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DOI	10.5194/tc-11-2919-2017
	Effects of snow grain shape on climate simulations: Sensitivity tests with the Norwegian Earth System Model
	Räisänen P.; Makkonen R.; Kirkeväg A.; Debernard J.B.
发表日期	2017
ISSN	19940416
卷号	11 期号:6
英文摘要	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 ( ĝ‰ ĝ€†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. ĝ'0.22ĝ€Wĝ€†mĝ'2. Although this global-mean radiative effect is rather modest, the impacts on the climate simulated by NorESM are substantial. The global annual-mean 2ĝ€m air temperature in NONSPH is 1.17ĝ€†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. 70ĝ€%, the climatic differences to the SPH experiment become very small. Finally, the impact of assumed snow grain shape on the radiative effects of absorbing aerosols in snow is discussed. © Author(s) 2017.
学科领域	aerosol; air temperature; albedo; atmospheric modeling; climate effect; climate modeling; radiative transfer; sea ice; sensitivity analysis; shortwave radiation; simulation; snow cover
语种	英语
scopus关键词	aerosol; air temperature; albedo; atmospheric modeling; climate effect; climate modeling; radiative transfer; sea ice; sensitivity analysis; shortwave radiation; simulation; snow cover
来源期刊	Cryosphere
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/119290
作者单位	Finnish Meteorological Institute, P.O. Box 503, Helsinki, 00101, Finland; Dept. of Physics, University of Helsinki, P.O. Box 64, Helsinki, 00014, Finland; Norwegian Meteorological Institute, P.O. Box 43, Blindern, Oslo, 0313, Norway
推荐引用方式 GB/T 7714	Räisänen P.,Makkonen R.,Kirkeväg A.,et al. Effects of snow grain shape on climate simulations: Sensitivity tests with the Norwegian Earth System Model[J],2017,11(6).
APA	Räisänen P.,Makkonen R.,Kirkeväg A.,&Debernard J.B..(2017).Effects of snow grain shape on climate simulations: Sensitivity tests with the Norwegian Earth System Model.Cryosphere,11(6).
MLA	Räisänen P.,et al."Effects of snow grain shape on climate simulations: Sensitivity tests with the Norwegian Earth System Model".Cryosphere 11.6(2017).