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L. J. Bruce McArthur
and
John E. Hay

Abstract

A technique to map the distribution of diffuse solar radiation over the sky hemisphere is described. The method is based on an analysis of all-sky, visible photographs and concurrent actinometric measurements of diffuse solar radiance. The photographs were digitized and the resulting relative density values correlated with directly measured radiances. The resulting relationship was then used to determine the radiance for each density value, enabling a map of diffuse solar radiation for the celestial dome to be constructed.

The validity and utility of the approach are assessed by several tests. In the first test, the estimated radiances were integrated over the hemisphere and compared with measured diffuse irradiances for a horizontal surface. These were found to be within ±10% for the variety of sky conditions examined. A second test, under clear sky conditions, was performed to estimate the shortwave irradiance on several south-facing inclined surfaces. The results were found to be within ±5% of the measured irradiances. In a third test, comparisons with the normalized radiance distributions of Steven (1977) indicated good qualitative agreement.

Finally, problems and deficiencies in the technique are reviewed and possible means of surmounting them are discussed.

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Rolf Philipona
,
Claus Fröhlich
,
Klaus Dehne
,
John DeLuisi
,
John Augustine
,
Ellsworth Dutton
,
Don Nelson
,
Bruce Forgan
,
Peter Novotny
,
John Hickey
,
Steven P. Love
,
Steven Bender
,
Bruce McArthur
,
Atsumu Ohmura
,
John H. Seymour
,
John S. Foot
,
Masataka Shiobara
,
Francisco P. J. Valero
, and
Anthony W. Strawa

Abstract

With the aim of improving the consistency of terrestrial and atmospheric longwave radiation measurements within the Baseline Surface Radiation Network, five Eppley Precision Infrared Radiometer (PIR) pyrgeometers and one modified Meteorological Research Flight (MRF) pyrgeometer were individually calibrated by 11 specialist laboratories. The round-robin experiment was conducted in a “blind” sense in that the participants had no knowledge of the results of others until the whole series of calibrations had ended. The responsivities C(μV/W m−2) determined by 6 of the 11 institutes were within about 2% of the median for all five PIR pyrgeometers. Among the six laboratories, the absolute deviation around the median of the deviations of the five instruments is less than 1%. This small scatter suggests that PIR pyrgeometers were stable at least during the two years of the experiment and that the six different calibration devices reproduce the responsivity C of PIR pyrgeometers consistently and within the precision required for climate applications. The results also suggest that the responsivity C can be determined without simultaneous determination of the dome correction factor k, if the temperature difference between pyrgeometer body and dome is negligible during calibration. For field measurements, however, k has to be precisely known. The calibration of the MRF pyrgeometer, although not performed by all institutes, also showed satisfactory results.

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Taneil Uttal
,
Sandra Starkweather
,
James R. Drummond
,
Timo Vihma
,
Alexander P. Makshtas
,
Lisa S. Darby
,
John F. Burkhart
,
Christopher J. Cox
,
Lauren N. Schmeisser
,
Thomas Haiden
,
Marion Maturilli
,
Matthew D. Shupe
,
Gijs De Boer
,
Auromeet Saha
,
Andrey A. Grachev
,
Sara M. Crepinsek
,
Lori Bruhwiler
,
Barry Goodison
,
Bruce McArthur
,
Von P. Walden
,
Edward J. Dlugokencky
,
P. Ola G. Persson
,
Glen Lesins
,
Tuomas Laurila
,
John A. Ogren
,
Robert Stone
,
Charles N. Long
,
Sangeeta Sharma
,
Andreas Massling
,
David D. Turner
,
Diane M. Stanitski
,
Eija Asmi
,
Mika Aurela
,
Henrik Skov
,
Konstantinos Eleftheriadis
,
Aki Virkkula
,
Andrew Platt
,
Eirik J. Førland
,
Yoshihiro Iijima
,
Ingeborg E. Nielsen
,
Michael H. Bergin
,
Lauren Candlish
,
Nikita S. Zimov
,
Sergey A. Zimov
,
Norman T. O’Neill
,
Pierre F. Fogal
,
Rigel Kivi
,
Elena A. Konopleva-Akish
,
Johannes Verlinde
,
Vasily Y. Kustov
,
Brian Vasel
,
Viktor M. Ivakhov
,
Yrjö Viisanen
, and
Janet M. Intrieri

Abstract

International Arctic Systems for Observing the Atmosphere (IASOA) activities and partnerships were initiated as a part of the 2007–09 International Polar Year (IPY) and are expected to continue for many decades as a legacy program. The IASOA focus is on coordinating intensive measurements of the Arctic atmosphere collected in the United States, Canada, Russia, Norway, Finland, and Greenland to create synthesis science that leads to an understanding of why and not just how the Arctic atmosphere is evolving. The IASOA premise is that there are limitations with Arctic modeling and satellite observations that can only be addressed with boots-on-the-ground, in situ observations and that the potential of combining individual station and network measurements into an integrated observing system is tremendous. The IASOA vision is that by further integrating with other network observing programs focusing on hydrology, glaciology, oceanography, terrestrial, and biological systems it will be possible to understand the mechanisms of the entire Arctic system, perhaps well enough for humans to mitigate undesirable variations and adapt to inevitable change.

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