Climatology of the Linke and Unsworth–Monteith Turbidity Parameters for Greece: Introduction to the Notion of a Typical Atmospheric Turbidity Year

• Main Authors: Harry D. Kambezidis, Basil E. Psiloglou
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Applied Sciences
• Subjects: atmospheric turbidity; Linke turbidity factor; Unsworth–Monteith turbidity coefficient; Typical Atmospheric Turbidity Year; modified clearness index; modified diffuse fraction
• Online Access: https://www.mdpi.com/2076-3417/10/11/4043

Solar rays are attenuated by the Earth’s atmosphere. This attenuation can be expressed by the turbidity parameters; two of them are the Linke turbidity factor (<i>T</i>_L) and the Unsworth–Monteith turbidity coefficient (<i>T</i>_UM). In this sudy, both parameters are estimated for 33 sites across Greece, and the notion of a Typical Atmospheric Turbidity Year (TATY) is also introduced. Use of the modified clearness index (<i>k</i>’_t) is made, while a suggestion for a modified diffuse fraction (<i>k</i>’_d) is given. The adoption of the four climatic zones in Greece for energy purposes is made, where the variation of <i>T</i>_L and <i>T</i>_UM is studied during a TATY under all and clear-sky conditions. The analysis shows maximum levels in both parameters in late winter–early spring in morning and evening hours, with minimum values at midday. The intra-annual variation of the parameters shows maximum values around March and August and minimum values in summertime and late winter. Maps of annual mean <i>T</i>_L and <i>T</i>_UM values over Greece show persistent minimum values over Peloponnese and maximum values over South Ionian Sea. Linear expressions of <i>T</i>_UM vs. <i>T</i>_L are derived for all sites under all and clear-sky conditions. Finally, linear expressions for <i>k</i>’_d vs. <i>k</i>’_t are given for all sites and sky conditions.