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- Author or Editor: Bruce W. Forgan x
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Abstract
A simple method for calibrating reference pyranometers is described. Called the alternate method, it requires monitoring of direct irradiance and diffuse and global irradiance voltages without the need for a calibrated diffuse pyranometer. The method involves alternately using each of the pyranometers for monitoring diffuse and global irradiance voltages and then solving pairs of simultaneous equations for each available zenith angle, where the only unknowns are the directional responses of the pyranometers being calibrated. Results from models and field calibrations show that the uncertainties of the alternate method are less than 1% for solar zenith angles less than 75° and are equal to or better than those determined from the composite method under identical conditions. The new method calibrations am also in good agreement with sun-disk method calibrations. It is argued that by using the alternate method for on-site field calibrations the uncertainties in network measurements can be reduced.
Abstract
A simple method for calibrating reference pyranometers is described. Called the alternate method, it requires monitoring of direct irradiance and diffuse and global irradiance voltages without the need for a calibrated diffuse pyranometer. The method involves alternately using each of the pyranometers for monitoring diffuse and global irradiance voltages and then solving pairs of simultaneous equations for each available zenith angle, where the only unknowns are the directional responses of the pyranometers being calibrated. Results from models and field calibrations show that the uncertainties of the alternate method are less than 1% for solar zenith angles less than 75° and are equal to or better than those determined from the composite method under identical conditions. The new method calibrations am also in good agreement with sun-disk method calibrations. It is argued that by using the alternate method for on-site field calibrations the uncertainties in network measurements can be reduced.
Abstract
Results are presented for perpetual January and July general circulation simulations using the Australian Bureau of Meteorology Research Centre global spectral model. Particular emphasis is placed on the impact of changes in the physical parameterizations and horizontal resolution on the modeled fields. The results include variances and eddy transports as well as zonal means and geographical distributions. Of the experiments conducted the most satisfactory results were obtained using stability-dependent vertical diffusion and a combination of the Kuo scheme for deep convection and the Tiedtke shallow convection scheme.
The simulation of the polar night region of the stratosphere in January was much more realistic than in results obtained using an earlier version of the model. The improvement is attributed to the revised radiation code, supporting the conclusions of Ramanathan et al. on the sensitivity of simulations of this region of the atmosphere to the treatment of radiative processes.
Abstract
Results are presented for perpetual January and July general circulation simulations using the Australian Bureau of Meteorology Research Centre global spectral model. Particular emphasis is placed on the impact of changes in the physical parameterizations and horizontal resolution on the modeled fields. The results include variances and eddy transports as well as zonal means and geographical distributions. Of the experiments conducted the most satisfactory results were obtained using stability-dependent vertical diffusion and a combination of the Kuo scheme for deep convection and the Tiedtke shallow convection scheme.
The simulation of the polar night region of the stratosphere in January was much more realistic than in results obtained using an earlier version of the model. The improvement is attributed to the revised radiation code, supporting the conclusions of Ramanathan et al. on the sensitivity of simulations of this region of the atmosphere to the treatment of radiative processes.
Abstract
Diffuse-sky solar irradiance is an important quantity for radiation budget research, particularly as it relates to climate. Diffuse irradiance is one component of the total downwelling solar irradiance and contains information on the amount of downward-scattered, as opposed to directly transmitted, solar radiation. Additionally, the diffuse component is often required when calibrating total irradiance radiometers. A variety of pyranometers are commonly used to measure solar diffuse irradiance. An examination of some instruments for measuring diffuse irradiance using solar tracking shade disks is presented, along with an evaluation of the achieved accuracy. A data correction procedure that is intended to account for the offset caused by thermal IR exchange between the detector and filter domes in certain common diffuse pyranometers is developed and validated. The correction factor is derived from outputs of a collocated pyrgeometer that measures atmospheric infrared irradiance.
Abstract
Diffuse-sky solar irradiance is an important quantity for radiation budget research, particularly as it relates to climate. Diffuse irradiance is one component of the total downwelling solar irradiance and contains information on the amount of downward-scattered, as opposed to directly transmitted, solar radiation. Additionally, the diffuse component is often required when calibrating total irradiance radiometers. A variety of pyranometers are commonly used to measure solar diffuse irradiance. An examination of some instruments for measuring diffuse irradiance using solar tracking shade disks is presented, along with an evaluation of the achieved accuracy. A data correction procedure that is intended to account for the offset caused by thermal IR exchange between the detector and filter domes in certain common diffuse pyranometers is developed and validated. The correction factor is derived from outputs of a collocated pyrgeometer that measures atmospheric infrared irradiance.
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.
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.
