Enormous Cloud Cover on Venus observed by Akatsuki’s IR2 data recovered by Restoration-by-Deconvolution (RD) method

Abstract We have developed a new method ‘Restoration by Deconvolution’ (RD) to restore nightside photometry in the Akatsuki/IR2 images contaminated by spread light from intense dayside crescent. With updated point spread function model for IR2 and incorporation of radiative transfer computations, our RD-method is able to improve the photometric accuracy of nightside emission data in both 2.26µm and 1.735µm filters. Exploiting the enhanced photometric quality, the ‘Enormous Cloud Cover’ (ECC) features observed in both 2016-08-18 and 2016-08-27 data have been investigated. Possible altitude variations in the ECC’s spatial variation measurements from z=52km up to z=60km were found. The observations were interpreted that ECC constituting of large sulfuric acid droplets (mean radius of 3.65µm and the optical thickness ~7-9) experience strong upwelling near the ECC front. This elevates the aerosols up to z=58-60km, then subjected upon by strong downwelling forces the particles to sink by a velocity ~-0.3m/s. The analyses of physical properties and evolutionary behavior of the ECC on both dates (08-18 and 08-27) suggest them to be recurring phenomena in the lower part of Venus’ clouds.