Date of Award
Doctor of Philosophy (PhD)
Atmospheric & Oceanic Sciences
Owen Brian Toon
Douglas E. Kinnison
Charles G. Bardeen
Margaret A. Tolbert
Polar stratospheric clouds (PSCs) are critical elements for polar ozone depletion. A new PSC model coupling stratospheric chemistry, microphysics and climate is constructed and the formation of STS (Super-cooled Ternary Solution) and NAT (Nitric-Acid Trihydrate) PSCs are explored
STS particle properties are dominated by thermodynamics. Simulations of particle volumes and size distributions are generally within the observational error bars. STS particles are not in equilibrium with their environment when the particle surface area is smaller than 4 μm2/cm3. A new nucleation rate equation for NAT is derived based on observed denitrification in the 2010-2011 Arctic winter. The homogeneous nucleation scheme leads to supermicron NAT particles as observed. The simulated the lidar backscatter, and denitrification are generally within observational error bars. However, the simulations are very sensitive to temperature.
Using the same STS and NAT schemes, as well as a prognostic treatment for ice PSC formation and dehydration, the PSCs are simulated during the Antarctic winter of 2010. The current model correctly simulates large NAT particles and denitrification, but cannot produce NAT with high backscattering ratio/number density sometimes observed by CALIPSO. However, our simulated ice has similar backscatter and depolarization which is often attributed to NAT by CALIPSO. Possibly the CALIPSO algorithm misclassifies ice as NAT when the stratosphere is denitrified or dehydrated. STS and NAT form near the pole in May and June, but form a ring outside 80˚S later in the winter when polar HNO3 is depleted. Ice always forms in the coldest area, but becomes less abundant later in the winter.
The model is missing some processes forming NAT such as gravity waves or evaporating ice. These processes should be added to the model in the future.
Zhu, Yunqian, "Microphysical Simulation of Polar Stratospheric Clouds Within the Community Earth System Model" (2015). Atmospheric & Oceanic Sciences Graduate Theses & Dissertations. 57.