Many studies were dedicated to the analysis of the propagation of High Energy Laser beams in free space. Laser beams propagation performance in the presence of atmospheric constituents may degrade by some interrelated linear and nonlinear phenomena. In this study, it is proposed a self-contained model including non-linear air temperature effect producing thermal distortion in laser propagation. In order to better understand the underlying phenomena, a set of quantifiers are described leading to the characterization of the laser thermal distortion. A parametric study is finally proposed in order to highlight the influence of the different parameters of the simulations.