I5.8 Spectrally Resolved Sea-Ice Emissivity

Abstract

Most simulations of longwave emission from sea ice assume a single greybody emissivity. It is increasingly recognized that sea-ice emissivity varies significantly across the electromagnetic spectrum, including in the infrared (IR) region of terrestrial radiation. Thus far coupled-model studies have focused on spectrally varying emissivity effects within the atmospheric model since it already uses multi-band longwave radiative transfer. These studies indicate that the reduced terrestrial emission from open ocean compared to sea ice in the far IR due to emissivity differences is a potential feedback, which has yet to be represented fully in the surface models. This study changes a sea-ice model (CICE) to employ a multi-band longwave physics with spectrally varying emissivity in order to re-examine the surface energy balance of sea ice Physically realistic ice emissivity in the far IR can differ from greybody emissivity by roughly 12%. Using CICE forced by atmospheric reanalyses we isolate the effects of spectrally resolved emissivity on the sea-ice state and surface energy balance. Preliminary results show that this spectrally dependant emissivity decreases the average longwave emission from the sea ice in the Arctic by ~0.2 W m-2 over areas that show no change in ice coverage, with decreases in monthly averages as large as ~0.7 W m-2 in summer. Arctic sea ice annual average area was similarly decreased ~5,580 km2 with a summer monthly decrease of up to ~ 26,000 km2. An experiment with atmospheric coupling would likely lead to larger changes due to feedbacks. This experiment is a first step toward fully coupled ESM experiments with spectrally varying emissivity in all surface model components.