Water Vapor Transport Across an Arid Sand Surface-Non-Linear Thermal Coupling, Wind-Driven Pore Advection, Subsurface Waves, and Exchange With the Atmospheric Boundary Layer - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Geophysical Research: Earth Surface Année : 2022

Water Vapor Transport Across an Arid Sand Surface-Non-Linear Thermal Coupling, Wind-Driven Pore Advection, Subsurface Waves, and Exchange With the Atmospheric Boundary Layer

M. Y. Louge
  • Fonction : Auteur correspondant
Alexandre Valance
Patrick Chasle

Résumé

Although vapor exchanged across hyper-arid surfaces without free liquid affects the water budget of sand seas, its mechanism is poorly documented for want of accurate instruments with fine spatial resolution. To rectify this, we report bulk density profiles and spatiotemporal variations of vapor mass fraction just below the surface of a mobile dune, acquired with a multi-sensor capacitance probe sensitive to tiny water films adsorbed on sand grains. We also record wind speed and direction, ambient temperature and relative humidity, net radiation flux, and subsurface temperature profiles over 2 days. The data validate a non-linear model of vapor mass fraction. Unlike heat, which conducts through grains, vapor percolates across the interstitial pore space by advection and diffusion. On time scales longer than evaporation, adsorbed films equilibrate with their surroundings and hinder molecular diffusion. Their non-linear coupling with subsurface temperature generates inflections in vapor profiles without counterpart in simpler diffusive systems. Pore advection arises as wind induces subtle pressure variations over the topography. During periods of aeolian transport, flowing sand dehydrates the surface intermittently, triggering evanescent vapor waves of amplitude decaying exponentially downward on a characteristic length implying an adsorption rate governed by a kinetic-limited activated process. Finally, the probe yields diffusive and advective exchanges with the atmospheric boundary layer. During the day, their combined flux is smaller than expected, yet nearly proportional to the difference between vapor mass fraction at the surface and aloft. Under stabler stratification at night, or during aeolian sand transport, this relation no longer holds.
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Dates et versions

hal-03657541 , version 1 (14-10-2022)

Identifiants

Citer

M. Y. Louge, Alexandre Valance, J. Xu, Ahmed Ould El Moctar, Patrick Chasle. Water Vapor Transport Across an Arid Sand Surface-Non-Linear Thermal Coupling, Wind-Driven Pore Advection, Subsurface Waves, and Exchange With the Atmospheric Boundary Layer. Journal of Geophysical Research: Earth Surface, 2022, 127 (4), pp.e2021JF006490. ⟨10.1029/2021JF006490⟩. ⟨hal-03657541⟩
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