Stochastic Parameterization for Light Absorption by Internally Mixed BC/dust in Snow Grains for Application to Climate Models

Journal Article · Fri Jun 27 04:00:00 EDT 2014 · Journal of Geophysical Research. D. (Atmospheres), 119(12):7616–7632

DOI:https://doi.org/10.1002/2014JD021665· OSTI ID:1172450

Liou, K. N.; Takano, Y.; He, Cenlin; Yang, P.; Leung, Lai-Yung R.; Gu, Y.; Lee, W- L.

A stochastic approach to model the positions of BC/dust internally mixed with two snow-grain types has been developed, including hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine their single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), internal mixing absorbs more light than external mixing. The snow-grain shape effect on absorption is relatively small, but its effect on the asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions of BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2 – 5 um) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4 um, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo more than external mixing and that the snow-grain shape plays a critical role in snow albedo calculations through the asymmetry factor. Also, snow albedo reduces more in the case of multiple inclusion of BC/dust compared to that of an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization containing contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountains/snow topography.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1172450
• Report Number(s): PNNL-SA-101022; KP1703020
• Journal Information: Journal of Geophysical Research. D. (Atmospheres), 119(12):7616–7632, Journal Name: Journal of Geophysical Research. D. (Atmospheres), 119(12):7616–7632
• Country of Publication: United States
• Language: English

Related Subjects

climate models
light absorption
mixed BC/dust
parameterization
snow grains
stochastic