Understanding Recent Snow Cover Changes in the Pan-Arctic.

摘要

Over the pan-Arctic land area, surface air temperature (SAT) has risen by almost twice the global average in recent decades, and many other changes have been observed across the region, indicating a system-wide response to a changing climate. These changes motivate this study, the goal of which is to identify the roles of hydroclimate indicators in snow cover extent (SCE) changes, and to evaluate the impact of snow cover recession on frozen soil heat content (SHC) over the pan-Arctic land region. I do so by exploring the variability and trends in surface energy fluxes, SCE and SHC, as well as their corresponding correlations. This work comprises four related studies. First, high latitude surface radiative fluxes produced by a suite of satellite, global reanalysis, and land surface model-derived data were compared with in situ observations. The results show that relative to other data sources, the Variable Infiltration Capacity (VIC) land surface model provides good estimates of surface radiative fluxes. Second, the relative roles of surface energy fluxes in the observed spring and summer SCE recession were identified. My analyses indicate that surface net radiation (SNR) provides the primary energy source and sensible heat (SH) plays a secondary role in observed changes of SCE. Compared with SNR and SH, latent heat has only a minor influence on snow cover changes. Third, by comparing with the corresponding satellite product, the ability of VIC to reconstruct spatial and temporal changes of SCE was assessed. The relationships between snow cover and hydroclimate changes over each snow cover sensitivity zone (SCSZ) for North America and Eurasia were also identified. We find that VIC is able to reconstruct spatial and temporal changes of observed SCE, and the snow cover recession is mainly driven by statistically significant decreases in snow surface albedo and increased SAT, as well as statistically significant increased atmospheric water vapor pressure. Finally, I explored the effects of snow cover recession and increases in SAT on SHC. I found that increasing SAT during late spring and early summer has the greatest influence on SHC changes, and reduced SCE plays a secondary role, which is only significant in SCSZ.