| This study concerns the investigation of the form of the wavenumber spectrum of the Galactic electron density fluctuations through an examination of the scattering of the radio pulses emitted by pulsars as they propagate through the diffuse ionized interstellar gas. A widely used model for the electron density spectrum is based on the simple power-law: {dollar}Psb{lcub}nsb{lcub}e{rcub}{rcub}(q)propto qsp{lcub}-beta{rcub}{dollar}, where {dollar}beta = 11/3{dollar} is usually assumed, corresponding to Kolmogorov's turbulence spectrum. The simple Kolmogorov model provides satisfactory agreement for observations along many lines of sight; however, major inconsistencies remain. The inconsistencies suggest that an increase in the ratio of the power between the high ({dollar}10sp{lcub}-8{rcub}{lcub}rm m{rcub}sp{lcub}-1{rcub}leq qleq10sp{lcub}-7{rcub}{lcub}rm m{rcub}sp{lcub}-1{rcub}{dollar}) and low ({dollar}10sp{lcub}-13{rcub}{lcub}rm m{rcub}sp{lcub}-1{rcub}leq qleq10sp{lcub}-12{rcub}{lcub}rm m{rcub}sp{lcub}-1{rcub}{dollar}) wavenumbers is needed. This enhancement in the ratio can in turn be achieved by either including an inner scale, corresponding to a dissipation scale for the turbulent cascade, in the Kolmogorov spectrum or by considering steeper spectra. Spectra with spectral exponents {dollar}beta > 4{dollar} have been in general rejected based on observations of pulsar refractive scintillations. The special case of {dollar}beta = 4{dollar} has been given little attention and is analyzed in detail. Physically, this "{dollar}beta{dollar} = 4" model corresponds to the random distribution, both in location and orientation, of discrete objects with relatively sharp boundaries across the line of sight. An outer scale is included in the model to account for the average size of such objects. We compare the predictions of the inner-scale and {dollar}beta{dollar} = 4 models both with published observations and observations we made as part of this investigation. We conclude that the form of the wavenumber spectrum is dependent on the line of sight. We propose a composite spectrum featuring a uniform background turbulence in presence of randomly distributed discrete objects, as modeled by the {dollar}beta{dollar} = model. |
