Spatial Representativeness of Surface‐Measured Variations of Downward Solar Radiation. Issue 24 (20th December 2017)

• Record Type: Journal Article
• Authors: Schwarz, M.; Folini, D.; Hakuba, M. Z.; Wild, M.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 24(2017)
• Page Start: 13, 319
• Page End: 13, 337
• Publication Date: 2017-12-20
• Subjects: spatiotemporal representativeness -- surface solar radiation; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2017JD027261
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: When using time series of ground‐based surface solar radiation (SSR) measurements in combination with gridded data, the spatial and temporal representativeness of the point observations must be considered. We use SSR data from surface observations and high‐resolution (0.05°) satellite‐derived data to infer the spatiotemporal representativeness of observations for monthly and longer time scales in Europe. The correlation analysis shows that the squared correlation coefficients ( R 2 ) between SSR times series decrease linearly with increasing distance between the surface observations. For deseasonalized monthly mean time series, R 2 ranges from 0.85 for distances up to 25 km between the stations to 0.25 at distances of 500 km. A decorrelation length (i.e., the e ‐folding distance of R 2 ) on the order of 400 km (with spread of 100–600 km) was found. R 2 from correlations between point observations and colocated grid box area means determined from satellite data were found to be 0.80 for a 1° grid. To quantify the error which arises when using a point observation as a surrogate for the area mean SSR of larger surroundings, we calculated a spatial sampling error (SSE) for a 1° grid of 8 (3) W/m 2 for monthly (annual) time series. The SSE based on a 1° grid, therefore, is of the same magnitude as the measurement uncertainty. The analysis generally reveals that monthly mean (or longer temporally aggregated) point observations of SSR capture the larger‐scale variability well. This finding shows that comparing time series of SSR measurements with gridded data is feasible for those time scales. Key Points: Point observations of variations in surface‐measured downward solar radiation are largely representative of their larger surroundings Correlations between sites decrease linearly with increasing distance Errors due to spatial sampling are of the same magnitude as measurement errors