Geoscience Reference
In-Depth Information
20
Desert dust
Richard Washington and Giles S. F. Wiggs
20.1
Introduction
(research campaigns, number of researchers, papers pub-
lished) it is perhaps a field that has advanced further than
any other in the arid zone realm. Two key drivers have
been responsible for this. First, the availability of long-
term satellite-derived atmospheric dust data sets has al-
lowed the first near-global perspective on dust to emerge.
Second, recognition of the importance of dust in the Earth
System, particularly in terms of the interaction of dust
with the planetary radiation budget, has meant that rep-
resentation of the dust cycle in numerical models is crit-
ical in diagnosing and predicting the climate system at
timescales ranging from weather forecasting to the cli-
mates of future decades and centuries. At the same time,
deficiencies in the representation of dust in the models and
uncertainties in satellite retrieval have prompted aircraft
and ground-based campaigns to measure in situ dust emis-
sion, transport and deposition. As a result, considerable
resources and effort have been invested in investigating
dust processes and dynamics from the field scale to the
continental and global scale. This chapter therefore gives
prominence to new methods of dust measurement since
much of what we now know about dust at the global
scale has emerged from these tools and initiatives. Also
reviewed is the dramatic progress that has been made
with numerical modelling of dust and the current status
of knowledge on key dust source regions. The chapter
also covers dust transport and deposition and considers
the likelihood of changing global dust loads in the future.
Mineral dust is the most important export from the world's
arid zones to the global Earth System and is known to
affect atmospheric, oceanic, biological, terrestrial and hu-
man processes and systems, including:
Reduction in shortwave and absorption of longwave ra-
diation (Miller and Tegen, 1998; Milton
et al.
, 2008).
Interaction with cloud microphysics (Ansmann
et al.
,
2008).
Suppression of rainfall, e.g. in Sahel (Rosenfeld, Rudich
and Lahav, 2001; Hui
et al.
, 2008).
Modification of tropical storm and cyclone intensities
(Evan
et al.
, 2006).
CO
2
drawdown affecting ocean fertilisation (Jickells
et al.
, 2005; Cassar
et al.
, 2007).
Long-distance nutrient transport and vegetation fertili-
sation (e.g. Okin
et al.
, 2004; Koren
et al.
, 2006).
Human health and land use (e.g. O'Hara
et al.
, 2000;
Prospero
et al.
, 2008).
Agricultural soil erosion and productivity (Worster,
1979; Zobeck and Van Pelt, 2006).
20.1.1
Dust in a geomorphological context
Research on dust emissions from desert regions and its
distribution in the atmosphere has seen an enormous in-
crease in attention since the 2nd edition of
Arid Zone
Geomorphology
in 1997. In terms of research activity
20.1.1.1 Physical characteristics of dust
It is the fine texture of dust that augments its environ-
mental impacts. Aeolian dust derived from arid zones is
