[1] The neutral nitrogen and methane measurements made by Ion and Neutral Mass Spectrometer during Cassini flybys T A , T B , and T 5 in Titan's upper atmosphere and exosphere are presented. Large horizontal variations are observed in the total density, recorded to be twice as large during T A as during T 5 . Comparison between the atmospheric and exospheric data show evidence for the presence of a significant population of suprathermal molecules. Using a diffusion model to simultaneously fit the N 2 and CH 4 density profiles below 1500 km, the atmospheric structure parameters are determined, taking into account recent changes in the calibration parameters. The best fits are obtained for isothermal profiles with values 152.8 ± 4.6 K for T A , 149.0 ± 9.2 K for T B , and 157.4 ± 4.9 K for T 5 , suggesting a temperature '5 K warmer at night than at dusk, a trend opposite to that determined by solar-driven models. Using standard exospheric theory and a Maxwellian exobase distribution, a temperature of 20 to 70 K higher would be necessary to fit the T A , T B , and egress-T 5 data above 1500 km. The suprathermal component of the corona was fit with various exobase energy distributions, using a method based on the Liouville theorem. This gave a density of suprathermals at the exobase of 4.4 ± 5.1 Â 10 5 cm À3 and 1.1 ± 0.9 Â 10 5 cm À3 , and an energy deposition rate at the exobase of 1.1 ± 0.9 Â 10 2 eV cm À3 s À1 and 3.9 ± 3.5 Â 10 1 eV cm À3 s À1 for the hot N 2 and CH 4 populations, respectively. The energy deposition rate allowed us to roughly estimate escape rates for nitrogen of '7.7 ± 7.1 Â 10 7 N cm À2 s À1 and for methane of '2.8 ± 2.1 Â 10 7 CH 4 cm À2 s À1 . Interestingly, no suprathermal component was observed in the ingress-T 5 data.

[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.

[1] The charging of aerosols and the conductivity of the lower, night time atmosphere of Mars are calculated. The charge distribution of aerosols was obtained by the simultaneous solution of the ion-aerosol charge balance equations. Galactic cosmic rays are the dominant ionizing process in the night time lower atmosphere producing molecular ions and ion clusters. The ion production rates for different solar activities are considered. The ion-ion recombination rates and the ion-aerosols attachment coefficients are calculated for altitudes from 0 to 70 km. Both the steady state and time dependent concentration of charged aerosols are calculated. The conductivity produced by ion-attachment of aerosols was found to decrease by a factor of five yielding a value of about 4 Â 10 À12 Ohm À1 m À1 close to the surface. The effect on the conductivity of the temperature vs. altitude and the aerosol density are also estimated.

Abstract. Electrified aerosols have been observed in the lower troposphere and in the mesosphere, but have never been detected in the stratosphere and upper troposphere. We present measurements of aerosols obtained during a balloon flight to an altitude of ∼ 24 km. The measurements were performed with an improved version of the Stratospheric and Tropospheric Aerosol Counter (STAC) aerosol counter dedicated to the search for charged aerosols. It is found that most of the aerosols are charged in the upper troposphere for altitudes below 10 km and in the stratosphere for altitudes above 20 km. Conversely, the aerosols seem to be uncharged between 10 km and 20 km. Model calculations are used to quantify the electrification of the aerosols with a stratospheric aerosol-ion model. The percentages of charged aerosols obtained with model calculations are in excellent agreement with the observations below 10 km and above 20 km. However, the model cannot reproduce the absence of electrification found in the lower stratosphere, as the processes leading to neutralisation in this altitude range are unknown. The presence of sporadic transient layers of electrified aerosol in the upper troposphere and in the stratosphere could have significant implications for sprite formation.

The "online" meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF-Chem) model has been implemented over the Indian subcontinent for three consecutive summers in 2008, 2009 and 2010 to study the aerosol properties over the domain. The initial and boundary conditions are obtained from NCAR reanalysis data. The emission rates of sulfur dioxide, black carbon, organic carbon and PM_2.5, which are developed over India at a grid resolution of 0.25° × 0.25° have been used in the present study. The remaining emissions are obtained from global inventories (RETRO and EDGAR). The model simulated the meteorological parameters, trace gases and particulate matter. Predicted mixing ratios of trace gases (Ozone, carbon monoxide and sulfur dioxide) are compared with ground based observations over Kanpur. Simulated aerosol optical depth are compared with those observed at nine Aerosol Robotic Network stations (AERONET). The simulations show that the aerosol optical depth of the less polluted regions is better simulated compared to that of the locations where the aerosol loading is very high. The vertical profiles of extinction coefficient observed at Kanpur Micropulse Lidar Network (MPLNET) station is in agreement with the simulated values for altitudes greater than 1.5 km and qualitatively simulate the elevated layers of aerosols. The simulated mass concentration of black carbon shows very good correlation with observations, due to the better local emission inventory used. The vertical profiles of black carbon at various locations have also been compared with observations from aircraft campaign held during pre-monsoon period of 2008 and 2009 resulting in good agreement. This study shows that WRF-Chem model captures many important features of the observations and therefore can be used for understanding and predicting regional atmospheric composition over Indian subcontinent