Dust Production Mechanisms - Mineral Dust: A Key Player in the Earth System - page 92

Chapter 5
Dust Production Mechanisms
Beatrice Marticorena
Abstract This chapter is concerned with dust production mechanisms, that is, the
interactions between the wind and the surface that lead to the emission of fine soil
particles. Mineral dust emissions mainly result from wind erosion in the arid and
semi-arid regions of the world. Wind is thus the main driver of emissions, but
surface characteristics also play a key role for their spatial distribution, intensity
and frequency. This chapter describes the main stages involved in dust emission:
the erosion threshold, the saltation flux and the dust production by sandblasting,
with a focus on the influence of the surface characteristics. For each of these stages,
the involved physical processes and their parameterisations are described with a
discussion on their limitations. The first stage, the erosion threshold, corresponds to
the minimum wind velocity that must be reached for the initiation of soil particle
movement. This threshold depends on the soil properties (size distribution and
moisture) and surface roughness. It is a key parameter for dust emission, since
it controls the frequency of dust emission events. The horizontal motion of soil
particles close to the surface is mainly a saltation motion, where soil particles
rebound on the surface and initiate the movement of other soil particles. These
rebounds also lead to the ejection of fine dust particles from the surface or the
saltating aggregates, which correspond to the sandblasting process. Recent field
measurements show that saltation is a prerequisite for intense dust emissions. While
the erosion threshold and the saltation flux are well understood and reasonably
quantified, the amount and size of the dust emitted by sandblasting and their
dependence on soil properties and wind intensity are still insufficiently described
to provide reliable parameterisations. Significant progresses in the description and
parameterisation of dust emission processes have been achieved in the last 20 years,
which allow a better understanding of the properties that makes specific areas active