Release Level	6.0
	Release Date	2011 10
	Revision Level	1.0

Last modified on:   Saturday, 15-Oct-11 19:35 CEST

Dust entrainment: wind erosion

The dust entrainment model estimates non-pyrogenic dust emission from natural surfaces as a function of wind speed, lans cover/vegetation, soil characteristics, and soil moisture, primarily.

The total Dust PM10 emission [g/s/ha] is calculated as the product of

1. WindFactor,
2. ErosionFactor (erodibility)
3. CalibrationFactor.

The Calibration factor

is a user defined multiplier, that should be made part of a data assimilation scheme to minimize overall bias.

The Wind factor

is computed from average hourly (monitored ar generated by MM5) ground level wind speed (m/s) using a Weibull function to generate a distribution of wind speeds v and their relative frequency around that mean, as follows:

for v>TR: f(v) = (v - TR) **EXP
for v<TR: f(v) = 0
where TR is the (user-defined) Wind Threshold,
and EXP is the (user-defined) Exponent
windFactor = sum over all frequency classes of ( f(v)*frequency(v) )
frequency(v) = (k/c) * pow( (v/c), (k-1) ) * exp( -pow( (v/c), k) )
where v is the wind speed, k is the shape parameter, c is the scale parameter of the Weibull distribution.

A user defined multiplier can be used to scale the original, hourly average wind speed.

The Erosion factor

depends on:

• land use (e.g., CORINE classification)
• FAO soil type (that defines the fractions of coarse (sand)a medium (silt) and fine (loam) soil components,
• slope, orientation (aspect) and gradient,
• soil moisture, and in conjunction with drying/recently dried soils, saltation as a mechanical process to break up the crust and thus increase erodibility.

  Land use classification This is either based on an NDVI value directly obtained from satellite imagery (e.g., MODIS); or estimated from the predomint land use class. Each land use class has a range of possible NDVI values assigned, the default NDVI value is the arithmetic mean from the interval: CORINE: available for Europe only (an alternative classification scheme for outside Europe can be based on the global US Geological Survey (USGS) land use data set REFERENCE ? Landuse class NDVI min NDVI max 111 - Continuous urban fabric 0.00 2.00 131 - Mineral extraction sites 8.00 10.00 141 - Green urban areas 0.00 3.00 331 - Beaches - dunes - sands 8.50 01.00 333 - Sparsely vegetated areas 6.50 8.50 The land-use defines a range of possible NDVI values (between 0 and 10), that can be configured by a separate land use NDVI editor.

  FAO soil types: Available globally at a resolution of ?????. defined by sand (coarse), silt (medium), and loam (fine, heavy) percentage; The three fraction have their individual wind thresholds for erosion, loam and sand fraction are responsible for crust formation and saltation processes, respectively (not yet implemented). Soil type sand silt loam Bk35-2/3abA 0 50 50 Be117-2/3bc 0 65 35 I-Bk-E-c 0 100 0 Lv7-3ab 0 60 40 Vc58-3ab 0 70 30

  Soil moisture

  the effect of soil moisture is described as a simple linear treshold function:

  soil moisture > THRESHOLD (e.g., 80 % of field capacity) => sm_factor = 0
  soil moisture < THRESHOLD => sm_factor = (THRESHOLD (in %) - soil_moisture) * 2

  A user defined soil moisture multipier can be used to adjust any observed soil moisture data.

  Drying soils, crusts and the saltation factor

  Depending on composition (loam component) drying soild will form a crust that limts erodibility. Depnding on the coarse sand fraction, and the time/wind exposure since drying (to or below the soil moisture threshold) this crust will be broken through the process of saltation, which will increase erodibility asymptotically to its default value corresponding to the actual soil moisture.

  The corresponding correction factor is a linear function of "wind-hours" above a saltation threshold.

  Deposition, loss and re-entrainment

  Particulates are deposited on all surfaces, and depending on a surface specific loss term, available for re-entrainment. The loss factor is applied once, at the hour of deposition. The remaining mass accumulates until the wind exceeds the threshold in any one of the speed clases and the wind factor > 0.0.

  The loss coefficient is a function of land cover, 100% for open water. The loss factor is one of the properties defined in the land cover parameter table.

  Re-entrainment from depositied dust is limited to the accumulated deposition, corrected by a land cover (surface) specific loss factor.