Dating Quaternary alluvial fans with morphologic methods based on hillslope diffusion

1

Dust-model upscaling from plot scale to global
scale

• Challenge
• To provide large-scale models with estimates for
  z0, u, and dispersion that reflect small-scale
  BL processes and surface characteristics.

• Two basic approaches
• Run global models in a nested, or multi-grid,
  framework.
• Provide global models with a database of
  high-resolution boundary-layer model results to
  use as lookup tables.

Paula Helm USGS
Vegetation cover changes through El Nino-La Nina
cycles, Yuma AZ
2

Application Topographic shielding with analytic
solutions

u/u0
Owens Valley, CA 30m USGS DEM
0.0 2.0
Analytic solutions provided by Jackson and Hunt
(1975), wind from the south.
3

A hierarchy of boundary-layer models

• Analytic solutions for flow over low hills,
  augmented by separated-flow regions (Jackson and
  Hunt).
• Computationally fast (uses FFTs), but only
  approximate.
• Numerical solutions to Reynolds stress equations
  (mean turbulence) with turbulent closure (e.g.
  MSFD model).
• Higher-order effects included.
• Large-Eddy Simulations Direct Numerical
  Simulations

4

Application Mom. part. over vegetated surfaces
w/ MSFD

u/u0
0.0 1.0 2.0
MSFD model run over surfaces with different
heights, densities, and spatial distributions
(regular vs clustered).
5

Application Effects of vegetation on surface
roughness

Using individual-plant map, aggregate data at
coarser scale, calculate density, cluster index,
and use forward models to map effective z0
Vidal Valley, CA color DOQQ
Map of individual plants
6

Application Effects of vegetation on surface
roughness

z0
u/u0
0.005 0.05
0.1 1.0
In this way, the effects of vegetation changes
can be incorporated from plant scale to basin
scale.
7

Application Sub-grid scale dispersion

With Fourier-transform framework, localized and
distributed sources can be calculated with equal
ease.
8

Application High-res emission and dispersion in
Phoenix, AZ

cgr,sand
Landsat-derived land cover, Phoenix, AZ
0.0 1.0
Analytic solutions for advection, dispersion, and
settling can be used to improve sub-grid
transport fate, especially for coarse particles.
9

Active Interests/Projects

• Boundary-layer modeling of the effects of
  small-scale topography and vegetation on dust
  emissions
• Water-table dynamics and their influence on dust
  emissions from playas (w/ USGS Earth Surface
  Processes)
• Using soil AV horizons as dust-deposition
  indicators over geologic time