Shortwave Radiometry and Analysis at the Southern Great Plains (SGP) Site (original) (raw)
Related papers
Journal of the Atmospheric Sciences, 1997
This study presents surface solar radiation flux and cloud radiative forcing results obtained by using a combination of satellite and surface observations interpreted by means of a simple plane-parallel radiative transfer model called 2001. This model, a revised version of a model initially introduced by Gautier et al., relates calibrated radiance observations from space to incoming surface solar flux. After a description of the model, an evaluation is presented by comparison with a more complex model that the authors have developed, the Santa Barbara DISORT Atmospheric Radiative Transfer model (SBDART) based on the discrete ordinate model of Stamnes et al. This evaluation demonstrates this model's accuracy for instantaneous surface flux when used to retrieve daily (and monthly) surface solar flux. Limitations related to its lack of treatment of the bidirectional reflectance properties of clouds are also discussed and quantified by comparison with SBDART for instantaneous surface solar flux retrievals. The influence of satellite sensor calibration uncertainty is also examined in terms of surface solar flux. The model has been applied to hourly GOES data collected over the Atmospheric Radiation Measurement (ARM) program's central cloud and radiation testbed site in Oklahoma during a 14-month period to estimate hourly, daily, and monthly surface solar radiation flux. Comparisons of the model's results with surface measurements made from pyranometers located at the ARM site indicate good overall agreement. The best results are obtained for daily integrated clear skies with an rms error less than 10 W m Ϫ2 (or about 3% of the mean value) and a 2.8 W m Ϫ2 bias. These results indicate that the clear sky model is quite accurate and also that the threshold-based technique to detect cloudy conditions works well for the resolution of the satellite data used in this study. For partly cloudy conditions the comparisons show an rms error of about 20 W m Ϫ2 (or less than 7% of the mean) and a Ϫ2.5 W m Ϫ2 bias. The performance of the model degrades with cloud cover conditions with an rms error of 22 W m Ϫ2 (or 13% of the mean) and a bias of 13.9 W m Ϫ2 for overcast conditions. The results improve considerably for monthly average values with an rms error of about 11 W m Ϫ2 (or 4% of the mean) and a bias of 2.6 W m Ϫ2 for all conditions. The model has also been used to evaluate the cloud radiative forcing at the surface and results indicate large values of forcing for the spring and summer reaching daily values over 200 W m Ϫ2 in May.
Sun and Sky Radiometric Measurements at the CART ARM SGP Site
1999
Cimel sunphotometers/radiometers (CSPHOT) are facility instruments at the three Atmospheric Radiation Measurement (ARM) sites at the Southern Great Plains (SGP) in Oklahoma, Tropical Western Pacific (TWP) in Nauru, and North Slope in Alaska (NSA). Here inferred aerosol optical thickness (AOT) and precipitable water (PW) measurements at the SGP site are compared with measurements using other instruments. Aerosol size distribution derived from direct solar measurements and from the aureole sky brightness measurements are also compared. Results show that the quality of the measurements is high, suitable for modeling of other radiation quantities.
