Abstract
For the first time Lévy indices (γ) of the solar light transmitted by cloudy skies at mid latitude (50°N, 8.2°E) are reported. The Lévy index describes the dependence of the mean geometrical paths (< LT > ) of photons transmitted from cloudy skies as a function of the vertical cloud extension (Hc) expressed by the scaling law <LT > ∼ Hcγ. For a set of 33 individual cloudy sky < LT > measurements, reported cloud types and heights, Lévy indices are deduced. It is found that the inferred Lévy indices cluster into the range of 1 ≤ γ ≤ 2 for “all sky” observations, and into a range 1.5 ≤ γ ≤ 2 for optically very thick clouds. The observations provide evidence that the cloudy sky geometrical path lengths are Lévy distributed with the γ value depending on the cloud morphology (the shape of individual clouds and the spatial arrangement of the clouds) but also on the internal cloud inhomogeneities. Because of a particular sensitivity of our method to detect the radiative transfer (RT) caused by clouds (rather than by the clear sky parts of the atmosphere), the inferred type of the path statistics is expected to reflect mostly the path length distribution caused by cloud inhomogeneities rather than by the cloud morphology. Since the cloud inhomogeneities are caused by dynamic processes (besides other factors), the RT transfer is expected to be closely connected to atmospheric dynamics. From this it is concluded that the absorption of solar radiation in cloudy skies is connected to the dynamic state (whether it is stratified or convective) of the cloud cover. In particular, it is expected to be different (mostly larger) than calculated by naively assuming homogeneous horizontally infinite cloud covers in conventional non statistical RT models.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.