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Attenuation coefficient of usable solar radiation of the global oceans
Author(s) -
Lin Junfang,
Lee Zhongping,
Ondrusek Michael,
Kahru Mati
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2015jc011528
Subject(s) - downwelling , water column , attenuation , attenuation coefficient , range (aeronautics) , ocean gyre , radiation , environmental science , atmospheric sciences , computational physics , oceanography , materials science , physics , optics , geology , subtropics , upwelling , fishery , composite material , biology
Usable solar radiation (USR) represents spectrally integrated solar energy in the spectral range of 400–560 nm, a domain where photons penetrate the most in oceanic waters and thus contribute to photosynthesis and heating at deeper depths. Through purely numerical simulations, it was found that the diffuse attenuation coefficient of downwelling USR ( K d (USR), m −1 ) is nearly a constant vertically in the upper water column for clear waters and most turbid waters. Subsequently an empirical model was developed to estimate K d (USR) based on the diffuse attenuation coefficient at 490 nm ( K d (490), m −1 ). We here evaluate this relationship using data collected from a wide range of oceanic and coastal environments and found that the relationship between K d (490) and K d (USR) developed via the numerical simulation is quite robust. We further refined this relationship to extend the applicability to “clearest” natural waters. This refined relationship was then used to produce sample distribution of K d (USR) of global oceans. As expected, extremely low K d (USR) (∼0.02 m −1 ) was observed in ocean gyres, while significantly higher K d (USR) (∼5.2 m −1 ) was found in very turbid coastal regions. A useful application of K d (USR) is to easily and accurately propagate surface USR to deeper depths, potentially to significantly improve the estimation of basin scale primary production and heat fluxes in the upper water column.