Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model
Snow consists of non-spherical grains of various shapes and sizes. Still, in radiative transfer calculations, snow grains are often treated as spherical. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, ve...
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fttriple:oai:gotriple.eu:oai:doaj.org/article:badd76685610462fb02dd53ef28a99dc 2023-05-15T18:18:17+02:00 Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model P. Räisänen R. Makkonen A. Kirkevåg J. B. Debernard 2017-12-01 https://doi.org/10.5194/tc-11-2919-2017 https://www.the-cryosphere.net/11/2919/2017/tc-11-2919-2017.pdf https://doaj.org/article/badd76685610462fb02dd53ef28a99dc en eng Copernicus Publications doi:10.5194/tc-11-2919-2017 1994-0416 1994-0424 https://www.the-cryosphere.net/11/2919/2017/tc-11-2919-2017.pdf https://doaj.org/article/badd76685610462fb02dd53ef28a99dc undefined The Cryosphere, Vol 11, Pp 2919-2942 (2017) geo envir Journal Article https://vocabularies.coar-repositories.org/resource_types/c_6501/ 2017 fttriple https://doi.org/10.5194/tc-11-2919-2017 2023-01-22T17:50:04Z Snow consists of non-spherical grains of various shapes and sizes. Still, in radiative transfer calculations, snow grains are often treated as spherical. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, version 4 (CICE4), both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM). In this study, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH) is compared with another (NONSPH) in which the snow shortwave single-scattering properties are based on a combination of three non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (0.77–0.78 in the visible region) than in the spherical case ( ≈ 0.89). Therefore, for the same effective snow grain size (or equivalently, the same specific projected area), the snow broadband albedo is higher when assuming non-spherical rather than spherical snow grains, typically by 0.02–0.03. Considering the spherical case as the baseline, this results in an instantaneous negative change in net shortwave radiation with a global-mean top-of-the-model value of ca. −0.22 W m−2. Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2 m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further demonstrated that the effect of snow grain shape could be largely offset by adjusting the snow grain size. When assuming non-spherical snow grains with the parameterized grain size increased by ca. 70 %, the climatic differences to the SPH experiment become very ... Article in Journal/Newspaper Sea ice The Cryosphere Unknown The Cryosphere 11 6 2919 2942 |
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geo envir P. Räisänen R. Makkonen A. Kirkevåg J. B. Debernard Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
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geo envir |
description |
Snow consists of non-spherical grains of various shapes and sizes. Still, in radiative transfer calculations, snow grains are often treated as spherical. This also applies to the computation of snow albedo in the Snow, Ice, and Aerosol Radiation (SNICAR) model and in the Los Alamos sea ice model, version 4 (CICE4), both of which are employed in the Community Earth System Model and in the Norwegian Earth System Model (NorESM). In this study, we evaluate the effect of snow grain shape on climate simulated by NorESM in a slab ocean configuration of the model. An experiment with spherical snow grains (SPH) is compared with another (NONSPH) in which the snow shortwave single-scattering properties are based on a combination of three non-spherical snow grain shapes optimized using measurements of angular scattering by blowing snow. The key difference between these treatments is that the asymmetry parameter is smaller in the non-spherical case (0.77–0.78 in the visible region) than in the spherical case ( ≈ 0.89). Therefore, for the same effective snow grain size (or equivalently, the same specific projected area), the snow broadband albedo is higher when assuming non-spherical rather than spherical snow grains, typically by 0.02–0.03. Considering the spherical case as the baseline, this results in an instantaneous negative change in net shortwave radiation with a global-mean top-of-the-model value of ca. −0.22 W m−2. Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2 m air temperature in NONSPH is 1.17 K lower than in SPH, with substantially larger differences at high latitudes. The climatic response is amplified by strong snow and sea ice feedbacks. It is further demonstrated that the effect of snow grain shape could be largely offset by adjusting the snow grain size. When assuming non-spherical snow grains with the parameterized grain size increased by ca. 70 %, the climatic differences to the SPH experiment become very ... |
format |
Article in Journal/Newspaper |
author |
P. Räisänen R. Makkonen A. Kirkevåg J. B. Debernard |
author_facet |
P. Räisänen R. Makkonen A. Kirkevåg J. B. Debernard |
author_sort |
P. Räisänen |
title |
Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
title_short |
Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
title_full |
Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
title_fullStr |
Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
title_full_unstemmed |
Effects of snow grain shape on climate simulations: sensitivity tests with the Norwegian Earth System Model |
title_sort |
effects of snow grain shape on climate simulations: sensitivity tests with the norwegian earth system model |
publisher |
Copernicus Publications |
publishDate |
2017 |
url |
https://doi.org/10.5194/tc-11-2919-2017 https://www.the-cryosphere.net/11/2919/2017/tc-11-2919-2017.pdf https://doaj.org/article/badd76685610462fb02dd53ef28a99dc |
genre |
Sea ice The Cryosphere |
genre_facet |
Sea ice The Cryosphere |
op_source |
The Cryosphere, Vol 11, Pp 2919-2942 (2017) |
op_relation |
doi:10.5194/tc-11-2919-2017 1994-0416 1994-0424 https://www.the-cryosphere.net/11/2919/2017/tc-11-2919-2017.pdf https://doaj.org/article/badd76685610462fb02dd53ef28a99dc |
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undefined |
op_doi |
https://doi.org/10.5194/tc-11-2919-2017 |
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The Cryosphere |
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11 |
container_issue |
6 |
container_start_page |
2919 |
op_container_end_page |
2942 |
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