P1.71 Impacts of ice nucleation modes and ice crystal habits on mixed-phase cloud lifetime

Monday, 28 June 2010
Exhibit Hall (DoubleTree by Hilton Portland)
Barbara Ervens, NOAA, Boulder, CO; and G. Feingold, K. Sulia, and J. Y. Harrington

We explore the influences of, and the feedbacks between, different nucleation modes and ice crystal habit evolution on the lifetimes of mixed-phase clouds. In addition to understanding the growth habits of ice crystals, a parcel model is used to describe detailed ice formation by deposition and immersion nucleation.

Sensitivity studies are performed that cover a wide range of parameters that impact ice nucleation rates and resulting ice mass. These parameters include cloud base temperature, updraft velocity, size distribution and composition of the ice nuclei that nucleate through immersion or deposition freezing. A proxy metric for the cloud lifetime is defined based on the average terminal velocities of the ice particles as a function of their size and habit. Model results are sorted in terms of their impact on cloud lifetime in order to identify the parameter space that most strongly influences cloud lifetime.

It is shown that when the onset of deposition freezing occurs at higher temperatures (> -10°C), habit-influenced growth can have a significant impact on the overall development of the mixed-phase cloud. Feedbacks of habit evolution on supersaturation and subsequent ice nucleation and growth will be discussed.

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