  Radiative shock waves in the Cygnus Loop and other supernova remnants show
different morphologies in [O III] and H{\alpha} emission. We use HST spectra
and narrowband images to study the development of turbulence in the cooling
region behind a shock on the west limb of the Cygnus Loop. We refine our
earlier estimates of shock parameters that were based upon ground-based
spectra, including ram pressure, vorticity and magnetic field strength. We
apply several techniques, including Fourier power spectra and the Rolling Hough
Transform, to quantify the shape of the rippled shock front as viewed in
different emission lines. We assess the relative importance of thermal
instabilities, the thin shell instability, upstream density variations, and
upstream magnetic field variations in producing the observed structure.
