The Solar Ultraviolet Environment at the Ocean.

Area of Science:

• Atmospheric Science
• Ocean Optics
• Radiative Transfer

Background:

• Understanding ultraviolet (UV) radiation exposure over aquatic environments is crucial for assessing biological impacts.
• Spectral radiance calculations are essential for modeling UV penetration and biological dose in water.

Purpose of the Study:

• To compute spectral radiances and estimate erythemal exposures over water under various atmospheric and oceanic conditions.
• To quantify the contributions of direct sun, diffuse sky, sea surface reflection, and water-leaving radiance to total UV exposure.

Main Methods:

• Utilized atmospheric and oceanic radiative transfer models to compute spectral radiances (285-400 nm).
• Simulated clear, hazy, and cloudy sky conditions with varying solar zenith angles, wind speeds, and ozone concentrations.
• Tracked contributions from direct beam, diffuse-sky, sea surface reflected, and water-leaving radiance.

Main Results:

• Diffuse-sky irradiance often exceeds direct-sun irradiance below 330 nm.
• Reflected and water-leaving irradiance contribute less than 20% to vertical surface UV exposure.
• Total UV exposure is highly dependent on solar and azimuth angles; sea surface roughness has minimal impact.

Conclusions:

• UV exposure over water is significantly influenced by atmospheric conditions and solar geometry.
• In clear waters with high sun angles, substantial UV index values can penetrate to depths of several meters.
• Models provide critical data for understanding UV radiation dynamics in aquatic ecosystems.