Modeling Gas Flow Velocities in Soils Induced By Variations in Surface Pressure, Heat and Moisture Dynamics

Atmospheric pressure is constantly moving air in, out and through the surface of the soil or a snowpack. This pressure pumping (or ventilating) mechanism influences soil water evaporation and snow sublimation, the fluxes of key climate-warming greenhouse gases, and rate at which contaminants can be removed from soils. Therefore, the ability to model pressure pumping effects through these two media is relevant to many current environmental concerns. The present study discusses the differences between the two broad categories of pressure pumping models (one that assumes the flow field is compressible and the other incompressible) and points out that these models predict very different ventilation rates. To compare the performance of these two different model types several days of measured 1 Hz pressure fluctuations (along with measured soil temperature and moisture data) are used to drive these models. Results indicate that the two model types respond differently when pressure changes are influenced by changes in soil temperature and moisture, with the compressible model suggesting that dynamic soil temperature and moisture effects are small, in agreement with expectations, and the incompressible suggesting that they can cause surprisingly large effects. Present results also identify (for the first time) meso-scale atmospheric inertia-gravity waves and solitons, often associated with frontal systems, convective activity and rain, as significant drivers of pressure induced gas exchange.