The Influence of Cloud Condensation Nucleus Coagulation on the Venus Cloud Structure

We present the Venus version of PlanetCARMA and demonstrate the significance of coagulation properties on the structure of the Venus cloud system. The composition of the smallest mode of particles in the Venus atmosphere, which likely serve as cloud condensation nuclei (CCN), is unknown. Here we demonstrate that a change in the ability of CCN to grow via coagulation in the Venus atmosphere can produce measurable short-term and long-term signatures in the Venus cloud structure. Specifically, we find that the existence of a population of CCN that is prevented from growing via coagulation will result in an overall reduced total cloud opacity and can, under some conditions, produce long-term (on the order of several hundred days) variations in both the photochemical cloud opacity (above 57 km) and the condensational cloud opacity (below 57 km). While we show that these variations do not appear to be the source of the short-timescale cloud opacity variations seen on the nightside near-infrared emission of Venus, it is possible that they may contribute to the longer-term variations seen over the 2.5 yr lifetime of the VIRTIS-M-IR instrument on Venus Express. We recommend further modeling studies to investigate wider ramifications of this behavior, as well as further laboratory studies to better constrain the microphysical properties of the aerosols that can make up the Venus clouds.