Background
The Planetary Cloud Aerosols Research Facility (PCARF) currently under construction at the Jet Propulsion Laboratory (JPL) is designed to enable experimental investigation into atmospheric aerosol processes on a variety of planets. Cloud formation is studied by injecting particles and pumping saturated vapors into the 3 m tall cylindrical chamber, then inducing convection cells by heating the base and cooling the top of the chamber. PCARF is an improvement on an existing cloud chamber used for terrestrial cloud and aerosol studies and will cover a temperature-pressure space which includes portions of the atmospheres of Venus, Mars, Jupiter, Saturn, Titan, Uranus, and Neptune where atmospheric particles have been observed. Simulations provide a validation on the use of the chamber for these other planetary environments. PlanetCARMA simulates the detailed cloud microphysics and interactions between aerosol particles and gases in a column of atmosphere. PlanetCARMA is set up to simulate a variety of planetary atmospheres.
Approach
The PlanetCARMA code was modified to simulate the environment of a meter-scale cloud chamber rather than a kilometer-scale column of atmosphere. Because PlanetCARMA is a 1-D model, the 3-D environment of the chamber was simulated using multiple independent columns. Initial temperature, pressure, and vertical velocities (simulating the up/downdrafts of the convection cells) were supplied by the System for Atmospheric Modeling (SAM), a large-eddy simulation model used to simulate another cloud chamber. To account for column to column (horizontal) transfer of water vapor and particles, the SAM u, v (velocity) fields were converted to fluxes (multiplying with the calculated gas and particle concentrations in the PlanetCARMA grid cells). These fluxes were included as a source term in the PlanetCARMA vertical transport equation.
Accomplishments
PlanetCARMA was able to simulate cloud formation, growth, and evaporation, using a narrow log-normal distribution of involatile particles to represent the cloud condensation nuclei (CCN) particles that will be injected into PCARF and the water vapor output fields from SAM. The simulations remained stable for the full 30 minutes of model time. Because PlanetCARMA is a bin-microphysics model, the changes in the particle sizes can be tracked in each grid cell over the full simulation. This will help guide experiments in PCARF once the chamber is built and running.