Estimation of atmospheric turbidity over Ghardaïa city

• Five years of solar irradiance and meteorological parameters are used to investigate the turbidity over Ghardaïa city.
• Two parameters are used, the Linke factor and the Angström coefficient.
• The monthly average value varied between 1.34 and 5.58 for the Linke factor and between 0.02 and 0.19 for Angström coefficient.
• A total of 47.5% of the Linke factor values were between 3 and 5.
• A total of 75.4% of Angström coefficient values were between 0.02 and 0.15.

The atmospheric turbidity expresses the attenuation of the solar radiation that reaches the Earth's surface under cloudless sky and describes the optical thickness of the atmosphere. We investigate the atmospheric turbidity over Ghardaïa city using two turbidity parameters, the Linke turbidity factor and the Angström turbidity coefficient. Their values and temporal variation are obtained from data recorded between 2004 and 2008 at Ghardaïa. The results show that both parameters have the same trend along the year. They reach their maximum around summer months and their minimum around winter months. The monthly average value varies between 1.3 and 5.6 for the Linke turbidity factor and between 0.02 and 0.19 for the Angström turbidity coefficient. We find that 39.8% of the Linke turbidity factor values are less than 3, 47.5% are between 3 and 5 and only 12.7% are greater than 5. For the Angström turbidity coefficient, 9.4% of the values are less than 0.02, 75.4% are between 0.02 and 0.15 and 15.2% exceed 0.15.