Abstract
Abstract. A 1-year inter-comparison of classical and modern radiation and sunshine duration (SD) instruments has been performed at Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain) starting on 17 July 2014. We compare daily global solar radiation (GSRH) records measured with a Kipp & Zonen CM-21 pyranometer, taken in the framework of the Baseline Surface Radiation Network, with those measured with a multifilter rotating shadowband radiometer (MFRSR), a bimetallic pyranometer (PYR) and GSRH estimated from sunshine duration performed by a Campbell–Stokes sunshine recorder (CS) and a Kipp & Zonen sunshine duration sensor (CSD). Given that the BSRN GSRH records passed strict quality controls (based on principles of physical limits and comparison with the LibRadtran model), they have been used as reference in the inter-comparison study. We obtain an overall root mean square error (RMSE) of ∼ 0.9 MJm−2 (4 %) for PYR and MFRSR GSRH, 1.9 (7 %) and 1.2 MJm−2 (5 %) for CS and CSD GSRH, respectively. Factors such as temperature, relative humidity (RH) and the solar zenith angle (SZA) have been shown to moderately affect the GSRH observations. As an application of the methodology developed in this work, we have re-evaluated the GSRH data time series obtained at IZO with two PYRs between 1977 and 1991. Their high consistency and temporal stability have been proved by comparing with GSRH estimates obtained from SD observations. These results demonstrate that (1) the continuous-basis inter-comparison of different GSRH techniques offers important diagnostics for identifying inconsistencies between GSRH data records, and (2) the GSRH measurements performed with classical and more simple instruments are consistent with more modern techniques and, thus, valid to recover GSRH data time series and complete worldwide distributed GSRH data. The inter-comparison and quality assessment of these different techniques have allowed us to obtain a complete and consistent long-term global solar radiation series (1977–2015) at Izaña.
Highlights
The Earth’s radiation budget is essential for driving the general circulation of the atmosphere and oceans, and modulating the main conditions of the Earth’s climate system
We present the comparison of the daily GSRH values obtained with the different instruments and techniques using Baseline Surface Radiation Network (BSRN) as reference and we perform an analysis of the GSRH bias as a function of the season, solar irradiance, temperature, relative humidity (RH), fraction of clear sky (FCS) and aerosol optical depth (AOD)
As expected, the best agreements with BSRN GSRH are found for those instruments that directly measure solar radiation and have been calibrated with the LibRadtran model, since the model has been widely validated against the BSRN measurements at Izaña Atmospheric Observatory (IZO) (García et al, 2014b)
Summary
The Earth’s radiation budget is essential for driving the general circulation of the atmosphere and oceans, and modulating the main conditions of the Earth’s climate system. What we propose in this study is to know the performance of different instruments running in parallel in a test-bed site where the environmental conditions show a wide range of variation throughout the year This allows us to obtain comprehensive and consistent assessments on the GSRH differences obtained with these instruments. In this context, this work compares simultaneous groundbased GSRH measurements performed by different instruments with GSRH derived from SD and PYR area measurements in order to (1) document the traceability of main solar radiation techniques historically used, and thereby (2) assess their suitability for completing and recovering GSRH data time series, valid for climate studies.
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