In code units, $R_h=10$ (see previous section), and so one unit of distance in the code corresponds to $l_{unit}=35$ $R_{kpc}$ pc in physical units. The cloud radius is initially set to be 0.2 in code units, or 7 $R_{kpc}$ pc in physical dimensions. The unit of time for Model 3 is given by the ratio $l_{unit}/C_h=0.26~R_{kpc}$ Myr.

In Models 1, 3, and 4, we assume that the WFC is initially at rest. The evolution of the WFC’s is, however, dynamic, with clouds continually colliding and merging, being disrupted by dynamical instabilities, being reheated by conduction from the RHG, cooling to form stars, and condensing out of the RHG. When the clouds form from the RHG, they would be expected to have typical speeds up to the sound speed of the RHG. In Model 2, therefore, we take the WFC to be initially falling in the $-y$ direction, at a velocity equal to $C_h$.

Due to their negative buoyancy, the WFC’s fall through the RHG in all models. If the background RHG is not perturbed, it induces a drag force $F_D$ on WFC’s. For WFC’s with sizes $S$ which are larger than the mean free path of particles in the RHG, 