The Saudi Arabian's Sky III The Clear sky Emissivity over Saudi Arabia

摘要

We present in this paper our third study in a series dealing with the sky of Saudi Arabia (Al-Mostafa & Maghrabi 2001a,b). The clear sky emissivity (ε{sub}o) for 23 stations around the Kingdom of Saudi Arabia has been calculated using Martin and Berdahl model (1984). This study shows that the values of the clear sky emissivity in Saudi Arabia were in the range 0.70-0.85 with an annual average 0.765±0.050. The maximum and minimum values of the emissivity were mainly in the summer and winter respectively. Riyadh and Qaisumah stations show the same trend with maximum and minimum values in April and November respectively. The long-term records of the clear sky emissivity show a sharp increase in the values of emissivity either in 1997 or 1998 for 8 and 7 stations respectively. Correlation between the clear sky emissivity and some meteorological parameters such as vapor pressure, dewpoint temperature and humidity has been investigated. While all stations show strong correlation with vapor pressure, four stations have strong correlation with dewpoint temperature and one with the humidity. Alwajh station is the only station that shows strong correlation between clear sky emissivity and the three meteorological parameters. This study will give us a further knowledge about the Saudi Arabian Sky, which will help astronomical site selections as well as benefit future solar energy studies and applications.