Would Adaptive Optics be Useful in Radio Astronomy? This Question and Answer got me thinking. If atmospheric seeing at visible wavelengths is the result of refractive index inhomogeneity, would it also be a similar problem for mm to cm wavelengths? From a quick search, the index of refraction of air at STP is about 1.0003 (visible) and 1.0002 (radio).
If it is not, is there a way to understand quantitatively why it is not a problem?
 
Sources: 1, 2
In fact, the techniques of adaptive optics are already being used in radio astronomy.  They are implicit in the basic imaging algorithms (e.g., CLEAN) used to produce maps from radio interferometers.  In those cases, they are usually being used to correct for the artificial structure introduced by the way the interferometer samples the sky, rather than for structure imposed by the intervening material.  But at low frequencies (1 GHz and below, certainly) they are also used to correct for the artificial structure imposed on the incoming radio wavefronts as they pass through the ionosphere.  Current large low-frequency instruments (such as the LWA and LOFAR) rely heavily on these methods.