Effect of snow grain shape and impurities on snow albedo and its parameterization: China, North America, and the Arctic

• Main Author: Dang, Cheng
• Other Authors: Warren, Stephen G, Fu, Qiang
• Format: Thesis
• Language: English
• Published: 2017
• Subjects: Albedo; Light-absorbing particles; Parameterization; Snow; Snow grain shape; Atmospheric sciences; Arctic; albedo; black carbon
• Online Access: http://hdl.handle.net/1773/38572

Thesis (Ph.D.)--University of Washington, 2017-03 Snow cover is important for Earth’s surface energy budget, primarily because the surface reflectance (albedo) is greatly increased if covered by a layer of snow. A correct estimation of snow albedo is therefore crucial for studying climate and snow hydrology. Snow albedo is influenced by many factors including snow depth, snow grain size, solar zenith angle, cloud cover, and light-absorbing particles (LAPs, black carbon, organic carbon, and mineral dust) in snow, and snow albedo is usually obtained from radiative transfer calculations. Therefore, an error in those factors and assumptions used in radiative transfer calculations could introduce errors in the computed snow albedo. This dissertation presents three separate works related to snow albedo, aiming towards a better understanding and quantification on the impact of different factors on snow albedo. First, a new parameterization method for narrowband and broadband albedo of pure snow and snow containing black carbon and mineral dust is introduced. Spectral albedo of snowpacks with different grain radii (5 – 2500 μm), containing a wide range of black carbon or mineral dust amounts (mixing ratio of 0 to 1) were calculated using radiative transfer models (DISORT). For each case, three broadband albedos (visible, near-IR, and all-wave) and twelve narrowband albedos (RRTM bands 2-13) are calculated and parameterized as functions of snow grain radius and LAP concentrations. This method can be incorporated into climate models to calculate snow albedo or study the impact of LAPs on snow albedo. Second, the effect of snow grain shape on snow albedo is studied. Radiative transfer calculations on snow albedo have usually assumed a spherical shape for snow grains, using Mie theory to calculate the single-scattering properties of ice spheres. The scattering by more realistic non-spherical grains is less in the forward direction and more to the sides. Incident sunlight scattered in the forward direction travels a longer ...