09 September 2019

New Shortwave Radiative Transfer Module SNICAR-AD Improves E3SM-Simulated Snow Radiative Properties

SNICAR-AD can be turned on in MPAS-seaice and ELM for consistent simulation of snow albedo and solar absorption.

Science

Snow has the highest albedo of all natural surfaces on Earth; an accurate simulation of the shortwave radiative properties of snowpack is therefore crucial for spectrally partitioning solar energy and representing snow-albedo feedbacks across the Earth system. E3SM inherited two different radiative transfer modules for snow on sea ice and snow on land, respectively, that predict different snow solar radiative properties. Researchers at UC Irvine inter-compared, evaluated, and improved these modules, then formulated and implemented a hybrid scheme SNICAR-AD that can be utilized by both sea ice and land components of E3SM for consistent and improved simulation of snow albedo and solar absorption.

Impact

Researchers formulated a hybrid radiative transfer module SNICAR-AD that more accurately computes snow radiative properties on any cryospheric surface. SNICAR-AD removes the previous discrepancies in snow radiative properties between different model components, corrects for their common biases at low sun-angles, and improves the accuracy of snowpack heating by sunlight. These developments are especially significant for investigating the middle and high latitude processes, such as snow albedo feedback, aerosol-in-snow radiative effects, and sea-ice and snow cover extent and seasonality.

Summary

Snow cover on land, land ice, and sea ice modulates the surface energy balance of middle and high latitudes of the Earth, principally because even a thin layer of snow can greatly increase the surface albedo. E3SM v1 adopts two different shortwave radiative transfer modules to compute the snow albedo and solar absorption; the same snow, therefore, has different solar radiative properties depending whether it is on land or on sea ice. These differences are model artifacts that should be eliminated so that snow has consistent properties across the Earth system.

In this study, scientists inter-compared and evaluated these modules against an offline benchmark model to formulate an improved and universal scheme SNICAR-AD that can be used to compute snow shortwave radiative properties everywhere in the Earth system. Improved treatment of surface cryospheric radiative properties in the thermal infrared has recently been shown to remediate significant climate simulation biases in Polar Regions. It is hoped that the adoption of improved and consistent treatments of solar radiative properties for snow-covered surfaces as described in this study will further remediate simulation biases in snow-covered regions. SNICAR-AD is now implemented in the sea-ice and land components of E3SM v2.

Contact
Cheng Dang
University of California - Irvine