Spatiotemporal distribution of seasonal snow density in the Northern Hemisphere based on in situ observation

The snow density is a fundamental variable of the snow physical evolution processes, which can reflect the snowpack condition due to the thermal and gravitational compaction. Snow density is a bridge to transfer snow depth to snow water equivalent (SWE) for the snow water resources research. Therefore, it is important to understand the spatiotemporal distribution of snow density for the appropriate estimation of SWE. In this study, in situ snow densities from more than 6000 stations in the Northern Hemisphere were used to analyze the spatial and temporal variations in snow density. The results displayed that snow density varied spatially and temporally in the Northern Hemisphere, with range of below 0.1 to over 0.4 g/cm 3 . The average snow densities in the mountainous regions of western North America, southeastern Canada, and Europe range from approximately 0.24 to 0.26 g/cm 3 , which is significantly greater than the values of 0.16 to 0.17 g/cm 3 observed in Siberia, central Canada, the Great Plains of the United States, and China. The seasonal growth rates also present large spatial heterogeneity. The rates are over 0.024 g/cm 3 per month in Southeastern Canada, the west mountain of North America and Europe, approximately 0.017 g/cm 3 per month in Siberia, much larger than approximately 0.004 g/cm 3 per month in other regions. Snow cover duration is a critical factor to determine the snow density. This study endorses the small snow density in China based on meteorological station observations, which results from that the meteorological stations are dominantly distributed in plain areas with relative short snow cover duration and shallow snow.