Atmospheric Longwave Irradiance Uncertainty
Philipona, R. (a), Dutton, E.G. (b), Wood, N. (b), Anderson, G. (b), Stoffel, T. (c), Reda, I. (c), Michalsky, J.J. (d), Wendling, P. (e), Stiffter, A. (e), Clough, S.A. (f), Mlawer, E.J. (f), Revercomb, H. (g), and Shippert, T. (h), World Radiation Center, Davos, Switzerland (a), NOAA, Climate Monitoring and Diagnosic Laboratory (b), National Renewable Energy Laboratory (c), State University of New York at Albany (d), DLR, Oberfaffenhofen, Germany (e), Atmospheric and Environmental Research Inc. (f), University of Wisconsin-Madison (g), Pacific Northwest National Laboratory (h)
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting
The first International Pyrgeometer and Absolute Sky-scanning Radiometer Comparison (IPASRC-I), which was held in fall 1999 at the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) site in Oklahoma, shows astonishingly good agreement between downward longwave radiation measurements and calculations of different instruments and radiative transfer models. The difference, averaged over four nighttime cases, between the Absolute Sky-scanning Radiometer (ASR) and pyrgeometers, AERI, LBLRTM and MODTRAN is less than 2 Wm-2. This result boosts confidence in the correctness of present day clear-sky nighttime longwave irradiance measurements and calculations, indicating that absolute uncertainty levels as low as ± 1.5 Wm-2 or 0.5 percent are practicable and realistic, at least for mid-latitude summer conditions. The ASR was used as a reference standard instrument to field calibrate pyrgeometers which produced remarkable improvements in pyrgeometer precision compared to standard blackbody calibrations. IPASRC-I demonstrates that state-of-the-art pyrgeometers are "Precision Infrared Radiometers" (PIRs) if they are correctly calibrated and deployed. A second IPASRC campaign is planed to investigate longwave radiation under arctic winter conditions at the ARM, CART site in Barrow in early 2001.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
