Abstract
Abstract. A large number of radiometers are traceable to the World Standard Group (WSG) for shortwave radiation and the interim World Infrared Standard Group (WISG) for longwave radiation, hosted by the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC, Davos, Switzerland). The WSG and WISG have recently been found to over- and underestimate radiation values, respectively (Fehlmann et al., 2012; Gröbner et al., 2014), although research is still ongoing. In view of a possible revision of the reference scales of both standard groups, this study discusses the methods involved and the implications on existing archives of radiation time series, such as the Baseline Surface Radiation Network (BSRN). Based on PMOD/WRC calibration archives and BSRN data archives, the downward longwave radiation (DLR) time series over the 2006–2015 period were analysed at four stations (polar and mid-latitude locations). DLR was found to increase by up to 3.5 and 5.4 W m−2 for all-sky and clear-sky conditions, respectively, after applying a WISG reference scale correction and a minor correction for the dependence of pyrgeometer sensitivity on atmospheric integrated water vapour content. Similar increases in DLR may be expected at other BSRN stations. Based on our analysis, a number of recommendations are made for future studies.
Highlights
In order to ensure the worldwide homogeneity and calibration of radiation measurements, the World Radiation Centre at the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC) in Davos (DAV; 46.8143◦ N, 9.8458◦ E, 1580 m above sea level; Switzerland) was established on behalf of the World Meteorological Organization (WMO)
Based on PMOD/WRC calibration archives and Baseline Surface Radiation Network (BSRN) data archives, the downward longwave radiation (DLR) time series over the 2006–2015 period were analysed at four stations
This section discusses the results from an analysis of shortand longwave radiometers in the PMOD/WRC and BSRN archives
Summary
In order to ensure the worldwide homogeneity and calibration of radiation measurements, the World Radiation Centre at the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC) in Davos (DAV; 46.8143◦ N, 9.8458◦ E, 1580 m above sea level; Switzerland) was established on behalf of the World Meteorological Organization (WMO). The World Standard Group (WSG) of pyrheliometers was used to establish the World Radiometric Reference (WRR) in 1970 and represents the SI unit of radiation for the shortwave range. The latter is broadly defined as covering the wavelength range ∼ 0.3– 3 μm (Petty, 2006), while the WSG pyrheliometers cover the range from less than 0.2 to above 50 μm (Reda et al, 2017). Longwave radiation is broadly defined as covering the ∼ 4–100 μm range (Petty, 2006), while the WISG pyrgeometers cover the range ∼ 4–50 μm (Eppley Precision Infrared Radiometer (PIR) pyrgeometers) and ∼ 4.5–42 μm (Kipp & Zonen CG(R) pyrgeometers). Recent measurements with newly developed high-precision ground-based radiometers have demonstrated that a revision of approximately −0.3 % and up to +5 W m−2 of the WSG and WISG scales, respectively, may be required
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