A landsurface process/radiobrightness model with coupled heat and moisture transport for freezing soils

Phase change of water is an important sink and source of energy and moisture within soils as well as a significant influence upon soil temperature and moisture profiles. These profiles play a crucial role in governing energy and moisture fluxes between bare soils and the atmosphere. They also codetermine radiobrightness, so that the difference between modeled and observed radiobrightness becomes a measure of error in a model's estimate of temperature or moisture. In this paper, we present a physically based, coupledheat and moisturetransport, onedimensional hydrology/radiobrightness (1 dH/R) model for bare, freezing and thawing, moist soils that are subject to insolation, radiant heating and cooling, and sensible and latent heat exchanges with the atmosphere. We use this model to examine thermal, hydrologie, and Special Sensor Microwave/Imager (SSM/I) radiobrightness signatures for a threemonth, drydown simulation in the fall and winter of the northern United States Great Plains as part of an investigation of the effects of coupling heat and moisture transport. Given a typical initial moisture content of 38%, we find that coupled transport results in a reduction of ice in the surface soil by 21%. The range of diurnal variations in temperature are not significantly affected by coupled transport. Diurnal variations in the 19GHz, Hpolarized radiobrightness can be greater in the coupled transport case by 37 K. Total diurnal variation can exceed 57 K during periods of diurnal freezing and thawing.