The Venusian atmosphere is covered by clouds with super-rotating winds whose accelerating mechanism is still not well understood. The fastest winds, occurring at the cloud tops (∼70 km height), have been studied for decades thanks to their visual contrast in dayside ultraviolet images. The middle clouds (∼50-55 km) can be observed at near-infrared wavelengths (800-950 nm), although with very low contrast. Here we present the first extensive analysis of their morphology and motions at lower latitudes along 2016 with 900-nm images from the IR1 camera onboard Akatsuki. The middle clouds exhibit hemispherical asymmetries every 4-5 days, sharp discontinuities in elongated "hook-like" stripes, and large contrasts (3-21%) probably associated with large changes in the optical thickness. Zonal winds obtained with IR1 images and with ground-based observations reveal mean zonal winds peaking at the equator, while their combination with Venus Express unveils long-term variations of 20 m s−1 along 10 years.
@article{arxiv.1903.02883,
title = {Morphology and dynamics of Venus's middle clouds with Akatsuki/IR1},
author = {J. Peralta and N. Iwagami and Sánchez-Lavega and Y. J. Lee and R. Hueso and M. Narita and T. Imamura and P. Miles and A. Wesley and E. Kardasis and S. Takagi},
journal= {arXiv preprint arXiv:1903.02883},
year = {2019}
}