Optical Turbulence (OT) is a phenomenon in which wavefronts from celestial bodies are perturbed when passing through our atmosphere, due to small fluctuations in the atmosphere’s refractive index .
These fluctuations arise due to wind shear and thermally stable stratification of the atmosphere.
The effect of the perturbation of the wavefronts is a lower resolution in ground-based observations, quantified by the metric known as seeing. Due to this lower resolution, point sources of light have an apparent angular diameter when observed through the atmosphere.
OT is most intense near sea level, followed by a second spike near the jet-stream.
The issues presented by OT can be addressed via the use of Adaptive Optics.
 Hagelin, S., Masciadri, E. and Lascaux, F. Optical Turbulence The influence of the atmosphere on ground-based astronomy. 1.