Mesospheric Clouds on Earth and Mars

This thesis comprises experimental investigations regarding the microphysical processes occurring within mesospheric clouds on Earth and Mars. CO2 trapping in amorphous ice was investigated with relevance to Earth’s mesosphere as a possible temporary sink of gas phase CO2. Experimental limits to the trapping process were evaluated and extrapolated to mesospheric conditions. This process was shown to be only plausible under extreme conditions. Metal deposition on low temperature ice was also investigated with relevance to PMCs. The reactivity of Mg and K was evaluated experimentally and with electronic structure calculations. A secondary Meteoric smoke Particle (MSP) formation process was hypothesised, with calculations suggesting this will impact the distribution of MSPs in the mesosphere during cloud season. In regards to the Martian mesosphere, microphysical processes that influence CO2 cloud formation have been investigated using a novel experimental system. Mass distributions of CO2 nucleation on nanoparticles were used to determine variables critical to modelling CO2 cloud formation. It is predicted here that lower temperatures than previously thought would be required to form CO2 clouds in the mesosphere. The crystal structure of CO2 ice under Martian conditions has also been experimentally investigated, with a cubic crystal structure determined (CO2-I). Temperature dependent parameters of CO2-I were applied to rates of nucleation and sedimentation for CO2 ice particles.