Understanding Heat Transfer in the Shallow Subsurface Using Temperature Observations

Abstract

In this study, we analyzed the potential of distributed soil temperature and soil moisture observations for identifying the spatiotemporal variability of near‐surface water and energy fluxes. We studied the soil energy balance using soil moisture and temperature data collected during the Second Microwave Water and Energy Balance Experiment (MicroWEX‐2) in Florida. We found that heat transfer in the shallow subsurface could not be explained by conduction. Sinks and sources of energy in each soil layer were quantified using an inversion approach to the heat diffusion equation. We investigated the extent to which the sinks and sources could be explained by advection and phase change. From our analysis, it seems that, for dry days, advection is a comparatively minor contributor to heat transfer and that phase change plays a more significant role. Yet vapor diffusion rates, required for sustaining phase changes and thus evaporation in the soil large enough to explain the sinks and sources, were beyond the plausible range. We concluded that soil moisture and temperature observations can yield quantitative information on the surface energy balance and heat partitioning. There is a lack of understanding of heat transfer in the shallow subsurface, however, that hampers the translation of soil temperature and moisture observations to water and energy fluxes.