Venus cloud opacity from the Venus Express observations in the near-IR transparency “windows”

Imaging of the Venus night side in the near-infrared spectral transparency “windows” at 1, 1.7 and 2.3 µm by Venus Express revealed details of the deep cloud structure and total opacity variations. These observations provide important clues for understanding of the atmospheric and cloud dynamics and the energy balance in the thick Venusian atmosphere. The most remarkable change of the cloud opacity occurs at about 60 S latitude where the emission from the deep atmosphere strongly decreases that corresponds to abrupt transition to the much thicker polar cloud with almost doubled total opacity. We will present results of the radiative transfer modelling by the Spherical Harmonics Discrete Ordinates Method (SHDOM) simulating outgoing emission on the night side and preliminary assessments of the total cloud opacity and its variability.