Dust charging and electrical conductivity in the day and nighttime atmosphere of Mars

Abstract

[1] Understanding aerosol charging and atmospheric conductivity are necessary in describing the global electric circuit, the aerosol coagulation rate, aerosol-cloud interaction and their subsequent affect on the climate. The importance of aerosol charging for the conductivity variations of the lower Martian atmosphere during both day and night is calculated. Galactic cosmic rays are the dominant ionizing agent in the lower atmosphere, producing molecular ions and ion clusters. During the nighttime these ion clusters get attached to the aerosols and charging occurs. Solar UV photons are an additional ionizing agent during the day-time. Only solar photons of energy less than 6 eV reach the surface of Mars as those with energies greater than 6 eV are absorbed by atmospheric molecules before they reach the lower atmosphere. Those photons which do reach the lower atmosphere ionize the aerosols as the ionization potential of most of the aerosols is less than 6 eV and produce electrons. Aerosols become charged by the attachment of ions and electrons during the day-time. The ion-aerosol and electron-aerosol attachment coefficients, as well as the ion-ion and ion-electron recombination rates are calculated. The charge distribution of aerosols is obtained by the simultaneous solution of the ion-aerosol charge balance equations. Both the steady state and time dependent concentration of charged aerosols are calculated. More than 60% of the ions and 95% of the electrons get attached to the aerosols. There are more negatively charged aerosols in steady state due to the presence of highly mobile electrons during the day-time. The presence of electrons increases the conductivity during the day time. The day-time results are compared with the nighttime results.

In situ detection of electrified aerosols in the upper troposphere and stratosphere

“…Bigger particles (radius > 3.3 µm) show a flatter charge distribution and carry up to ±10 electronic charges. The ion-aerosol attachment coefficients increase with the particle size, and therefore larger particles carry more charges compared to the smaller particles (Tripathi et al, 2008;Michael et al, 2008Michael et al, , 2009. Similar results were observed at other altitudes (not shown here).…”

Intensity of nightside MARSIS AIS surface reflections and implications for low‐altitude ionospheric densities

“…This might be consistent with the results of Haider et al [], who reported that during a dust storm a decrease of the ion concentrations resulting from ionization by galactic cosmic rays may appear in the lower region of the Martian ionosphere. This result is consistent with the study of aerosol charging in the Martian atmosphere by Michael et al [], who showed that both ion and electron densities resulting from ionization by galactic cosmic rays are decreased close to the surface (below about 40 km altitude) when they become attached to aerosols during dust storms. This would, in turn, result in lower attenuation of the sounding signal, and therefore larger ground trace intensities.…”

A study of the possibility of sprites in the atmospheres of other planets

“… Cantor et al [2001] showed that dust storms are frequently spawned at the edges of the two polar cap, at the base of elevated regions in the northern Martian hemisphere, near the polar hood during northern fall and at midlatitudes in both hemispheres. Charging in dust storms that occur in the lower atmosphere was simulated in laboratory experiments and modeled extensively, and it is expected that significant charge is generated within them by triboelectric charging [ Sternovsky et al , 2002; Krauss et al , 2003] and by attachment of galactic cosmic ray‐induced ionization products [ Michael et al , 2008]. The numerical simulation by Melnik and Parrot [1998] suggested that this charging process is very efficient and generates local fields within the dust devil of ∼20 kV m −1 which are sufficient to lead to breakdown (it should be pointed out that the coefficients used by Melnik and Parrot [1998] for CO 2 breakdown were based on Paschen parameters, which may not be applicable in large gap discharges such as expected inside dust storms with several km size).…”