I5.8 Spectrally Resolved Sea-Ice Emissivity

                    

Poster Title

Impacts of spectrally resolved emissivity on the surface energy balance and state of Arctic sea ice

AuthorsZachary Wolff (Unlicensed) and Charlie Zender
First AuthorZachary Wolff (Unlicensed)
Session TypeE3SM/Integrated Session
Session IDI5
Submission TypePoster
GroupCryosphere
ExperimentCryosphere
Poster Link




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.