Abstract
The Atacama Desert has been pointed out as one of the places on earth where the highest surface irradiance may occur. This area is characterized by its high altitude, prevalent cloudless conditions and relatively low columns of ozone and water vapor. Aimed at the characterization of the solar spectrum in the Atacama Desert, we carried out in February-March 2015 ground-based measurements of the spectral irradiance (from the ultraviolet to the near infrared) at seven locations that ranged from the city of Antofagasta (on the southern pacific coastline) to the Chajnantor Plateau (5,100 m altitude). Our spectral measurements allowed us to retrieve the total ozone column, the precipitable water, and the aerosol properties at each location. We found that changes in these parameters, as well as the shorter optical path length at high-altitude locations, lead to significant increases in the surface irradiance with the altitude. Our measurements show that, in the range 0–5100 m altitude, surface irradiance increases with the altitude by about 27% in the infrared range, 6% in the visible range, and 20% in the ultraviolet range. Spectral measurements carried out at the Izaña Observatory (Tenerife, Spain), in Hannover (Germany) and in Santiago (Chile), were used for further comparisons.
Highlights
Aimed at the characterization of the spectral irradiance, we carried out ground-based measurements at seven locations in the Atacama Desert that ranged from the city of Antofagasta to the Chajnantor Plateau (5,100 m altitude)
Compared with locations in the northern hemisphere, the Atacama Desert is an area characterized by relatively low TOC values
We confirmed that the ozone column in the Atacama Desert can be in February 50–60 DU lower than the TOC value in June at similar latitudes in the northern hemisphere
Summary
Most instruments that can carry out spectral measurements are fast single-grating spectroradiometers fitted with CCD arrays ( known as polychromators)[22,27,28]. Array instruments are capable of measuring the spectrum in a very short time interval, their measurements at short wavelengths ( in the UV-B) are strongly affected by stray light[29,30,31,32,33]. Intercomparisons involving several CCD arrays have shown significant differences in the measurements at wavelengths shorter than 350 nm[28]. Several ex-post stray light corrections have allowed improving the performance of array spectroradiometers in the UV range[31]. Double monochromator-based spectroradiometers are still recommended for quality-controlled measurements of the surface irradiance ( in the UV part of the spectrum)
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