INTERFEROMETRIC SEEING MEASUREMENTS ON MT WILSON - POWER SPECTRA AND OUTER SCALES

We have measured power spectra of atmospheric phase fluctuations with the Mark. III stellar interferometer on Mt. Wilson under a wide variet y of seeing conditions. On almost all nights, the high-frequency porti ons of the temporal power spectra closely follow the form predicted by the standard Kolmogorov-Tatarski model. At lower frequencies, a varie ty of behavior is observed. On a few nights, the spectra clearly exhib it the low-frequency flattening characteristic of turbulence with an o uter-scale length of the order of 30 m. On other nights, examination o f individual spectra yields no strong evidence of an outer scale less than a few kilometers in size, but comparison of the spectra on differ ent interferometer baselines shows a saturation of the spatial structu re function on long baselines. This saturation is consistent with the assumption of an outer-scale length similar to that derived for the ni ghts when low-frequency flattening of the spectra is clearly seen. We discuss possible explanations of this behavior and conclude that power spectra from a single interferometer baseline are a poor diagnostic f or the effective outer scale compared with multiple-baseline spectra.