Humidity contribution to the refractive index structure function C_n^2

Humidity and C_n^2 data collected from the Chesapeake Bay area during the 2003/2004 period have been analyzed. We demonstrate that there is an unequivocal correlation between the data during the same time periods, in the absence of solar insolation. This correlation manifests itself as an inverse relationship. We suggest that C_n^2 in the infrared region is also function of humidity, in addition to temperature and pressure.