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Thermal Conduction
Heat fluxes at the snow/soil interface include thermal conduction, vapor diffusion, and
convection from free air and flow water (Chung et al., 2006). Figure 6 shows the thermal
conduction fluxes, with an average difference between two models of 1.43 W/m 2 for late winter
(IOP3) and 0.06 W/m 2 for early spring (IOP4). The daily oscillation was less dramatic in early
spring than in late winter since the temperature differences at the interface was less significant in
early spring (soil and snow both thawed). This suggests that soil conduction is predominant in the
soil heat contribution to the snowpack.
Figure 6. Simulated soil heat fluxes at the snow/soil interface over the study period.
Diffusion and Convection
SNTHERM only considers thermal conduction from the soil. Vapor diffusion from the soil and
natural convection of free air in snow are unique to SSVAT. On average, vapor diffusion and
natural convection were 10 –7 times smaller than thermal conduction at the interface (Fig 7). Vapor
diffusion displayed a diurnal cycle in late winter because it was affected by the diurnal
temperature cycle. Natural convection of free air in snow was significant in early spring,
especially on DOY 87–88. Comparing Fig 5 with Fig 7, air convection may be responsible for the
increasing variability of the heat content in snow on DOY 87–89. This suggests the importance of
convection in snow may exceed that of vapor diffusion or the thermal conduction.
Figure 7. Simulated heat fluxes at the snow/soil interface over the study period.
Air Convection
Fig 8 shows the occurrence of air convection in a snowpack in late winter (IOP3) and early
spring (IOP4). Red color and black color represented the occurrence of the air convection whereas
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