Microphysical modeling of cirrus 2. Sensitivity studies
- Scripps Institution of Oceanography, La Jolla, CA (United States)
- NASA Ames Research Center, Moffett Field, CA (United States); and others
The one-dimensional cirrus model described in part 1 of this issue has been used to study the sensitivity of simulated cirrus microphysical and radiative properties to poorly known model parameters, poorly understood physical processes, and environmental conditions. Model parameters and physical processes investigated include nucleation rate, mode of nucleation (e.g., homogeneous freezing of aerosols and liquid droplets or heterogeneous deposition), ice crystal shape, and coagulation. These studies suggest that the leading sources of uncertainty in the model are the phase change (liquid-solid) energy barrier and the ice-water surface energy which dominate the homogeneous freezing nucleation rate and the coagulation sticking efficiency at low temperatures which controls the production of large ice crystals (radii greater than 100 {mu}m). Environmental conditions considered in sensitivity tests were CN size distribution, vertical wind speed, and cloud height. The authors found that variations in the total number of condensation nuclei (CN) have little effect on cirrus properties, since nucleation occurs only on the largest CN at the tail of the size distribution. The total number of ice crystals which nucleate depends primarily on the temperature and the cooling rate. Increasing the height of the clouds in the model leads to an increase in ice number density, a decrease in effective radius, and a decrease in ice water content. The most prominent effect of increasing cloud height was a rapid increase in the net cloud radiative forcing which can be attributed to the change in cloud temperature as well as change in cloud ice crystal size distributions. It has long been recognized that changes in cloud height or cloud area have the greatest potential for causing feedbacks on climate change. These results suggest that variations in vertical velocity or cloud microphysical changes associated with cloud height changes may also be important. 27 refs., 10 figs., 1 tab.
- OSTI ID:
- 166200
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: D5 Vol. 99; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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