HR: 15:10h
AN: P33C-07    [Abstracts]
TI: Aerosol Charging by Ion Attachment and Electrical Conductivity in the Lower Atmosphere of Mars
AU: * Tripathi, S N
EM: snt@iitk.ac.in
AF: Indian Institute of Technology, Department of Civil Engineering Indian Institute of Technology, Kanpur, UP 208016, India
AU: Michael, M
EM: mary@iitk.ac.in
AF: Indian Institute of Technology, Department of Civil Engineering Indian Institute of Technology, Kanpur, UP 208016, India
AB: Aerosol in the atmosphere of Mars is a topic of considerable interest since their effect on the climate has been recognized. The aerosols interact with both visible and infrared radiation and modify atmospheric heating rates which are responsible for the atmospheric circulation, dust storms etc. In the present work, the charging of aerosols and the conductivity of the lower atmosphere of Mars during the day and night-time are calculated. Galactic cosmic rays are the dominant ionizing process in the lower atmosphere producing molecular ions and ion clusters. These ion clusters get attached to the aerosols and charging occurs during the night-time. Solar UV photons are an additional ionizing agent during the day-time. Solar photons of energy less than 6 eV reach the surface of Mars as those with energies greater than 6 eV are absorbed by the atmospheric molecules before they reach the lower atmosphere. Those photons, which 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 are calculated. The neutral atmospheric properties required to calculate the aerosol charging and the conductivity are obtained from Magalhaes et al. (1999). The aerosols have a concentration and effective radius of 2.26 cm-3 and 1.9 mm, respectively, at the surface. The charge distribution of aerosols is obtained by the simultaneous solution of the ion-electron-aerosol charge balance equations. Both the steady state and time dependent concentration of charged aerosols are calculated. It was observed that about 80% of the aerosols close to the surface become charged during the night-time (Michael et al., 2007). In addition to ions, electrons are also present during the day-time. More charging occurs and most of the aerosols become charged during the day-time. The conductivity of the lower atmosphere is also estimated and it was found that the presence of aerosols reduces the conductivity. The effect of different temperature structures, solar conditions and aerosol concentration on the conductivity will be presented. The variation in conductivity during the dust storm of 2001 will also be discussed. References Magalhaes, J.A., Schofield, J.T., and A. Seiff, Results of the Mars Pathfinder atmospheric structure investigation, J. Geophys. Res., 104, 8943-8955, 1999. Michael, M., M. Barani, and S. N. Tripathi, Numerical predictions of aerosol charging and electrical conductivity of the lower atmosphere of Mars, Geophys. Res. Lett., 34, L04201, 10.1029/2006GL028434, 2007.
UR: http://home.iitk.ac.in/~snt
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 5400 PLANETARY SCIENCES: SOLID SURFACE PLANETS
DE: 5405 Atmospheres (0343, 1060)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting