Decadal variations in estimated surface solar radiation over Switzerland since the late 19th century Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
25 Sep 2012
Received: 27 Mar 2012 – Published in Atmos. Chem. Phys. Discuss.: 25 Apr 2012 Abstract. Our knowledge on trends in surface solar radiation (SSR) involves
uncertainties due to the scarcity of long-term time series of SSR,
especially with records before the second half of the 20th century.
Here we study the trends of all-sky SSR from 1885 to 2010 in Switzerland,
which have been estimated using a homogenous dataset of sunshine duration
series. This variable is shown to be a useful proxy data of all-sky SSR,
which can help to solve some of the current open issues in the
dimming/brightening phenomenon. All-sky SSR has been fairly stable with
little variations in the first half of the 20th century, unlike the
second half of the 20th century that is characterized also in
Switzerland by a dimming from the 1950s to the 1980s and a subsequent
brightening. Cloud cover changes seem to explain the major part of the
decadal variability observed in all-sky SSR, at least from 1885 to the
1970s; at this point, a discrepancy in the sign of the trend is visible in
the all-sky SSR and cloud cover series from the 1970s to the present.
Finally, an attempt to estimate SSR series for clear-sky conditions, based
also on sunshine duration records since the 1930s, has been made for the
first time. The mean clear-sky SSR series shows no relevant changes between
the 1930s to the 1950s, then a decrease, smaller than the observed in the
all-sky SSR, from the 1960s to 1970s, and ends with a strong increase from
the 1980s up to the present. During the three decades from 1981 to 2010 the
estimated clear-sky SSR trends reported in this study are in line with
previous findings over Switzerland based on direct radiative flux
measurements. Moreover, the signal of the El Chichón and Pinatubo
volcanic eruption visible in the estimated clear-sky SSR records further
demonstrates the potential to infer aerosol-induced radiation changes from
sunshine duration observations.
Revised: 14 Aug 2012 – Accepted: 07 Sep 2012 – Published: 25 Sep 2012
Citation: Sanchez-Lorenzo, A. and Wild, M.: Decadal variations in estimated surface solar radiation over Switzerland since the late 19th century, Atmos. Chem. Phys., 12, 8635-8644, doi:10.5194/acp-12-8635-2012, 2012.