  We discuss an idea whether spherical blast waves can amplify by a non-local
resonant hydrodynamic mechanism inhomogeneities formed by turbulence or phase
segregation in the interstellar medium. We consider the problem of a
blast-wave-turbulence interaction in the Linear Interaction Approximation.
Mathematically, this is an eigenvalue problem for finding the structure and
amplitude of eigenfunctions describing the response of the shock-wave flow to
forced oscillations by external perturbations in the ambient interstellar
medium. Linear analysis shows that the blast wave can amplify density and
vorticity perturbations for a wide range of length scales with amplification
coefficients of up to 20, with amplification the greater, the larger the
length. There also exist resonant harmonics for which the gain becomes formally
infinite in the linear approximation. Their orbital wavenumbers are within the
range of macro- ($l \sim 1$), meso- ($l \sim 20$) and microscopic ($l > 200$)
scales. Since the resonance width is narrow: typically, $\Delta l <1$,
resonance should select and amplify discrete isolated harmonics. We speculate
as to a possible explanation of an observed regular filamentary structure of
regular-shaped round supernova remnants such as SNR 1572, 1006 or 0509-67.5.
Resonant mesoscales found ($l \approx 18 $) are surprisingly close to the
observed scales ($l \approx 15$) of ripples in the shell's surface of SNR
0509-67.5.
