1. Comparison of snow microstructure models Richard Essery Anna Kontu, Samuel Morin, Martin Proksch, Mel Sandells MicroSnow2 Workshop, Columbia MD, 13 – 15 July 2015

2. Uses of microstructure in snow models Grain size, shape and surface area measures of snow are used in model representations of: thermal conductivity hydraulic permeability compactioncouple to thermodynamics erosion by wind albedo scattering of microwave radiation mechanical stability snow chemistry

3. Representations of microstructure in snow models Community Land Model (CLM), Oleson et al. 2010 www.cesm.ucar.edu/models/ccsm4.0/clm/CLM4_Tech_Note.pdf Crocus, Carmagnola et al. 2014 www.the-cryosphere.net/8/417/2014/ Met Office Surface Exchange Scheme (MOSES), Essery et al. 2001 www.metoffice.gov.uk/media/pdf/9/j/HCTN_30.pdf SNTHERM, Jordan 1991 https://webcam.crrel.usace.army.mil/SNTHERM/ SNOWPACK, Lehning et al. 2002 http://www.sciencedirect.com/science/article/pii/S0165232X02000733 Also empirical relationships between SSA and snow type and density Domine et al. (2007). J. Geophys. Res., doi:10.1029/2006JF000512

4. DescriptorsPredictorsProperties Model Grain size Shape Optical radius Bond size Temperature dT/dz Liquid water Density Optical Mechanical Hydraulic Thermal CLM Crocus MOSES SNTHERM Snowpack Microstructure in snow models

5. Error sources in grain size simulations microstructure process parametrizations parameter values thermodynamics driving data process parametrizations parameter values numerics coupling

6. Snow model layering

7. NoSREx IOA @ FMI ARC, Sodankylä

8. Snow temperature

9. Traditional and optical bulk grain sizes correlation 0.58 detrended correlation 0.03

10. Traditional and optical grain size profiles

11. Snow temperature profiles

12. Snow density profiles

13. Grain size and SSA simulations MOSES r = 0.06 CLM r = 0.41 SNTHERM r = 0.66 MOSES r = 0.32 CLM r = 0.53 SNTHERM r = 0.59 Eulerian layers, simulated snow temperatures

14. Grain size and SSA simulations CROCUS r = 0.46 MOSES r = 0.35 CLM r = 0.62 SNTHERM r = 0.67 CROCUS r = 0.57 MOSES r = 0.46 CLM r = 0.58 SNTHERM r = 0.60 Lagrangian layers, measured snow temperatures

15. Tentative conclusions and future directions