  We investigate the structure and evolution of a geometrically thin viscous
Keplerian circumbinary (CB) disk, using detailed models of their
radiative/convective vertical structure. We use a simplified description for
the evolution of the cataclysmic binary and focus on cases where the
circumbinary disk causes accelerated mass transfer (> 1e-8 Msun/yr). The inner
edge of the disk is assumed to be determined by the tidal truncation radius and
the mass input rate into the disk is assumed to be a small fraction (1e-5-0.01)
of the mass transfer rate. Under the action of the viscous stresses in the disk
the matter drifts outward with the optically thick region extending to several
AU. The inner part of the disk is cool with maximum effective temperatures <
3,000 K while the outermost parts of the disk are < 30 K and optically thin. We
calculate the effects of thermal instability on a sufficiently massive CB disk.
It leads to outbursts reminiscent of those in thermally unstable accretion
disks, with the instability remaining confined to the inner regions of the CB
disk. However, for most of the evolutionary sequences the surface densities
required to trigger instability are not reached. The spectral energy
distributions from circumbinary disks are calculated, and the prospects for the
detection of such disks in the infrared and submm wavelength regions are
discussed.
