**AAS 195th Meeting, January 2000**

*Session 51. ISM: Theory and Modelling*

Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall
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## [51.04] Why Would We See 2-D Turbulence in Interstellar Gases?

*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

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