Cloud effective transmittance at two sites of the Atacama Desert, Chile

Broadband overcast cloud effective transmittance was determined at Arica (18.47°S, 70.31°W, 20 m above sea level (asl)) and Poconchile (18.45°S, 70.07°W, 560 m asl), Atacama Desert, northern Chile, from 10 min averaged pyranometer measurements of total solar irradiance (ToSI) and ultraviolet solar i...

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Bibliographic Details
Published in:Journal of Geophysical Research 2011-10, Vol.116 (D20), p.1Z-n/a, Article D20205
Main Authors: Luccini, Eduardo, Rivas, Miguel, Rojas, Elisa, Canziani, Pablo
Format: Article
Language:English
Subjects:
Atacama
Atmospheric aerosols
Atmospheric sciences
Chemistry
Climatic conditions
Clouds
Deserts
Geophysics
irradiance
Physics
pyranometer
Radiation
Radiative transfer
solar
Transmittance
Tropical environments
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Summary:Broadband overcast cloud effective transmittance was determined at Arica (18.47°S, 70.31°W, 20 m above sea level (asl)) and Poconchile (18.45°S, 70.07°W, 560 m asl), Atacama Desert, northern Chile, from 10 min averaged pyranometer measurements of total solar irradiance (ToSI) and ultraviolet solar irradiance (UVSI) during the period 2002–2005. The predominant cloud type is marine stratocumulus, characteristic of the southeastern Pacific tropical environment. The region's very regular climate conditions, characterized by overcast mornings and cloudless afternoons, allow the application of an empirical method to determine the expected clear‐sky irradiance during cloudy mornings. The cloud effective transmittance (CET) is determined as the ratio of the measured cloudy‐sky irradiance over the expected clear‐sky irradiance. CETTo = 0.26 (0.31) for ToSI and CETUV = 0.37 (0.43) for UVSI characterize overcast cloudiness at Arica (Poconchile). One‐dimensional radiative transfer model calculations in both ToSI and UVSI ranges are also used. The measured and modeled relationships between CETTo and CETUV closely agree. New insights are given to explain the sparsely populated data around CET = 0.8 observed also by other similar studies. Key Points It determines the cloud effective transmittance at sites of the Atacama Desert It uses an original empirical method to estimate the clear‐sky irradiance It gives new insights to explain observed sparse data around transmittance 0.8
ISSN:0148-0227
2169-897X
2156-2202
2169-8996
DOI:10.1029/2011JD015905