SnowSTAR2002 transect reconstruction using a multilayered energy and mass balance snow model

The lateral and vertical variability of snow stratigraphy was investigated through comparison of measured profiles of snow density, temperature and grain size obtained during the SnowSTAR2002 1200-km transect from Nome to Barrow with model reconstructions from SNTHERM, a multilayered energy and mass balance snow model. Model profiles were simulated at the SnowSTAR2002 observation sites using ERA-40 reanalysis as meteorological forcing. ERA-40 precipitation was rescaled so that the total snow water equivalent (SWE) on the SnowSTAR2002 observation dates equaled the observed values. The mean absolute error (MAE) of measured and simulated snow properties shows that SNTHERM was able to provide good simulations for snowpack temperature, with larger errors for grain size and density. A spatial similarity analysis using semivariograms of measured profiles shows that there is diverse spatial and profile variability for snow properties along the SnowSTAR2002 transect resulting from differences in initial snow deposition, influenced by wind, vegetation, topography, and post-depositional mechanical and thermal metamorphism. The correlation length in snow density (42km) is quite low, whereas it is slightly longer for snow grain size (125km) and longer still for snow temperature (130km). An important practical question that the observed and reconstructed profiles allow to be addressed is the implications of model errors in the observed snow properties for simulated microwave emissions signatures. We used the Microwave Emission Model for Layered Snowpacks (MEMLS) to simulate 19 and 37 GHz brightness temperatures. Comparison of SNTHERM/MEMLS and SnowSTAR2002/MEMLS brightness temperatures showed a very good match occurs at 19 GHz (a root mean square error (RMSE) 1.5K for vertical polarization, increasing to 8.7K for horizontal polarization), and somewhat larger (5.9K for vertical polarization, and 6.2K for the horizontal polarization) at 37 GHz. These results successfully capture the variability along the transect and imply that simulation of snow microphysical profiles is a viable strategy for passive microwave satellite-based retrievals of SWE.