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Abstract
The results of an analysis of simultaneous measurements of incident solar radiation from six locations in metropolitan St. Louis, Missouri are described. The measurements were taken continuously from September 1975 through March 1977 with pyranometers with all-wave and 395 and 695 nm cutoff filters. This report documents typical urban-rural variations of incident solar radiation.
Atmospheric pollutants over the center of metropolitan St. Louis reduced incident all-wave solar irradiation by ∼3%. Under cloudless conditions, differences between urban and rural irradiation were ∼4.5% during winter and 2% in summer. At two suburban sites, the irradiation depletion averaged 1 and 2% for summer and winter seasons, respectively. Under all conditions, the ratios between stations for the complete experiment were similar to those for cloud-free conditions.
Although the comparisons were stratified by wind direction and speed, visibility, time of day and day of the week, only wind direction had a significant effect on the interstation ratios. For cloudless days two suburban sites and a rural site north of the city received ∼3.5% less radiation (compared to a control site) with south than north winds. Wind direction had an effect because pollutants were advected from major sources near the city center. The two urban sites exhibited only ∼1% change due to north-south wind differences. The interstation comparisons for all days were also partitioned by wind direction. With north winds, the suburban and northern rural sites showed ∼2–3% more irradiation (compared to a control site south of the city) on all days than on cloudless days for both the summer period and the complete experiment.
Abstract
The results of an analysis of simultaneous measurements of incident solar radiation from six locations in metropolitan St. Louis, Missouri are described. The measurements were taken continuously from September 1975 through March 1977 with pyranometers with all-wave and 395 and 695 nm cutoff filters. This report documents typical urban-rural variations of incident solar radiation.
Atmospheric pollutants over the center of metropolitan St. Louis reduced incident all-wave solar irradiation by ∼3%. Under cloudless conditions, differences between urban and rural irradiation were ∼4.5% during winter and 2% in summer. At two suburban sites, the irradiation depletion averaged 1 and 2% for summer and winter seasons, respectively. Under all conditions, the ratios between stations for the complete experiment were similar to those for cloud-free conditions.
Although the comparisons were stratified by wind direction and speed, visibility, time of day and day of the week, only wind direction had a significant effect on the interstation ratios. For cloudless days two suburban sites and a rural site north of the city received ∼3.5% less radiation (compared to a control site) with south than north winds. Wind direction had an effect because pollutants were advected from major sources near the city center. The two urban sites exhibited only ∼1% change due to north-south wind differences. The interstation comparisons for all days were also partitioned by wind direction. With north winds, the suburban and northern rural sites showed ∼2–3% more irradiation (compared to a control site south of the city) on all days than on cloudless days for both the summer period and the complete experiment.
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.
