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 ( \sim 70 km height ) , have been studied for decades thanks to their visual contrast in dayside ultraviolet images .
The middle clouds ( \sim 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 .