Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Comparison of some instruments and methods for determination of sunshine duration Thomas Carlund Swedish Meteorological & Hydrological Institute, SMHI. From tenths of percent to tens of percent… IPC-X 26/9 – 14/ , PMOD/WRC Davos, Switzerland.

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Compared instruments and methods • Pyrheliometers:K&Z CH1 – Reference Eppley NIP Forgan 1-min statistics method • Sunshine sensors: K&Z CSD2 Campbell-Stokes (Fuess) heliograph • Pyranometer (CM21): Olivieri method (WMO, 1998) MSC method

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Measurement period: – Place: SMHI, Norrköping (58.58 °N, °E). Time resolution Direct beam instr: Instantaneous every 3 s. Pyranometers: 1-minute mean global irradiance SD(Forgan)= ∑(E b,min >120) + A*(∑(E b,min 120)) + B Constraints • CH1 and NIP on different trackers. The NIP ‘s tracker is less accurate. •MSC-method - SMARTS2 for clear sky calculations instead of Davies and Hay. - Water vapour from HIRLAM instead of 2-m temperature and humidity. • Heliograph data only from working days.

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Calibration of CSD2 The CSD2 has an analog output, aproximating the direct irradiance. SD(CH1)= 6.8 h, SD(CSD2)= 9.4 h Direct = Good, Sun Dur = Good Direct = Bad, Sun Dur = Good Direct = Bad, Sun Dur = Bad

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Cont. Calibration of CSD2 Clear sky calibration 1 hour around solar noon with declination correction most reproducible

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Cont. Calibration of CSD2 E b (CSD2)= C*V(CSD2A) – Offset [Wm -2 ] Offset = (-) 65 Wm -2

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Cont. Calibration of CSD2 CSD2 calibration is sensitive to brightness of (back-)ground But offset remained the same.

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Calibration factors for several CSD1s and CSD2s.

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Results

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer

But… J. Olivieri’s method is based on 1-minute mean values of direct irradiance to derive sunshine duration. The MSC method was developed to agree with Canadian Campbell-Stokes data on sunshine duration. And the latest version of this method was not used.

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Summary

Mellanblå fält till höger: Plats för bild – foto, diagram, film, andra illustrationer Conclusions • Pyrheliometer methods – High precision and accuracy Close to 0.1 h uncertainty or better in daily totals (level of confidence 95 %) • Standard K&Z CSD2 appear to measure too much sunshine dur • By applying gain and offset to the CSD2 output its results can be significantly improved. On-site calibration preferable. • Investigated pyranometer methods need to be modified to give average results comparable to correct pyrheliometer results • Campbell-Stokes - Largest scatter