Reconstruction of global solar radiation time series from 1933 to 2013 at the Izaña Atmospheric Observatory

Abstract

Abstract. This paper presents the reconstruction of the 80-year time series of daily global solar radiation (GSR) at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (The Canary Islands, Spain). For this purpose, we combine GSR estimates from sunshine duration (SD) data using the Ångström-Prescott method over the 1933/1991 period, and GSR observations directly performed by pyranometers between 1992 and 2013. Since GSR measurements have been used as a reference, a strict quality control has been applied based on principles of physical limits and comparison with LibRadtran model. By comparing with high quality GSR measurements, the precision and consistency over time of GSR estimations from SD data have been successfully documented. We obtain an overall root mean square error (RMSE) of 9.2 % and an agreement between the variances of GSR estimations and GSR measurements within 92 %. Nonetheless, this agreement significantly increases when the GSR estimation is done considering different daily fractions of clear sky (FCS). In that case, RMSE is reduced by half, to about 4.5 %, when considering percentages of FCS > 40 % (∼ 90 % of days in the testing period). Furthermore, we prove that the GSR estimations can monitor the GSR anomalies in consistency with GSR measurements and, then, can be suitable for reconstructing solar radiation time series. The reconstructed IZO GSR time series between 1933 and 2013 confirms change points and periods of increases/decreases of solar radiation at Earth's surface observed at a global scale, such as the early brightening, dimming and brightening. This fact supports the consistency of the IZO GSR time series presented in this work, which may be a reference for solar radiation studies in the subtropical North Atlantic region.

Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

“…In the last decades, numerous analyses have demonstrated that SSR records have not been constant over time, but have undergone climatologically significant decadal variations (e.g. Pallé and Butler, 2001;Stanhill and Cohen, 2001;Sanchez-Lorenzo et al, 2007;Wild, 2009;García et al, 2014a). From the 1930s to the early 1950s the few data available suggest an increase of the SSR in the first part of the 20th century, known as early brightening.…”

“…Firstly, AOD estimations were conducted using the measured values for all parameters described in the previous section, obtaining the non-perturbed values (AOD). Secondly, the same sample was simulated again by applying the typical uncertainties of the inputs parameters reported in the literature, ±5 % for FCS (García et al, 2014a) and ±2 % for RH (Thies, 2011). For the horizontal visibility we have assumed a very conservative error of ±25 %.…”

“…To minimize the latter impacts on the variability of the VIS, we only work with cloud-free days filtered with an average sky cover of 0 oktas. Furthermore, we have introduced the fraction of clear sky (FCS) defined as the ratio between SD performed with a Campbell Stokes sunshine recorder (García et al, 2014a) and the maximum daily sunshine duration SD max to account for the remaining variability introduced by the presence of clouds, fog, etc. The introduction of FCS in the ANN training allows the ANN to discriminate the patterns associated with possible residual cloud cover for the days with oktas = 0.…”

“…This effect, extensively reported by the literature at a global scale, is known as dimming, with a general decline between 4 and 6 % decade −1 considering worldwide distributed stations. Recently, a gradual increase of the SSR has been documented, known as brightening, with trends between +1 and +11 % decade −1 from the 1980s onwards (Ohmura and Lang, 1989;De Bruin et al, 1995;Gilgen et al, 1998;Stanhill and Cohen, 2001;Ohmura, 2006;Wild et al, 2005;Sanchez-Lorenzo et al, 2007;Wild et al, 2008;Wild, 2009;Lachat and Wehrli , 2013;García et al, 2014a).…”

Compatibility of different measurement techniques of global solar radiation and application for long-term observations at Izaña Observatory

“…The SD has been widely used by applying the wellknown Ångström-Prescott equation (Angstrom, 1924(Angstrom, , 1956Prescott, 1940) to estimate GSR H . Several authors, such as Almorox et al (2005), Yorukoglu and Celik (2006) and García et al (2014b), have used this method in different regions, obtaining similar results. The Robitzsch bimetallic pyranometer (also know as pyranograph or actnigraph, hereafter PYR), designed in the early 1920s (Robitzsch, 1926) and widely used until the late 1960s, measures GSR H from an equation involving the recorded area and the ambient temperature (Robitzsch, 1932).…”