1. Continued positive trend in surface solar radiation over Sweden
Thomas Carlund
Swedish Meteorological & Hydrological Institute, Norrköping, Sweden.
Vienna | Austria | 7–12 April 2019

2. Outline Brief overview of the Swedish solar radiation network
Time series of incoming solar radiation over Sweden
Time series of turbidity

3. The radiation network of SMHI
, the ”old” network
12 ”longterm” stations G, I, D and SD 6-minute means
Since 2007
3 ”advanced” stations G, I, D, L, AOD and SD, 1-minute mean and std.
14 ”simple” stations G, SD , 4 also incl. L 1-minute means
1 station with only SD
SMHI has participated at IPCs from the beginning. Good quality pyranometers, ventilated since the start. Overlapping measurements Calibration methods for pyranometers have changed over time, but the time series are considered as ”nearly” homogenous.
2 total ozone and UV stations

4. SMHI radiation station in Norrköping
Operational station
Reference and calibration station

5. Some ”long-term” solar radiation measurement results…

6. Annual mean global irradiance
Global radiation
Significant positive trend at all long-term stations to Wm-2/year
Increase in global irradiation during spring, summer and autumn
Record-high global irradiation 2018 at 11 of 12 long-term ( ) stations
Climate indicator G (8 stns)

7. 2018 sunniest year so far!
But. Sunshine duration series are not homogenous

8. Atmospheric dynamics Main cause of the record-sunny 2018 over Sweden…
Summer half year (apr-sep) geopotential height anomaly at 500 hPa. (Reference period )
From:
Fachbericht MeteoSchweiz Nr. 272 Hitze und Trockenheit im Sommerhalbjahr 2018 – eine klimatologische Übersicht

9. Global, direct and diffuse irradiance
The three ”advanced” radiation stations
Global Wm-2/year
Direct normal Wm-2/year
Direct horizontal Wm-2/year
Diffuse Wm-2/year

10. Longer-term global radiation time series now available
Report by Weine Josefsson,SMHI, available at
Or web search: Long-term global radiation Stockholm

11. Turbidity from direct irradiance
Annual means of Ångström’s turbidity coefficient , β
AODλ = βλ-α
β = AOD at 1000 nm
Calculated from 6-minute mens of direct irradiance measurements according to Gueymard (1998).
α = 1.3
Water vapour estimated from T and RH at 2-m.
Cloud screening: β-stability during 30 minute windows

12. One cause of increased solar radiation over Sweden…
Decreasing turbidity/AOD
Sunphotometer
Turbidity derived from pyrheliometer measurements
Ångström turbidity coefficient, β
Non-volcanic years: Linear trend = decade-1

13. Indications of decreasing cloudiness over Scandinavia (1984-2009)
Karlsson and Devasthale, 2018 (Remote Sensing).

14. Conclusions
Significant increasing trends in incoming solar radiation since 1980-ies over Sweden
Most of the increase happend 1983 to ~2005
The summer and summer half year of 2018 was extremely sunny and warm over Scandinavia
Probably as sunny or sunnier summers exiated before 1980-ies
Both decreases in aerosol load and cloudiness are thought to have contributed to the increase in surface solar radiation over Sweden

15. Thank you for your attention!
Kiruna