\added 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 on the variability of the cloud albedo at 365 nm and its impact on Venus’ solar heating rates based on an analysis of Venus Express and Akatsuki ’ s UV images , and Hubble Space Telescope and MESSENGER ’ s UV spectral data ; in this analysis the calibration correction factor of the UV images of Venus Express ( VMC ) 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 H _ { 2 } SO _ { 4 } -H _ { 2 } O aerosol formation . \deleted The ultraviolet ( UV ) to visible spectrum of Venus has a broad absorption feature which peaks at 360 nm due to the presence of an unknown absorber near the cloud top level ( around 70 km ) .
While the chemical composition of the unknown absorber has been a 4-decade old mystery , it is known that about half of the solar energy is deposited in the atmosphere due to this absorber .
Thus , the unknown absorber plays a critical role in the atmospheric energy balance .
Here we present a quantitative study on the variability of the cloud albedo at 365 nm and its impact on Venus’ solar heating rates based on an analysis of Venus Express and Akatsuki ’ s UV images , and Hubble Space Telescope and MESSENGER ’ s UV spectral data .
These results show that the 365-nm albedo varied by a factor of 2 from 2006 to 2017 over the planet .
Our radiative transfer calculations show that the observed 365-nm albedo variation can produce a 25–40 % change in the low latitude solar heating rate , and therefore that the cloud top level atmosphere should have experienced considerable solar heating variations over this period .
We suggest that this variable solar heating may explain the reported Venus’ zonal wind variations from 2006 to 2017 , and show the plausible process through global circulation model calculations .
Further studies are required to understand possible climate change on the current Venus in response to the inferred solar heating variations .