Are HVCs produced in Galactic fountains?

Three-dimensional simulations of the disk-halo interaction show the formati on of a thick HI and HII gas disk with different scale heights. The thick H I disk prevents the disk gas from expanding freely upwards, unless some hig hly energetic event such as chimneys occurs, whereas the thick HII disk act s as a disk-halo interaction region from where the hot ionized gas flows fr eely into the halo. The upflowing gas reaches the maximum height at z simil ar to 9.3 +/- 1 kpc becoming thermally unstable due to radiative losses, an d condenses into HI clouds. Because the major fraction of the gas is gravit ationally bound to the Galaxy, the cold gas returns to the disk. The descen ding clouds will have at some height high velocities. In a period of 200 My r of fountain evolution, some 10 percent of the total number of clouds are HVCs.