3.9. Ocean albedo

As summarized in Core concepts, the ocean albedo computation produces four albedos, which are merged with the land and sea-ice albedos and sent to the atmosphere. This page describes how they are computed, in med_phases_ocnalb_mod.F90.

3.9.1. What is computed

Four ocean albedos are produced, spanning the two shortwave bands and the two illumination types:

• So_avsdr — visible, direct

• So_avsdf — visible, diffuse

• So_anidr — near-infrared, direct

• So_anidf — near-infrared, diffuse

The albedos are computed on the ocean grid and held in the internal-state field bundle FBMed_ocnalb_o; they are then mapped to the atmosphere grid (FBMed_ocnalb_a) for the prep_atm merge.

3.9.2. The run phase

The albedo computations depend on the solar zenith angle, so they are recomputed every coupling step for the current zenith angle. The zenith angle is derived from the Earth’s orbital parameters — eccentricity, obliquity and related quantities — which are initialized by med_phases_ocnalb_orbital_init and advanced over the run by med_phases_ocnalb_orbital_update. The run sequence drives the whole computation through med_phases_ocnalb_run.

3.9.3. Options

The albedo calculation is controlled by a few attributes and settings:

• ocean_albedo_scheme — the ocean albedo scheme:

  • 0 — Briegleb et al. (1986)

  • 1 — Taylor et al. (1996)

• flux_albav — if true, use averaged (zenith-angle-independent) diffuse and direct albedos instead of the zenith-angle-dependent calculation.

• use_min_albedo / min_albedo — apply a minimum floor to the direct visible and near-infrared albedos.

• albdir / albdif — the 60-degree reference albedos (direct and diffuse) used by the scheme.

Once computed and mapped to the atmosphere grid, the ocean albedos are merged with the land and sea-ice albedos in prep_atm and sent to the atmosphere for its shortwave radiation calculation (Core concepts).