Representing the Fate of Springtime Arctic Clouds.

Abstract

Observations and modeling results have shown the high latitudes’ environment changing in a warmer climate. The research presented focuses on the parameterizations used to simulate Arctic Mixed-Phase Stratocumulus (AMPS) clouds and the sensitivity of the AMPS to changing environmental conditions. A Large Eddy Simulation (LES) is used to reproduce an idealized AMPS during the intensive observation period, Indirect and Semi-Direct Aerosol Campaign (ISDAC). The level of complexity needed to simulate this cloud is investigated with two microphysics routines and two subgrid scale turbulent closure models. It was found that both the microphysics routines accurately produced macrophysical properties of the observed cloud, and that the less computationally expensive microphysics parameterization could be used to reproduce the AMPS. When the subgrid scale turbulent closure models were evaluated with the microphysics routines, it was found the choice of turbulent closure model had more of an effect on the cloud properties than the choice of microphysics.

Knowledge of the parameterizations needed for representing the AMPS were applied to a parameter-space-filling uncertainty quantification technique to understand the sensitivity of the mixed-phase cloud to changes in its environment. The LES model was connected to the uncertainty quantification toolkit, Design Analysis Kit for Optimization and Terascale Applications (DAKOTA), which produced parameter ranges from which the LES model tried to produce a boundary layer mixed-phase cloud. The environmental variables that were changed were the cloud ice and aerosol concentration, surface sensible and latent heat fluxes, and large scale temperature, water vapor, and vertical motion. Four characteristic behaviors were used to classify the fates of the AMPS: stability, growth, decay, and dissipation. It was found the longevity and spatial extent of the AMPS were most sensitive to changes in large-scale temperature, water vapor, and vertical motion in the variable ranges that were investigated. It was also found the AMPS did not form unconditionally, and that environmental thresholds existed which made mixed-phase cloud formation conducive.