  In a recent paper [Y. Taroyan, Phys. Rev. Lett 101, 245001 (2008) it is
claimed that a new MHD instability of the Alfven wave has been found:
incompressible Alfven modes propagating in a compressible spatially varying
flow were apparently exponentially amplified. We show that the results of the
work follow from an impossible equilibrium and therefore should be disregarded.
