Optical properties of the Venus upper clouds from the data obtained by Venus Monitoring Camera on-board the Venus Express ☆

Abstract During more than 6 years of the Venus Express (VEx) mission, the Venus Monitoring Camera (VMC) took around 300 000 images in four channels covering almost all the latitudes, including night and day sides. Here we give an overview of the VMC data and summarize results of retrievals of the optical properties of the Venus upper clouds. The in-flight characterization and calibration of VMC are also described. We model the phase dependence of brightness (phase range α = 0 – 140 ° ) retrieved from the dayside images obtained in NIR1 VMC channel at various latitudes (30°N–60°S) and local solar times (6–18 h). The radiative transfer calculations were performed for the plane-parallel atmospheric layers, and the Mie theory was used for the calculations of the single scattering phase functions of the cloud aerosols. The size distribution of cloud particles and their refractive index were estimated for each of the regions observed. These retrievals show some temporal and spatial variations. In general, the particles at low latitudes are somewhat larger than in the regions closer to the southern pole ( R eff = 1.2 – 1.4 μ m versus 0.9 – 1.05 μ m ). At latitudes 40°S–60°S the refractive index is usually smaller than in the other regions ( m r = 1.44 – 1.45 versus 1.45–1.47 with sporadic spikes of up to 1.49). The retrievals robustly show presence of particles with a radius of about R eff = 0.9 μ m in the clouds and/or the haze above them in these mid-latitudes. Small submicron ( R eff = 0.23 μ m ) particles are detected mostly in the morning.