Transmittance index characterization at two solar measurement stations in Brazil

This paper constructs probability density distributions of direct normal, diffuse horizontal, and global horizontal irradiance for 1-min clearness indexes k b , k d , and  k t , respectively. Previous studies on the clearness index, conditioned to the optical air mass, are analyzed and distributions...

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Bibliographic Details
Published in:Theoretical and applied climatology 2020, Vol.139 (1-2), p.205-219
Main Authors: Relva, Stefania Gomes, Gimenes, André Luiz Veiga, Udaeta, Miguel Edgar Morales, Galvão, Luiz Cláudio Ribeiro
Format: Article
Language:English
Subjects:
Air conditioners
Air masses
Analysis
Aquatic Pollution
Atmosphere
Atmospheric conditions
Atmospheric Protection/Air Quality Control/Air Pollution
Atmospheric Sciences
Clearness index
Climate science
Climatology
Cloud formation
Clouds
Density
Density distribution
Dependence
Distribution (Probability theory)
Earth and Environmental Science
Earth Sciences
Irradiance
Measurement
Measuring instruments
Original Paper
Pollution
Pollution levels
Probability theory
Radiation
Radiation measurement
Relative humidity
Rural areas
Specific humidity
Stations
Transmittance
Waste Water Technology
Water Management
Water Pollution Control
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Summary:This paper constructs probability density distributions of direct normal, diffuse horizontal, and global horizontal irradiance for 1-min clearness indexes k b , k d , and  k t , respectively. Previous studies on the clearness index, conditioned to the optical air mass, are analyzed and distributions of these three indexes, using data from two solarimetric stations in Brazil, are presented. The pattern found in probability density distributions, in general, matches the patterns found in the literature. The 50th percentile (P50) of k b values from Sao Paulo city (a location with high levels of pollution) is 0.22, and from the countryside region of the state of Sao Paulo (a location with expected low levels of pollution), it is 0.55. Regarding k t values, P50 is 0.57 and 0.72 for these two regions, respectively. We conclude that different atmospheric conditions result in a different dependence relation between probability density distribution and air mass increases. These conditions include not only cloud formation, but also pollution levels and the influence of relative humidity. These specific results endorse the need for local radiation measurements to the characterization of few-minute average of transmittance indexes.
ISSN:0177-798X
1434-4483
DOI:10.1007/s00704-019-02941-6