  We present non-adiabatic hydrodynamic simulations of a supersonic light jet
propagating into a fully ionized medium of uniform density on a scale
representative of the narrow line region (NLR) in Seyfert galaxies with
associated radio jets. In this regime the cooling distance of the swept up gas
in the bowshock of the jet is of the same order as the transverse extent of the
jet bowshock, as opposed to the more extreme regimes found for more powerful
adiabatic large scale jets or the slow galactic jets which have been simulated
previously. We calculate the emissivity for the H_alpha line and radio
synchrotron emission. We find that the structure of the line emitting cold
envelope of the jet cocoon is strongly dependent on the non-stationary dynamics
of the jet head as it propagates through the ambient medium. We observe the
formation of cloud-like high density regions which we associate with NLR clouds
and filaments. We find that some of these clouds might be partially neutral and
represent sites of jet induced star formation. The calculated H_alpha flux and
the spectral line width are consistent with NLR observations. The simulation of
the radio-optical emission with radiative cooling confirms the basic result of
the geometric bowshock model developed by Taylor et al. (1989) that the start
of noticeable optical line emission can be significantly offset from the
hotspot of the radio emission. However, the time-dependent nature of the jet
dynamics implies significant differences from their geometric bowshock model.
