The Photosynthetically Available Radiation (PAR) data suite provides satellite-based estimates of the downwelling solar radiation in the 400–700 nm range that is available for photosynthesis at the ocean surface. These products quantify the daily or instantaneous amount of usable light energy, expressed in moles of photons m⁻² (commonly noted as “Einstein m⁻²”), and are widely used to estimate marine primary production, interpret phytoplankton bloom dynamics, provide context for optical and biogeochemical measurements,and support ecosystem models and education on light–biology interactions.

Geophysical variables in this suite include:
• par — Daily photosynthetically available radiation (mol photons m⁻² d⁻¹)

The following variables are also included in PACE L2/L3 files:
• l2_flags — Level-2 processing flags (bitmask; see per-variable attributes for flag_masks and flag_meanings)
• ipar — Instantaneous photosynthetically available radiation (mol photons m⁻² s⁻¹)