Remote sensing of cirrus clouds and aerosols by a sun photometer in Tunisia

Abstract. Some ground based measurements of solar radiation by using a sun photometer, have been conducted in Tunisia during the period of November 2000–February 2002. Five key measurement sites were selected: Three Sites (Tunis, Sousse, Gabes) are located on the Mediterranean coast and Two sites (Gafsa, Tozeur) on the boarder of Sahara. Over a total of 149 measurement days, 21 days are identified as clear sky, 114 days as Cirrus clouds and 14 days as aerosols.

Aerosols and Cirrus clouds Optical Thickness (AOT) are derived from photometric measurements at 532 nm wavelength. Spatial and temporal variabilities of AOT are presented and discussed in this paper.

Cirrus clouds were frequently observed at Gafsa and Tozeur where saharan aerosol events are expected to be more frequent than cirrus clouds. The mediterranean sea and saharan aerosols are suspected to have the main role in cirrus clouds formation, by providing water vapor and high concentrations of cloud condensation and ice forming nuclei.