Parameterization of single-scattering properties of snow

• Published in: The Cryosphere
• Main Authors: Räisänen, P., Kokhanovsky, A., Guyot, G., Jourdan, O., Nousiainen, T.
• Other Authors: Finnish Meteorological Institute (FMI), Institute of Environmental Physics Bremen (IUP), University of Bremen, Laboratoire de Météorologie Physique (LaMP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology; Ny-Ålesund; Svalbard; Ny Ålesund; The Cryosphere
• Online Access: https://hal.science/hal-01982587; https://hal.science/hal-01982587/document; https://hal.science/hal-01982587/file/Raisaneneetal.CLIMSLIPtc-9-1277-2015.pdf; https://doi.org/10.5194/tc-9-1277-2015

International audience Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications , single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat phase function typical of deformed non-spherical particles, this is still a rather ad hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius r vp. Parameterization equations are developed for λ = 0.199-2.7 µm and r vp = 10-2000 µm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function P 11 as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function pa-rameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons to spheres and distorted Koch fractals.