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Studies of stratocumulus cloud, drizzle and aerosol interaction




Chen, Aidong, author

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A stratocumulus-capped marine mixed layer model has been developed. It focuses on a new parameterization of drizzle which is regulated by a predicted CCN number con- centration. When the CCN number concentration increases, the drizzle rate decreases, so that the boundary-layer cloud remains thick. When the CCN number concentration decreases, the drizzle rate increases and as a result, the boundary-layer cloud becomes thinner. The boundary layer's macroscopic structure is thus sensitive to the CCN number concentration. Aerosol particles in this model are divided into two modes. One represents the small nucleation mode particles, and the other represents the CCN mode particles. Both number and mass balances are considered in this report. Two steady states are obtained, similar to the results of Baker and Charlson (1990). The lower steady state CCN number concentration corresponds to the typical marine time boundary layer. The higher steady state CCN number concentration is regarded as the continental air mass case. A difference between the results from this model and those reported by Baker and Charlson (1990) is that a smoother transition between these two states is found. This result supports some observations that suggest there is no sharp transition between the drizzling and non-drizzling steady states of CCN number concentration in the marine boundary layer. The model is tested using ASTEX observational data. The model results are in good agreement with the observations.


April 1996.
Also issued as author's thesis (M.S.) -- Colorado State University, 1996.

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Cloud physics
Boundary layer (Meteorology)


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