Spectral optical atmospheric thickness dependence on the specific humidity in the presence of continental and maritime air masses

Atmospheric and spectral solar irradiation data, measured at the Atmospheric Physics Laboratory of the University of Patras (38°17′N, 21°47′E, 64 m a.s.l.), are used to determine the water vapor dependence of the spectral optical atmospheric thickness. The amount of the atmospheric water vapor is being described by the atmospheric specific humidity. The values of the spectral optical atmospheric thickness are being regressed with the simultaneous values of the atmospheric specific humidity and on the wavelength of the spectral solar irradiation, during the occurrence of continental and maritime air masses. The data analysis indicates the decrease of spectral optical atmospheric thickness with increase of the wavelength of the solar beam irradiation and, mainly, the major role of the amount of atmospheric water vapor on the spectral optical atmospheric thickness due to continental or maritime aerosols. The water vapor interaction with the particles of the insoluble continental dust results to the partial wetting and growing of the dust particles. In the atmospheric specific humidity minimum, which is observed in the dry and cold season, the spectral optical atmospheric thickness is minimized with the prevalence of continental air mass. In the atmospheric specific humidity maximum, which is observed in the wet and warm season, the spectral optical atmospheric thickness is maximized with the continental air mass prevalence, too. The water vapor interaction with the soluble sea-salt crystals of maritime aerosol is opposite from this with the insoluble continental dust and results in the complete dissolution of the sea-salt crystals in the wet season. During the presence of maritime air masses, the included sea-salt aerosols are dissolved by the atmospheric water vapor and the spectral optical atmospheric thickness takes intermediate values in the near violet and visible spectral regions of the solar spectrum. The observational data analysis results in two families of regression curves of the spectral optical atmospheric thickness with the atmospheric specific humidity, one corresponding to the continental and one to the maritime aerosol. The aim of this work is the explanation of the physical phenomenon of the hot sunrays during some winter days and of the weak sunrays during summer days.