We developed a one-dimensional photochemical model for the dayside ionosphere of Titan for calculating the density profiles of negative ions under steady-state photochemical equilibrium condition. We concentrated on the T40 flyby of the Cassini orbiter and used the in situ measurements from instruments on board Cassini as input to the model. Using the latest available reaction rate coefficients and dissociative electron attachment cross sections, the densities of 10 anions are calculated. Our study shows CN− as the dominant anion, followed by C3N−, which agrees with the results of previous calculations. We suggest that H− could be an important anion in Titan’s ionosphere and is the second most abundant anion at altitudes greater than 1200 km. The main production channel of the major ion CN− is the reaction of H− with HCN. The H− also play a major role in the production of anions C2H−, C6H−, and OH−. We present a comparison of the calculated ion density profiles with the relative density profiles derived using recently reported Cassini CAPS/ELS observations.
Global or planet encircling dust storms, a prominent phenomenon on Mars, are known to cause dynamic changes in atmospheric parameters such as neutral densities, temperature and pressure around most of the planet (Smith et al., 2002). During the storm event, the dust particles are elevated to greater heights and can remain at these altitudes for several months (Clancy et al., 2010). These particles absorb solar radiation, warm the lower atmosphere and lead to the inflation of the atmosphere. Due to the coupling between the lower and upper atmospheric regions, the impact of storm events is seen even in the upper atmospheric regions including the thermosphere, ionosphere, exosphere, and magnetosphere where dust particles do not physically reach (
We present a Monte Carlo model for degradation of 1-10,000 eV electrons in an atmosphere of methane. The electron impact cross sections for CH 4 are compiled and analytical representations of these cross sections are used as input to the model."Yield spectra", which provides information about the number of inelastic events that have taken place in each energy bin, is used to calculate the yield (or population) of various inelastic processes. The numerical yield spectra, obtained from the Monte Carlo simulations, is represented analytically, thus generating the Analytical Yield Spectra (AYS). AYS is employed to obtain the mean energy per ion pair and efficiencies of various inelastic processes. Mean energy per ion pair for neutral CH 4 is found to be 26 (27.8) eV at 10 (0.1) keV. Efficiency calculation showed that ionization is the dominant process at energies >50 eV, for which more than 50% of the incident electron energy is used. Above 25 eV, dissociation has an efficiency of ∼27%. Below 10 eV, vibrational excitation dominates. Contribution of emission is around 1.2% at 10 keV. Efficiency of attachment process is ∼0.1% at 8 eV and efficiency falls down to negligibly small values at energies greater than 15 eV. The efficiencies can be used to calculate volume production rate in planetary atmospheres by folding with electron production rate and integrating over energy.
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