Ocean radiant heating. Part I: Optical influences

Radiative transfer calculations are used to quantify the effects of physica l and biological processes on variations in the transmission of solar radia tion through the upper ocean. Results indicate that net irradiance at 10 cm and 5 m can vary by 23 and 34 W m(-2), respectively, due to changes in the chlorophyll concentration, cloud amount, and solar zenith angle (when norm alized to a climatological surface irradiance of 200 W m(-2)). Chlorophyll influences solar attenuation in the visible wavebands, and thus has little effect on transmission within the uppermost meter where the quantity of nea r-infrared energy is substantial. Beneath the top few meters, a chlorophyll increase from 0.03 to 0.3 mg m(-3) can result in a solar Bur decrease of m ore than 10 W m(-2). Clouds alter the spectral composition of the incident irradiance by preferentially attenuating in the near-infrared region, and s erve to increase solar transmission in the upper few meters as a greater po rtion of the irradiance exists in the deep-penetrating, visible wavebands. A 50% reduction in the incident irradiance by clouds causes a near 60% redu ction in the radiant heating rate for the top 10 cm of the ocean. Solar zen ith angle influences transmission during clear sky periods through changes in sea-surface albedo. This study provides necessary information for improv ed physically and biologically based solar transmission parameterizations t hat will enhance upper ocean modeling efforts and sea-surface temperature p rediction.