Latitude Dependence of the Venus Cloud System Radiative-Dynamic Feedback

The clouds and aerosols of Venus constitute a nearly 40 km thick region (when considering both the clouds and historically-named hazes) that is sustained by a strongly coupled combination of multiple physical processes including cloud microphysics, photochemistry, solar heating and radiative cooling, and mesoscale and global dynamics.  Though simplifications can be made by ignoring or holding constant some of these processes, faithful simulation of these clouds and aerosols requires consideration of this coupling.  We present here a first 1D model of the Venus clouds and aerosols between 40 km and 80 km altitude that simultaneously calculates cloud microphysics, simplified diurnally-varying photochemical production and loss, radiative transfer, diurnally-varying solar heating, radiative cooling, and parameterized convective mixing.

This model is built on the PlanetCARMA framework, which has previously been shown to accurately reproduce the Venus clouds and aerosols when simulating microphysics, simplified diurnally-varying photochemistry, and vertical mixing dictated by a parameterized eddy diffusion coefficient that was static in time.  Here, we re-apply the radiative dynamic feedback that had been previously applied by the authors to a 40 km to 60 km microphysics model of the Venus Clouds.  This involves coupling to that microphysics model the delta-scaled two-stream radiative transfer model that is already part of PlanetCARMA, as well as the addition of a time-varying eddy diffusion coefficient that is calculated as a function of the vertical gradient of the potential temperature by means of a Richardson Number parameterisation.

We show that this updated radiative-dynamic feedback model of nearly the entire domain occupied by condensed sulfuric acid in the atmosphere of Venus faithfully reproduces the observed distribution of the clouds in terms of Cloud Liquid Content, effective radius, Photochemical, Condensational, and Total Cloud opacity, and cloud column abundance; it also produces emitted nightside near infrared radiances consistent with observations.  Long-period (on the order of an Earth-year) oscillations are seen in some simulations.  We also compare with observations the variations in the vertical structure of the simulated Venus clouds and hazes as a function of latitude, quantifying their dependence upon changes in the photochemistry and cloud top radiative cooling that results from the changing Sun angle with both time and latitude.

Observations of the clouds of Venus exhibit variations at a wide range of spatial and temporal scales.  Completion of this model brings us another step closer to being able to determine the root causes of these variations and better understand the role of clouds in the climate and evolution of Venus and other rocky planets.