  Numerical simulation is used to analyze statistical characteristics of vortex
beams propagating in the atmosphere. The cumulative distribution function and
the probability density function of intensity fluctuations are compared for
Gaussian beams and vortex beams. It is shown that for propagation conditions in
the turbulent atmosphere corresponding to weak fluctuations (Rytov parameter
much smaller than unity), intensity fluctuations at the axis of the Gaussian
beam have the lognormal distribution, whereas the probability density
distribution of the radiation intensity fluctuations at the axis of the vortex
beams is well approximated by the exponential distribution characteristic of
conditions of saturated fluctuations (Rytov parameter much larger than unity)
