Aerosol Properties during the 2007 Global Dust Storm (MY28): Solar Infrared Occultation Observations by SPICAM

Abstract : The current analysis deals with properties of aer- osol particles during the 2007 global dust storm (Mars Year 28). Such events are very important for understanding and modeling processes of the Martian climate. During this time a significant dust lifting and transport processes are observed covering the whole planet by dust haze. Atmospheric heating associated with dust absorption of solar light increases strongly making a feedback and causing high advective velocities. These effects are forcing of atmospheric circulation. Solar occultation measurement in the IR spectral range allows to study the vertical distribution of aerosols. SPICAM on Mars-Express is a dedicated occultation experiment. It consists of ultraviolet and infrared spectrometers. Here we analyze data from the SPICAM IR (wavelengths of 1–1.7 μm) which provides information about optical properties of aerosols: opacity and extinction coefficient versus altitude. The ratio of opacities depends primarily on the particle size distribution. Based on Mie scattering theory we can reconstruct such characteristics as effective radius and variance assuming the lognor- mal distribution (Montmessin et al., 2002). Both mineral dust and water ice particles interact with the solar radiation so we have used refraction index for dust (Wolff et al., 2009) and H₂O ice (Warren and Brandt, 2008).