The role of surface energy fluxes in pan-Arctic snow cover changes

Abstract

We analyze snow cover extent (SCE) trends in the National Oceanic and AtmosphericAdministration’s (NOAA) northern hemisphere weekly satellite SCE data using theMann–Kendall trend test and find that North American and Eurasian snow cover in thepan-Arctic have declined significantly in spring and summer over the period of satelliterecord beginning in the early 1970s. These trends are reproduced, both in trend directionand statistical significance, in reconstructions using the variable infiltration capacity (VIC)hydrological model. We find that spring and summer surface radiative and turbulent fluxesgenerated in VIC have strong correlations with satellite observations of SCE. We identifythe role of surface energy fluxes and determine which is most responsible for the observedspring and summer SCE recession. We find that positive trends in surface netradiation (SNR) accompany most of the SCE trends, whereas modeled latent heat(LH) and sensible heat (SH) trends associated with warming on SCE mostlycancel each other, except for North America in spring, and to a lesser extent forEurasia in summer. In spring over North America and summer in Eurasia, the SHcontribution to the observed snow cover trends is substantial. The results indicate thatΔSNR is the primaryenergy source and ΔSH plays a secondary role in changes of SCE. Compared withΔSNR andΔSH,ΔLH has a minor influence on pan-Arctic snow cover changes.