2 are based on the work by Tian and Vidal [1998a] and Bhardwaj and Jain [2009]. The CO 2 vibrational excitation cross sections are adopted from the compilations of Itikawa [2002] and Kochem et al [1985].…”

Section: Discussionmentioning

confidence: 99%

“…The CO 2 vibrational excitation cross sections are adopted from the compilations of Itikawa [2002] and Kochem et al [1985]. Calculations of electronic excitation of CO 2 are based on the empirical expressions of Jackman et al [1977], with the updated parameters given by Bhardwaj and Jain [2009]. Cross sections for CO electronic and vibrational excitations are based on the results of Jackman et al [1977], Brunger and Buckman [2002] and Poparić et al [2006].…”

Section: Discussionmentioning

confidence: 99%

Suprathermal electron spectra in the Venus ionosphere

et al. 2011

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[1] In this study, a multistream kinetic model is used to derive the suprathermal electron intensity in the Venus ionosphere, to be compared with the observations made by the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) instrument onboard Venus Express (VEx) on 18 May 2006. Input parameters of the model are chosen to be consistent with the detailed ephemeris information. We consider two cases for the magnetic field line configuration. The first assumes vertical magnetic field lines, while in the second the configuration is consistent with the VEx Magnetometer (MAG) measurements for that particular orbit. The model calculations suggest that the energy spectrum of suprathermal electrons not only depends on the local photoelectron production but is also strongly influenced by transport as well as energy degradation. We confirm the postulation of Coates et al. (2008) (2008). The model results indicate that the condition of local equilibrium is satisfied for suprathermal electrons below ∼155 km on Venus. However, transport becomes effective at higher altitudes, significantly altering the secondary electron production rate and leading to strongly anisotropic suprathermal electron flow. For the case with the MAG-derived, slanted magnetic field configuration, we make a data-model comparison in terms of both the absolute magnitude of the suprathermal electron intensity and the appearance of spectral peaks. The comparison suggests that the actual magnetic field lines are probably inclined more vertically than a simple extrapolation from the MAG measurements.

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Monte Carlo model of electron energy degradation in a CO₂ atmosphere

Cited by 40 publications

References 84 publications

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Ionization Efficiency in the Dayside Martian Upper Atmosphere

UV Dayglow Variability on Mars: Simulation With a Global Climate Model and Comparison With SPICAM/MEx Data

Suprathermal electron spectra in the Venus ionosphere

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Monte Carlo model of electron energy degradation in a CO2 atmosphere

Cited by 40 publications

References 84 publications

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Ionization Efficiency in the Dayside Martian Upper Atmosphere

UV Dayglow Variability on Mars: Simulation With a Global Climate Model and Comparison With SPICAM/MEx Data

Suprathermal electron spectra in the Venus ionosphere

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Monte Carlo model of electron energy degradation in a CO₂ atmosphere