The Rytov number is a fundamental scaling parameter for laser propagation through atmospheric turbulence. Rytov numbers greater than 0.2 are generally considered to be strong scintillation. A Rytov number of 0 would indicate no turbulence, thus no scintillation of the beam.
Physically, the Rytov number, or Rytov variance, is a measure of the strength of light scintillations—fluctuations in received irradiance, or in the phase and amplitude of the light, resulting from propagation through a turbulent space.