Event Detail

Event Type: 
Applied Mathematics and Computation Seminar
Friday, October 26, 2007 - 05:00
Gilkey 113

Speaker Info

OSU Crop and Soil Science

It has been known for many years that soil cracks enhance drying of the soil matrix. In addition, salt crusting on fracture walls indicates evaporation rates from within fractures that are much higher than can be accommodated with the traditional diffusive venting mechanism. Agricultural field and laboratory experiments over the past 60 years quantified the magnitude of drying in the vicinity of cracks, and under various conditions (e.g., wind, radiative heating, crack aperture). As a result of this work, agricultural practices were developed to ameliorate the negative effects of cracks on crop productivity. However, during those 60 years, no mechanism was suggested for the cause of enhanced drying. Recently we proposed that convection of fracture/crack air is the key mechanism driving the enhanced drying process. Each wall forming the crack maintains thermal boundary conditions with a vertical thermal gradient that oscillates diurnally. Convective venting occurs at night when either the vertical thermal gradient within the crack is significantly unstable (Rayleigh-Bernard instability) or when the density gradient at the atmosphere boundary permits entrainment of cooler (and usually drier) atmospheric air (Rayleigh-Taylor instability), thus generating invasive fingers of cooler atmospheric air. I will present the characteristics of the mechanism, the range of parameters that are realistic for natural settings, and field evidence for the existence of this mechanism in a natural rock fracture. The problem is yet to be solved numerically.