The Use of Weather Forecasts to Characterise Near-Surface Optical Turbulence

Abstract

The propagation of optical and electromagnetic waves is affected by small-scale atmospheric turbulence, quantified by the structure parameter of the refractive index. In the atmospheric surface layer, the mean structure parameter C2n, as averaged over the large-scale turbulence, relates to meteorological forcings through well-documented relationships. Present-day numerical weather forecast models routinely produce these forcings at the global scale. This study introduces a method where the products of such a model are used to calculate the mean optical turbulence near the surface. The method is evaluated against scintillometry measurements over climatologically distinct sites in Western Europe. The diurnal cycle modulation, and regional and seasonal contrasts, are all reproduced by our predictions. Hence, the present method explains and predicts some essential aspects of the meteorological variability of 2n near the surface. The noted discrepancies combine instrumental limitations, site peculiarities, differences related to distinct averaging procedures, and model errors, notably from weather forecasts. The minute-scale fluctuations of the measured scintillation rate are also analysed in the light of the forecast weather conditions. Fair-weather daytime periods consistently show a small short-term variability compared to the nighttime and perturbed weather periods. Thus, this short-term variability appears to have a predictable component

Long-term, global-scale statistics of sound propagation

“…The use of MOST is consistent with that formulation. Cheinet et al (2011) demonstrate that the turbulence diagnostics obtained with this approach are consistent with measurements in the surface layer.…”

“…The database is described in Cheinet et al (2011). It is obtained with the NWP model of the European Center for Medium Range Weather Forecasts (ECMWFs).…”

“…In the atmospheric surface layer, the Monin-Obukhov Similarity Theory (MOST) offers a welldocumented framework to consistently derive stratification and turbulence from standard NWP systems (Cheinet et al, 2011). The present study couples this NWP-based atmospheric parameterization to the sound propagation model of C12, in order to reveal the variability of the sound propagation over long-term and global scales.…”

Effects of Non-Uniform Crosswind Fields on Scintillometry Measurements

“…4.4), the theoretical spectra have been normalized to the observational spectra using the 5-min value of C 2 n . Assuming a constant C 2 n over the 5-min interval was judged more appropriate than calculating individual C 2 n values for every 10-s sub-interval (Cheinet et al 2011). When studying spectra for longer periods the change in C 2 n with time could be included.…”

Variational Multiscale based dissipation models for the estimation of atmospheric seeing

“…Soon after, the same methodology was applied to the simulation of another observation site at the Roque de Los Muchachos, Canary Islands, Spain [31]. In [7,8,6] a Large Eddy Simulation (LES) model run on a weather forecast simulation software was used to characterize near-surface optical turbulence under different climatic conditions in observation sites. A seeing model which makes use of the turbulent kinetic energy provided by a planetary boundary layer simulation software was used to compute seeing in Mauna Kea, Hawaii in [10,9].…”