Authors: Costas A Varotsos Irina Melnikova Maria N Efstathiou Chris Tzanis
Publish Date: 2012/06/27
Volume: 111, Issue: 3-4, Pages: 641-648
Abstract
The investigation of the intrinsic properties of the solar spectral irradiance as a function of the ultraviolet UV wavelength is attempted by exploiting rare observations performed at the Villard St Pancrace station of the Lille University of Sciences and Technology ranging from 278 to 400 nm with a step of 005 nm every half an hour from nearly sunrise to sunset To achieve this goal the modern method of the detrended fluctuation analysis was applied on the solar spectral irradiance values versus wavelength This analysis revealed that the solar incident flux at the top of the atmosphere and the solar spectral irradiance at the ground during two overcast sky days fluctuate with the UV wavelength exhibiting persistent longrange powerlaw behavior More interestingly the exponent of the powerlaw relationship between the fluctuations of the solar spectral irradiance versus UV wavelength at both the top of the atmosphere and the ground is consistently close to unity of 1/ftype throughout the day This 1/f behavior has been detected in many complex dynamical systems but despite much effort to derive a theory for its widespread occurrence in nature it remains unexplained so far According to the abovementioned findings we speculate that the 1/f property of the incident solar UV flux at the top of the atmosphere could probably drive both the 1/f behavior depicted in the atmospheric components and the solar UV irradiance at the Earths surface The latter could influence the UVsensitive biological ecosystems giving rise to a 1/ftype variability in the biosphere which has already been proven by recent observational data We finally propose that Wien approximation could be multiplied by a 1/f function of wavelength eg of the type of the fractional Brownian motion in order to reproduce the aforementioned 1/f feature of the solar UV flux
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