Humidity's influence on visible region refractive index structure   parameter $C_n^2$
  In the infrared and visible bandpass, optical propagation theory conventionally assumes that humidity does not contribute to the effects of atmospheric turbulence on optical beams. While this assumption may be reasonable for dry locations, we demonstrate in this paper that there is an unequivocal effect due to the pre sence of humidity upon the strength of turbulence parameter, $C_n^2$, from data collected in the Chesapeake Bay area over 100-m length horizontal propagation paths. We describe and apply a novel technique, Hilbert Phase Analysis, to the relative humidity, temperature and $C_n^2$ data to show the contribution of the re levant climate variable to $C_n^2$ as a function of time. 
Mark P. J. L. Chang, Carlos O. Font, G. Charmaine Gilbreath and Eun Oh