Venus cloud morphology and motions from ground-based images at the time of the Akatsuki orbit insertion

TL;DR

This study uses ground-based ultraviolet and infrared imaging to analyze Venus's cloud morphology and atmospheric dynamics before the Akatsuki mission, revealing irregular cloud textures and planetary-scale waves.

Contribution

First detailed ground-based observations of Venus's cloud morphology and dynamics around the Akatsuki orbit insertion, using lucky imaging for high-resolution atmospheric analysis.

Findings

Irregular and chaotic upper cloud textures observed in April-June.

Presence of planetary-scale waves and banding in October-December.

Zonal wind velocities consistent with previous measurements.

Abstract

We report Venus image observations around the two maximum elongations of the planet at June and October 2015. From these images we describe the global atmospheric dynamics and cloud morphology in the planet before the arrival of JAXA Akatsuki mission on December the 7th. The majority of the images were acquired at ultraviolet wavelengths (380-410 nm) using small telescopes. The Venus dayside was also observed with narrow band filters at other wavelengths (890 nm, 725-950 nm, 1.435 {\mu}m CO2 band) using the instrument PlanetCam-UPV/EHU at the 2.2m telescope in Calar Alto Observatory. In all cases, the lucky imaging methodology was used to improve the spatial resolution of the images over the atmospheric seeing. During the April-June period, the morphology of the upper cloud showed an irregular and chaotic texture with a well developed equatorial dark belt (afternoon hemisphere), whereas during October-December the dynamical regime was dominated by planetary-scale waves (Yhorizontal, C-reversed and {\psi}-horizontal features) formed by long streaks, and banding suggesting more stable conditions. Measurements of the zonal wind velocity with cloud tracking in the latitude range from 50$^{\circ}$N to 50$^{\circ}$S shows agreement with retrievals from previous works.