  We have obtained a contiguous set of long-slit spectra of a shock wave in the
Cygnus Loop to investigate its structure, which is far from the morphology
predicted by 1D models. Proper motions from Hubble Space Telescope images
combined with the known distance to the Cygnus Loop provide an accurate shock
speed. Earlier analyses of shock spectra estimated the shock speed, postshock
density, temperature, and elemental abundances. In this paper we determine
several more shock parameters: a more accurate shock speed, ram pressure,
density, compression ratio, dust destruction efficiency, magnetic field
strength, and vorticity in the cooling region. From the derived shock
properties we estimate the emissivities of synchrotron emission in the radio
and pion decay emission in the gamma rays. Both are consistent with the
observations if we assume simple adiabatic compression of ambient cosmic rays
as in the van der Laan mechanism. We also find that, although the morphology is
far from that predicted by 1D models and the line ratios vary dramatically from
point to point, the average spectrum is matched reasonably well by 1D shock
models with the shock speed derived from the measured proper motion. A
subsequent paper will analyze the development of turbulence in the cooling zone
behind the shock.
