Close packing effects on clean and dirty snow albedo and associated climatic implications

He, Cenlin; Takano, Y.; Liou, Kuo‐Nan

doi:10.1002/2017gl072916

Cited by 31 publications

(24 citation statements)

References 58 publications

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“…These values are, in fact, closer to the g of large spherical snow grains (g ≈ 0.89) or that of spheroids with an aspect ratio of 0.5 (g ≈ 0.86; Fig. 4 in He et al, 2017b) than that of the OHC. Therefore, should the values derived by Ottaviani et al (2015) be typical of snow, the use of the OHC would tend to overestimate snow albedo.…”

Section: Uncertainties In Snow Albedo Calculationsupporting

confidence: 59%

“…This choice was based on fitting the phase function to measurements of angular scattering by blowing snow. Very recently, He et al (2017b) developed another parameterization for the co-albedo and asymmetry parameter of snow for potential use in snow, land surface, and climate models, based on single-scattering calculations for spheres and three non-spherical shapes. This parameterization can be used for clean as well as dirty snow, as it includes the effects on co-albedo due to black carbon internally mixed with snow.…”

Section: Introductionmentioning

confidence: 99%

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Response to Cenlin He

Räisänen¹

2017

Preprint

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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 small. Finally, the impact of assumed snow grain shape on the radiative effects of absorbing aerosols in snow is discussed.

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Section: Uncertainties In Snow Albedo Calculationsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Response to Cenlin He

Räisänen¹

2017

Preprint

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“…Light attenuation within the snowpack is related to the density of the scattering elements per unit volume. In addition, layer structure, grain shape, anthropogenic and natural impurities (such as black carbon, dust and algae) and close-packing effects of snow grains affect scattering properties and thus, the albedo of a snowpack (Warren and Wiscombe, 1980;Kokhanovsky and Zege, 2004;Aoki et al, 2011;Kokhanovsky, 2013;Libois et al, 2013;Libois et al, 2014;Komuro and Suzuki, 2015;Peltoniemi et al, 2015;Pirazzini et al, 2015;Räisänen et al, 2015;Cook et al, 2017;He et al, 2017, Kokhanovsky et al, 2018. Several models for the coupled mass and energy balances of snow on the ground have also been developed (Flanner and Zender, 2006;Essery, 2015).…”

Section: Introductionmentioning

confidence: 99%

Effect of small-scale snow surface roughness on snow albedo and reflectance

Manninen¹,

Anttila²,

Jääskeläinen³

et al. 2020

Preprint

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Abstract. The primary goal of this paper is to present a model of snow surface albedo accounting for small-scale surface roughness effects. The model is based on photon recollision probability and it can be combined with existing bulk volume albedo models, such as TARTES. The model is fed with in situ measurements of surface roughness from plate profile and laser scanner data, and it is evaluated by comparing the computed albedos with observations. It provides closer results to empirical values than volume scattering based albedo simulations alone. The impact of surface roughness on albedo increases with the progress of the melting season and is larger for larger solar zenith angles. In absolute terms, surface roughness can decrease the total albedo by up to about 0.1. As regards the bidirectional reflectance factor (BRF), it is found that surface roughness increases backward scattering especially for large solar zenith angle values.

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“…Based on previous studies (Hansen and Nazarenko, 2004;Hansen et al, 2005), IPCC (2007) showed the radiative forcing range of 0.10 ± 0.10 W m −2 induced by aerosol in snow at the global scale, whereas IPCC (2013) adopted a radiative forcing of +0.04 (+0.02 to +0.09) W m −2 according to the results of Bond et al (2013). Recent studies have shown the significant impacts of snow grain shape (spherical vs. nonspherical) and aerosol-snow mixing state (internal vs. external) on BC and dust-in-snow radiative forcing (e.g., Flanner et al, 2012;Liou et al, 2014;Dang et al, 2016;He et al, 2017bHe et al, , 2018a. Further studies also show the effects of snow grain packing (He et al, 2017a) and aerosol size distribution in snow (Schwarz et al, 2013;He et al, 2018b) on aerosol-snow interactions.…”

Section: Introductionmentioning

confidence: 99%

Radiative feedbacks of dust in snow over eastern Asia in CAM4-BAM

et al. 2018

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Abstract. Dust in snow on the Tibetan Plateau (TP) could reduce the visible snow albedo by changing surface optical properties and removing the snow cover through increased snowmelt, which leads to a significant positive radiative forcing and remarkably alters the regional energy balance and the eastern Asian climate system. This study extends our previous investigation in dust–radiation interactions to investigate the dust-in-snow radiative forcing (SRF) and its feedbacks on the regional climate and the dust cycle over eastern Asia through the use of the Community Atmosphere Model version 4 with a Bulk Aerosol Model parameterizations of the dust size distribution (CAM4-BAM). Our results show that SRF increases the eastern Asian dust emissions significantly by 13.7 % in the spring, countering a 7.6 % decrease in the regional emissions by the dust direct radiative forcing (DRF). SRF also remarkably affects the whole dust cycle, including transport and deposition of dust aerosols over eastern Asia. The simulations indicate an increase in dust emissions of 5.1 %, due to the combined effect of DRF and SRF. Further analysis reveals that these results are mainly due to the regional climatic feedbacks induced by SRF over eastern Asia. By reducing the snow albedo over the TP, the dust in snow mainly warms the TP and influences its thermal effects by increasing the surface sensible and latent heat flux, which in turn increases the aridity and westerly winds over northwestern China and affects the regional dust cycle. Additionally, the dust in snow also accelerates the snow-melting process, reduces the snow cover and then expands the eastern Asian dust source region, which results in increasing the regional dust emissions. Hence, a significant feature of SRF on the TP is the creation of a positive feedback loop that affects the dust cycle over eastern Asia.

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Close packing effects on clean and dirty snow albedo and associated climatic implications

Cited by 31 publications

References 58 publications

Response to Cenlin He

Response to Cenlin He

Effect of small-scale snow surface roughness on snow albedo and reflectance

Radiative feedbacks of dust in snow over eastern Asia in CAM4-BAM

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