Results from the first ARM diffuse horizontal shortwave irradiance comparison
Journal of Geophysical Research, 2003
1] The first intensive observation period (IOP) dedicated exclusively to the measurement of diffuse horizontal shortwave irradiance was held in the Fall 2001 at the central facility of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site with the cooperation of the Baseline Surface Radiation Network (BSRN) community. The purpose of the study was to compare diffuse irradiance measurements among most commercial pyranometers and a few prototypes calibrated independently using current practices. The hope was to achieve a consensus for this measurement with the goal of improving the uncertainty of shortwave diffuse irradiance measurements. All diffuse broadband measurements were made using the same type of two-axis tracker with the direct beam blocked by shading balls. Tracking was excellent during the IOP with no lost data associated with tracker problems. Fourteen simultaneous measurements were obtained over a two-week period under mostly clear skies with low to moderate aerosol loading. Totally overcast data were obtained during the morning of one day. Five of the measurements are reproducible to about 2 W/m 2 at the 95% confidence level. Three more agree with the mean of these five to about 4 W/m 2 at the 95% confidence level after correction for thermal offsets. Citation: Michalsky, J. J., et al., Results from the first ARM diffuse horizontal shortwave irradiance comparison,
Journal of Geophysical Research: Atmospheres, 2001
Because atmospheric longwave radiation is one of the most fundamental elements of an expected climate change, there has been a strong interest in improving measurements and model calculations in recent years. Important questions are how reliable and consistent are atmospheric longwave radiation measurements and calculations and what are the uncertainties? The First International Pyrgeometer and Absolute Skyscanning Radiometer Comparison, which was held at the Atmospheric Radiation Measurement program's Southern Great Plains site in Oklahoma, answers these questions at least for midlatitude summer conditions and reflects the state of the art for atmospheric longwave radiation measurements and calculations. The 15 participating pyrgeometers were all calibration-traced standard instruments chosen from a broad international community. Two new chopped pyrgeometers also took part in the comparison. An absolute sky-scanning radiometer (ASR), which includes a pyroelectric detector and a reference blackbody source, was used for the first time as a reference standard instrument to field calibrate pyrgeometers during clear-sky nighttime measurements. Owner-provided and uniformly determined blackbody calibration factors were compared. Remarkable improvements and higher pyrgeometer precision were achieved with field calibration factors. Results of nighttime and daytime pyrgeometer precision and absolute uncertainty are presented for eight consecutive days of measurements, during which period downward longwave irradiance varied between 260 and 420 W m Ϫ2 . Comparisons between pyrgeometers and the absolute ASR, the atmospheric emitted radiance interferometer, and radiative transfer models LBLRTM and MODTRAN show a surprisingly good agreement of Ͻ2 W m Ϫ2 for nighttime atmospheric longwave irradiance measurements and calculations.
2020
Industry advances have greatly reduced the cost and size of ground-based shortwave (SW) sensors for the ultraviolet, visible, and near-infrared spectral ranges that make up the solar spectrum, while simultaneously increasing their ruggedness, reliability, and calibration accuracy needed for outdoor operation. These sensors and collocated meteorological equipment are an important part of the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) User Facility, which has supported parallel integrated measurements of atmospheric and surface properties for more than two decades at fixed and mobile sites around the world. The versatile capability of these ground-based measurements includes 1) rich spectral information required for retrieving cloud and aerosol microphysical properties, such as cloud phase, cloud particle size, and aerosol size distributions, and 2) high temporal resolution needed for capturing fast evolution of cloud microphysical properties in response t...
Journal of Geophysical Research, 2000
Motivated by recent studies suggesting that the clear-sky atmosphere absorbs more shortwave (solar) radiation than the theoretical models, we have performed two consistency tests on the data used in several of these studies. These data consist of broadband measurements of shortwave irradiance to the surface (total, direct, and diffuse) taken in Oklahoma. In the absence of aerosols, Rayleigh scattering is the sole source of diffuse radiation and thus without any unknown source of atmospheric SW absorption, the measured diffuse irradiance should not be less than that produced by a model incorporating both Rayleigh scattering and conventional atmospheric absorption. The measurements of broadband diffuse irradiance, however, exhibit considerable sub-Rayleigh behavior. On the other hand, measurements of the diffuse irradiance in narrow spectral bands, centered at 415, 500, and 608 nm, indicate no sub-Rayleigh behavior, suggesting that exhibited by the broadband measurements is probably unrealistic. Related to this is the finding that the total surface SW irradiance, when evaluated as the sum of the directbeam irradiance (pyrheliometer) and the diffuse irradiance (shaded pyranometer), differs considerably and diurnally from the single measurement of the total irradiance by the unshaded pyranometer under conditions in which possible cosine response errors of the unshaded pyranometer have been minimized. This indicates that the pyranometer daytime offsets differ from each other, suggesting their daytime offsets likewise differ from their nighttime offsets, which are nearly identical. We emphasize that these conclusions apply solely to the data for Oklahoma, and they are focused upon obtaining a better understanding of the clear-sky absorption problem that analyses of these data have raised. 24,881 24,882 CESS ET AL.' ATMOSPHERIC RADIATION MEASUREMENTS RADIATION MEASUREMENTS 24,885