Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express , Akatsuki , MESSENGER , and the Hubble Space Telescope

Yeon Joo Lee (1, 2) , Kandis-Lea Jessup (3) , Santiago Perez-Hoyos (4) , Dmitrij V. Titov (5) , Sébastien Lebonnois (6) , Javier Peralta (7) , Takeshi Horinouchi (8) , Takeshi Imamura (1) , Sanjay Limaye (9) , Emmanuel Marcq (10) , Masahiro Takagi (11) , Atsushi Yamazaki (7, 12) , Manabu Yamada (13) , Shigeto Watanabe (14) , Shin-Ya Murakami (7) , Kazunori Ogohara (15) , William Mcclintock (16) , Gregory Holsclaw (16) , Anthony Roman (17)

1 Graduate School of Frontier Sciences [Kashiwa]
2 ZAA - Zentrum für Astronomie und Astrophysik [Berlin]
3 SwRI - Southwest Research Institute [Boulder]
4 Departamento de Fisica Aplicada [Bilbao]
5 ESTEC - European Space Research and Technology Centre
6 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
7 ISAS - Institute of Space and Astronautical Science
8 Faculty of Environmental Earth Science [Sapporo]
9 SSEC - Space Science and Engineering Center [Madison]
10 PLANETO - LATMOS
11 Kyoto Sangyo University
12 Department of Earth and Planetary Science [Tokyo]
13 PERC - Planetary Exploration Research Center [Chiba]
14 Hokkaido Information University
15 University of Shiga Prefecture
16 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
17 STSci - Space Telescope Science Institute

An unknown absorber near the cloud-top level of Venus generates a broad absorption feature from the ultraviolet (UV) to visible, peaking around 360 nm, and therefore plays a critical role in the solar energy absorption. We present a quantitative study of the variability of the cloud albedo at 365 nm and its impact on Venus's solar heating rates based on an analysis of Venus Express and Akatsuki UV images and Hubble Space Telescope and MESSENGER UV spectral data; in this analysis, the calibration correction factor of the UV images of Venus Express (Venus Monitoring Camera) is updated relative to the Hubble and MESSENGER albedo measurements. Our results indicate that the 365 nm albedo varied by a factor of 2 from 2006 to 2017 over the entire planet, producing a 25%-40% change in the low-latitude solar heating rate according to our radiative transfer calculations. Thus, the cloud-top level atmosphere should have experienced considerable solar heating variations over this period. Our global circulation model calculations show that this variable solar heating rate may explain the observed variations of zonal wind from 2006 to 2017. Overlaps in the timescale of the long-term UV albedo and the solar activity variations make it plausible that solar extreme UV intensity and cosmic-ray variations influenced the observed albedo trends. The albedo variations might also be linked with temporal variations of the upper cloud SO 2 gas abundance, which affects the H₂SO₄-H₂O aerosol formation.

Keywords: planets and satellites: atmospheres; planets and satellites: individual (Venus); planets and satellites: terrestrial planets

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

Yeon Joo Lee, Kandis-Lea Jessup, Santiago Perez-Hoyos, Dmitrij V. Titov, Sébastien Lebonnois, et al.. Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express , Akatsuki , MESSENGER , and the Hubble Space Telescope. The Astronomical Journal, 2019, 158 (3), pp.126. ⟨10.3847/1538-3881/ab3120⟩. ⟨insu-02283341⟩