mixing length due to atmospheric stability. The cumulative effect of the progressive reduction in mixing length due to the stability of the Voyager temperature profile above the cloud base is seen to result in a cold-trap in the lower stratosphere. Tripling $f_{\rm rain}$ further reduces the cloud density and lowers the cold-trap to the tropopause; increasing it to 10 results in a cloud with less condensate than the Lewis (1969) model.

We assume that $f_{\rm rain}$ is independent of altitude. Yet specifying an appropriate value of $f_{\rm rain}$ at the cloud base, let alone any vertical dependence, poses a significant challenge. For guidance, first we turn to *in situ* measurements and detailed simulations of terrestrial water clouds, and then consider constraints provided by values retrieved through remote sensing of Jovian ammonia clouds.

For terrestrial stratocumulus clouds capping well-mixed planetary boundary layers, we find that $f_{\rm rain} < 1$ in the cloud deck and increases with distance below cloud top. An assortment of *in situ* measurements indicates that $f_{\rm rain}$ increases with decreasing droplet concentrations ($N$), as fewer and hence larger droplets more efficiently produce drizzle and thereby decrease cloud water. For example, $f_{\rm rain} \sim$ 0.2 for a case study 