A numerical model of the cloud-topped planetary boundary-layer: influence of the physico-chemical properties of aerosol particles on the effective radius of stratiform clouds

The present investigation deals with the impact of different aeorosol types on the value of the effective radius of stratiform clouds. In several numerical sensitivity studies with the microphysical stratus model MISTRA, the aerosol composition was linearly changed from pure maritime to pure rural aerosol particles. Numerical results show that in environments with pure maritime aerosols, the effective radius is usually much larger than in continental regions. Values of the effective radius are also time-dependent with minima and maxima during day and night, respectively. In precipitating clouds, the effective radius might achieve values larger than 30 mm. In continental regions, the effective radius is relatively small with values below 10 mm. The numerical results also show that a small contribution of the rural aerosol to the total aerosol number concentration already has a strong impact on the value of the effective radius. According to these findings, it is recommended to use in large-scale models the lower continental values of the effective radius in all regions over the ocean which are affected by continental air masses. q 2000 Elsevier Science B.V. All rights reserved.