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

Harry D Kambezidis,Basil E Psiloglou

doi:10.3390/app10114043

Abstract

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 (TL) and the Unsworth–Monteith turbidity coefficient (TUM). 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 (k’t) is made, while a suggestion for a modified diffuse fraction (k’d) is given. The adoption of the four climatic zones in Greece for energy purposes is made, where the variation of TL and TUM 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 TL and TUM values over Greece show persistent minimum values over Peloponnese and maximum values over South Ionian Sea. Linear expressions of TUM vs. TL are derived for all sites under all and clear-sky conditions. Finally, linear expressions for k’d vs. k’t are given for all sites and sky conditions.

Highlights

Solar radiation reaching the surface of the Earth undergoes attenuation due to the absorption and scattering of the solar rays by the atmospheric constituents [1]
Empirical–analytical expressions have been provided in the international literature for the atmospheric transmittances of the first four constituents, such expressions would not have been possible for aerosols if the notion of atmospheric turbidity were not introduced
Where Be is the direct horizontal solar radiation equal to Ge - De, S is the correction factor for the Sun–Earth distance [29] given by Equation (3), Ge,o is the solar constant equal to 1361.10 Wm−2 [30], γ is the solar elevation, m’ is the pressure-corrected optical air mass (Equation (5)), which includes the altitude of the site at which the Linke (TL) is to be estimated, and kr is the mean attenuation of the direct solar radiation due to Rayleigh scattering alone [31,32]

Summary

Introduction

Solar radiation reaching the surface of the Earth undergoes attenuation due to the absorption and scattering of the solar rays by the atmospheric constituents [1]. The solar radiation levels measured on the surface of the Earth depend on the concentration of water vapor, nitrogen dioxide, ozone, mixed gases and atmospheric aerosols. Empirical–analytical expressions have been provided in the international literature for the atmospheric transmittances of the first four constituents, such expressions would not have been possible for aerosols if the notion of atmospheric turbidity were not introduced. The atmospheric turbidity expresses the attenuation of solar rays by aerosols.

Methods

Results

Conclusion