We do not currently know of any antonyms for cirrocumulus.
The noun cirrocumulus is defined as:
A principal high-level cloud type appearing as a thin, white patch of cloud without shadows, composed of very small droplets in the form of grains or ripples. The elements may be merged or separate, and more or less regularly arranged; they subtend an angle of less than 1° when observed at an angle of more than 30° above the horizon. Holes or rifts often occur in a sheet of cirrocumulus. Abbreviated Cc.
