  Recent studies have found that cosmic ray transport plays an important role
in feedback processes such as star formation and the launching of galactic
winds. Although cosmic ray buoyancy is widely held to be a destabilizing force
in galactic disks, the effect of cosmic ray transport on the stability of
stratified systems has yet to be analyzed. We perform a stability analysis of a
stratified layer for three different cosmic ray transport models: decoupled
(Classic Parker), coupled with $\gamma_c=4/3$ but not streaming (Modified
Parker), and finally coupled with streaming at the Alfv\'{e}n speed. When the
compressibility of the cosmic rays is decreased the system becomes much more
stable, but the addition of cosmic ray streaming to the Parker Instability
severely destabilizes it. Through comparison of these three cases and analysis
of the work contributions for the perturbed quantities of each system, we
demonstrate that cosmic ray heating of the gas is responsible for the
destabilization of the system. We find that a 3D system is unstable over a
larger range of wavelengths than the 2D system. Therefore, the Parker
Instability with cosmic ray streaming may play an important role in cosmic ray
feedback.
