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Abstract Realistic computational simulations in different oceanic basins reveal prevalent prograde mean flows (in the direction of topographic Rossby wave propagation along isobaths; aka topostrophy) on topographic slopes in the deep ocean, consistent with the barotropic theory of eddy-driven mean flows. Attention is focused on the western Mediterranean Sea with strong currents and steep topography. These prograde mean currents induce an opposing bottom drag stress and thus a turbulent boundary layer mean flow in the downhill direction, evidenced by a near-bottom negative mean vertical velocity. The slope-normal profile of diapycnal buoyancy mixing results in downslope mean advection near the bottom (a tendency to locally increase the mean buoyancy) and upslope buoyancy mixing (a tendency to decrease buoyancy) with associated buoyancy fluxes across the mean isopycnal surfaces (diapycnal downwelling). In the upper part of the boundary layer and nearby interior, the diapycnal turbulent buoyancy flux divergence reverses sign (diapycnal upwelling), with upward Eulerian mean buoyancy advection across isopycnal surfaces. These near-slope tendencies abate with further distance from the boundary. An along-isobath mean momentum balance shows an advective acceleration and a bottom-drag retardation of the prograde flow. The eddy buoyancy advection is significant near the slope, and the associated eddy potential energy conversion is negative, consistent with mean vertical shear flow generation for the eddies. This cross-isobath flow structure differs from previous proposals, and a new one-dimensional model is constructed for a topostrophic, stratified, slope bottom boundary layer. The broader issue of the return pathways of the global thermohaline circulation remains open, but the abyssal slope region is likely to play a dominant role.
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This content will become publicly available on December 16, 2026
Haboobs on Slopes
Abstract The impacts of topographic slope on daytime haboob propagation speeds and dust lofting are examined along with how these impacts are modulated by surface roughness length. A suite of 20 idealized, large‐eddy simulations are run with varied linear topographic slopes and surface roughness lengths. It is found that on flat ground, greater surface roughness increases drag on haboobs and causes haboobs to dissipate faster, thereby decreasing both haboob propagation speeds and dust lofting. In simulations with sloped topography, upslope anabatic winds form due to solar heating. As topographic slope and surface roughness are increased, the anabatic winds become faster. Greater surface roughness causes more drag on the anabatic wind, but this is counteracted by greater sensible heat fluxes driving a stronger pressure gradient. These anabatic winds act to advect haboobs upslope. Hence, as the topographic slope is increased, downslope haboob propagation speeds are decreased, and upslope haboob propagation speeds remain mostly unchanged. Anabatic winds act to loft dust as well leading to increased dust lofting jointly by the haboob and anabatic winds as topographic slopes are increased.
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- Award ID(s):
- 2029611
- PAR ID:
- 10679604
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 23
- ISSN:
- 2169-897X
- Page Range / eLocation ID:
- e2025JD044043
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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