Impact of cloud-base turbulence on CCN activation: Single-size CCN

CCN are assumed in 200-cm(-3) concentration in all cases. Mean cloud-base updraft velocities of 0.33, 1, and 3 m s(-1) are considered. In the nonturbulent parcel, all CCN are activated and lead to a monodisperse droplet size distribution above the cloud base, with practically the same droplet size in all simulations.

In contrast, turbulence can lead to activation of only a fraction of all CCN with a nonzero spectral width above the cloud base, of the order of 1 mu m, especially in the case of small CCN and weak mean cloud-base ascent. We compare our results to studies of the turbulent single-size CCN activation in the Pi chamber. Sensitivity simulations that apply a smaller turbulence intensity, smaller computational domain, and modified initial conditions document the impact of specific modeling assumptions.

The simulations call for a more realistic high-resolution modeling of turbulent cloud-base activation.