| Summary: | This dissertation contains three studies investigating processes within mixed phase clouds. The first study examines the ice habit (shape) assumptions used in microphysics schemes. Ice habit is greatly simplified in models, and uncertainties remain in how to best model ice processes. We simulate a Sierra Nevada snowstorm driven by an atmospheric river. We have simulated the storm with four fixed-habit types as well as with an ice habit scheme that is variable in time and space. In contrast to some previous studies, we found substantially smaller sensitivity of total accumulated precipitation amount and negligible changes in spatial distribution to the ice habit specification. The reason for smaller sensitivity seems to be linked to strong aggregation of ice crystals in the model. Nonetheless, while changes in total accumulated precipitation were small, changes in accumulated ice hydrometeors were larger. The variable-habit simulation produced up to 37% more ice precipitation than any of the fixed-habit simulations with an average increase of 14%. The variable-habit simulation led to a maximization of ice growth in the atmosphere and, subsequently, ice accumulation at the surface. This result points to the potential importance of accounting for the time and space variation of ice crystal properties in simulations of orographic precipitation.The next two studies concern mixed-phase stratocumulus clouds in the Arctic. These clouds are ubiquitous in the Arctic, and can persist for days and dissipate in a matter of hours. The first of these two studies concerns aerosol-limited dissipation. It is sometimes unknown what causes the observed sudden dissipation of these clouds, but aerosol-cloud interactions may be involved. Arctic aerosol concentrations can be low enough to affect cloud formation and structure, and it has been hypothesized that, in some instances, concentrations can drop below some critical value needed to maintain a cloud. We use observations from a Department of Energy ARM site on the northern slope of ...
|
|---|