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...
Published in: | The Cryosphere |
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Format: | Article in Journal/Newspaper |
Language: | English |
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COPERNICUS GESELLSCHAFT MBH
2018
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Online Access: | http://hdl.handle.net/10138/230190 |
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ftunivhelsihelda:oai:helda.helsinki.fi:10138/230190 |
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openpolar |
institution |
Open Polar |
collection |
HELDA – University of Helsinki Open Repository |
op_collection_id |
ftunivhelsihelda |
language |
English |
topic |
SEA-ICE BIDIRECTIONAL REFLECTANCE MULTIPLE-SCATTERING SPECTRAL ALBEDO ANTARCTIC SNOW SURFACE-AREA BLACK CARBON ARCTIC SNOW SOLAR LIGHT DATA RECORD 114 Physical sciences |
spellingShingle |
SEA-ICE BIDIRECTIONAL REFLECTANCE MULTIPLE-SCATTERING SPECTRAL ALBEDO ANTARCTIC SNOW SURFACE-AREA BLACK CARBON ARCTIC SNOW SOLAR LIGHT DATA RECORD 114 Physical sciences Räisänen, Petri Makkonen, Risto Kirkevag, Alf Debernard, Jens B. Effects of snow grain shape on climate simulations : sensitivity tests with the Norwegian Earth System Model |
topic_facet |
SEA-ICE BIDIRECTIONAL REFLECTANCE MULTIPLE-SCATTERING SPECTRAL ALBEDO ANTARCTIC SNOW SURFACE-AREA BLACK CARBON ARCTIC SNOW SOLAR LIGHT DATA RECORD 114 Physical sciences |
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 (similar to 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. -0.22Wm(-2). Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2m air temperature in NONSPH is 1.17K 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 ... |
author2 |
Department of Physics |
format |
Article in Journal/Newspaper |
author |
Räisänen, Petri Makkonen, Risto Kirkevag, Alf Debernard, Jens B. |
author_facet |
Räisänen, Petri Makkonen, Risto Kirkevag, Alf Debernard, Jens B. |
author_sort |
Räisänen, Petri |
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 GESELLSCHAFT MBH |
publishDate |
2018 |
url |
http://hdl.handle.net/10138/230190 |
geographic |
Antarctic Arctic |
geographic_facet |
Antarctic Arctic |
genre |
albedo Antarc* Antarctic Arctic black carbon Sea ice |
genre_facet |
albedo Antarc* Antarctic Arctic black carbon Sea ice |
op_relation |
10.5194/tc-11-2919-2017 Petri Raisanen acknowledges funding by the Academy of Finland through the NABCEA project (decision number 296302). Alf Kirkevag and Jens B. Debernard have been funded by the Research Council of Norway through the EarthClim (20771/E10), EVA(229771), NOTUR(nn2345k) and Norstore (ns2345k) projects, by the Nordic Centers of Excellence CRAICC and eSTICC, and by the EU FP7 projects PEGASOS and ACCESS. Mark Flanner is thanked for providing the spectral distribution of downwelling solar radiation for midlatitude winter conditions. We also wish to thank the data providers: ECMWF for the ERA-Interim data, NOAA for the snow cover and sea ice climate data records, NASA Langley Research Center Atmospheric Science Data Center for the MODIS and CERES EBAF data, and EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) for the CLARA-A2 data. Finally, the anonymous reviewers are thanked for their constructive comments on the original manuscript. Räisänen , P , Makkonen , R , Kirkevag , A & Debernard , J B 2017 , ' Effects of snow grain shape on climate simulations : sensitivity tests with the Norwegian Earth System Model ' , Cryosphere , vol. 11 , no. 6 , pp. 2919-2942 . https://doi.org/10.5194/tc-11-2919-2017 85038441558 467c1935-a19d-4276-9905-6b4d273ca3d8 http://hdl.handle.net/10138/230190 000417904200001 |
op_rights |
cc_by openAccess info:eu-repo/semantics/openAccess |
container_title |
The Cryosphere |
container_volume |
11 |
container_issue |
6 |
container_start_page |
2919 |
op_container_end_page |
2942 |
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1787429487948857344 |
spelling |
ftunivhelsihelda:oai:helda.helsinki.fi:10138/230190 2024-01-07T09:38:04+01:00 Effects of snow grain shape on climate simulations : sensitivity tests with the Norwegian Earth System Model Räisänen, Petri Makkonen, Risto Kirkevag, Alf Debernard, Jens B. Department of Physics 2018-01-04T08:44:00Z 24 application/pdf http://hdl.handle.net/10138/230190 eng eng COPERNICUS GESELLSCHAFT MBH 10.5194/tc-11-2919-2017 Petri Raisanen acknowledges funding by the Academy of Finland through the NABCEA project (decision number 296302). Alf Kirkevag and Jens B. Debernard have been funded by the Research Council of Norway through the EarthClim (20771/E10), EVA(229771), NOTUR(nn2345k) and Norstore (ns2345k) projects, by the Nordic Centers of Excellence CRAICC and eSTICC, and by the EU FP7 projects PEGASOS and ACCESS. Mark Flanner is thanked for providing the spectral distribution of downwelling solar radiation for midlatitude winter conditions. We also wish to thank the data providers: ECMWF for the ERA-Interim data, NOAA for the snow cover and sea ice climate data records, NASA Langley Research Center Atmospheric Science Data Center for the MODIS and CERES EBAF data, and EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) for the CLARA-A2 data. Finally, the anonymous reviewers are thanked for their constructive comments on the original manuscript. Räisänen , P , Makkonen , R , Kirkevag , A & Debernard , J B 2017 , ' Effects of snow grain shape on climate simulations : sensitivity tests with the Norwegian Earth System Model ' , Cryosphere , vol. 11 , no. 6 , pp. 2919-2942 . https://doi.org/10.5194/tc-11-2919-2017 85038441558 467c1935-a19d-4276-9905-6b4d273ca3d8 http://hdl.handle.net/10138/230190 000417904200001 cc_by openAccess info:eu-repo/semantics/openAccess SEA-ICE BIDIRECTIONAL REFLECTANCE MULTIPLE-SCATTERING SPECTRAL ALBEDO ANTARCTIC SNOW SURFACE-AREA BLACK CARBON ARCTIC SNOW SOLAR LIGHT DATA RECORD 114 Physical sciences Article publishedVersion 2018 ftunivhelsihelda 2023-12-14T00:01:14Z 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 (similar to 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. -0.22Wm(-2). Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2m air temperature in NONSPH is 1.17K 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 ... Article in Journal/Newspaper albedo Antarc* Antarctic Arctic black carbon Sea ice HELDA – University of Helsinki Open Repository Antarctic Arctic The Cryosphere 11 6 2919 2942 |