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A. Minter (NRAO)
Neutral gas in the galaxy traced through the HI 21 cm line and the CO (J 1arrow0) line, as well as the ionized gas seen in H\alpha and radio recombination lines have power spectra of density, column density and velocity whose slopes are consistent with 2-Dimensional turbulence on large spatial scales (\gtrsim 0.01-1~pc). We know, however, from in situ measurements that the turbulence in fluids on the Earth and in the solar wind is fully 3-Dimensional. We have every reason to expect the observed turbulence in the interstellar medium to be 3-Dimensional also.
A method had been devised to make ``snapshot'' models of the density and velocity fields of a turbulent gas. The desired power spectra (density and velocity) are the only inputs into the model. These models have been used to study how propagation effects and the various modes of observing can change the 3-Dimensional Kolmogorov-like turbulence input into the models into the observed 2-Dimensional turbulence. The following effects can make the observed turbulence appear 2-Dimensional: 1) if the turbulence is contained in a thin filament or slab; 2) if the medium has a high optical depth; and 3) if any method of observation or analysis is used which effectively limits the emission from the medium under study to a thin slab, for example, by analyzing an individual channel map. Straightfoward analysis of data leads to misleading or incomplete results if these effects are not taken into account.
The author(s) of this abstract have provided an email address for comments about the abstract: tminter@nrao.edu