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Usable solar radiation and its attenuation in the upper water column
Author(s) -
Lee Zhongping,
Shang Shaoling,
Du Keping,
Wei Jianwei,
Ar Robert
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2013jc009507
Subject(s) - attenuation coefficient , attenuation , irradiance , radiation , photosynthetically active radiation , absorption (acoustics) , water column , ocean color , downwelling , environmental science , satellite , materials science , optics , atmospheric sciences , physics , photosynthesis , chemistry , oceanography , geology , upwelling , astronomy , biochemistry
Abstract A new radiometric term named as usable solar radiation (USR) is defined to represent the spectrally integrated solar irradiance in the spectral window of 400–560 nm. Through numerical simulations of optically deep waters covering a wide range of optical properties, it is found that the diffuse attenuation coefficient of downwelling USR, K d (USR), is nearly a constant vertically for almost all oceanic waters (chlorophyll concentration under ∼3 mg m −3 ). This feature is quite contrary to the diffuse attenuation coefficient of the photosynthetic available radiation, K (PAR), which varies significantly from surface to deeper depths for oceanic waters. It is also found that the ratio of the photosynthetic utilizable radiation (PUR) to the product of USR and phytoplankton absorption coefficient at 440 nm approximates a constant for most oceanic waters. These results support the use of a single K d (USR) for each water and each sun angle for accurate estimation of USR propagation, and suggest an efficient approach to estimate PUR( z ) in the upper water column. These results further indicate that it is necessary and valuable for the generation of USR and K d (USR) products from satellite ocean color measurements, which can be used to facilitate the studies of heat transfer and photosynthesis in the global oceans.