# Morphology and dynamics of Venus's middle clouds with Akatsuki/IR1

## TL;DR

This study analyzes Venus's middle cloud morphology and wind dynamics using near-infrared images from Akatsuki, revealing hemispherical asymmetries, sharp discontinuities, and long-term wind variations at lower latitudes.

## Contribution

First extensive analysis of Venus's middle cloud morphology and motions at lower latitudes using IR1 images, uncovering asymmetries, discontinuities, and long-term wind variations.

## Key findings

- Hemispherical asymmetries every 4-5 days.
- Sharp discontinuities in cloud structures.
- Long-term wind variations of 20 m/s over 10 years.

## Abstract

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.