Galactic distribution of interstellar scattering matter

It is shown that existing data on the scattering of radio waves from discrete sources by the interstellar medium can be reconciled if it is accepted that the amplitude of the electron-density irregularities rises towards the galactic center. This behavior offers a natural explanation for the observed dependence of the decorrelation bandwidth and the width of the scintillation spectrum on the dispersion measure of pulsars. The distribution of scattering matter in space, the characteristic amplitude of the electron-density fluctuations, and the large velocity dispersion of the scattering irregularities can all be understood by assuming that the scattering regions are associated with places where energy is released in the Galaxy, namely H II regions and supernova envelopes. Furthermore, regions of well-developed turbulence should be embedded in a medium that is relatively weakly turbulized.