Keywords:Venus, cloud, near infrared
Venus is our nearest neighbor, and has a size very similar to the Earth's. However, previous observations discovered an extremely dense (92 bar at the surface) and CO2-rich atmosphere, with H2SO4 thick clouds. The Venus cloud consists of H2SO4 main cloud deck at 47 – 70 km, with thinner hazes above and below. The upper haze on Venus lies above the main cloud surrounding the planet, ranging from the top of the cloud (70 km) up to as high as 90 km. Near infrared (0.986 um) dayside image of Venus has taken by solid state imaging (SSI) of the Galileo spacecraft (NASA). It appears almost flat, there are some small scale features with a contrast of 3 %[Belton et al., 1991]. In Takagi and Iwagami. (2011), it may be calculated that the source of the contrast of the order of 3 % in near infrared Venus dayside image is due to variation in the cloud optical thickness. On December 7, 2015, AKATSUKI (JAXA) approached Venus and the Venus orbit insertion was successful. After the Venus orbit insertion, many 0.90 um Venus dayside images were taken by the 1 um near infrared camera (IR1) onboard AKATSUKI. In this study, Venus cloud variations are investigated from 0.90 um Venus dayside images taken by IR1 camera globally. Further, meteorological some changes that contribute to cloud variation are examined in using radiative transfer calculation with high altitude cloud model obtained from Venus Express/SOIR observation. Furthermore, I will introduce observation plan with PIRKA telescope of Hokkaido University.