Introduction - Mineral Dust: A Key Player in the Earth System - page 6

research on the cryosphere, land surface, vegetation, marine ecosystems and human
activity, to name a few. In many ways dust is a topic par excellence for this evolving
research area, as it depends on and interacts with several spheres of the Earth
system: originating from the land surface, dust sources depend on geological and
geomorphological processes such as weathering and sediment transport (Chap. 3 ) .
On shorter timescales, vegetation, soil moisture and snow cover play a role, which
in turn depend on precipitation and temperature (Chap. 5 ) . Meteorology has a
strong control on dust emission and distribution through the generation of deflating
winds near the surface (Chap. 6 ) , as well as through vertical mixing and long-
range horizontal transport (Chap. 7 ) , through alterations during suspension (Chap.
4 ) and finally through dry and wet deposition processes (Chap. 8 ) , the former
depending again on the land surface and vegetation. Once airborne, dust can change
the radiation budget (Chap. 11 ) , the properties of clouds and precipitation (Chap.
12 ) and thus regional circulations (Chap. 13 ) , with potential feedbacks on the land
surface. Many of these processes crucially depend on the size distribution and
composition of the dust particles (Chap. 2 ) . Dust depositions into the ocean and
on land potentially fertilise ecosystems and impact on the carbon cycle (Chap. 14 ) ,
which then feeds back on climate. Dust depositions on ice and snow change the
albedo and can therefore affect melting rates. Such depositions together with those
in soils, lakes and oceans are increasingly used to reconstruct past climates (Chaps.
16 , 17 , 18 ) . Last but not least, it is still a topic of debate to what extent human
activities (land-use change, agriculture, stock grazing, mining, off-road transport,
etc.) have changed and will change the distribution, strength and characteristics
of dust sources. This has potential ramifications for the quality of life in affected
regions through respiratory and eye diseases (Chap. 15 ) and reduced visibility.
In contrast, there is growing evidence that airborne dust reacts chemically with
anthropogenically emitted substances, which contributes to an ageing of natural
particles, changing their optical and microphysical properties (Chap. 4 ) .
In addition to its prominent role in Earth system science, several new develop-
ments in dust research itself have contributed to the rapidly growing interest in this
topic. Dust is a quantity that is difficult to observe in situ, particularly near source
regions, which tend to be remote and inaccessible due to harsh climate conditions,
the lack of infrastructure and even political instability. Therefore the advance of
spaceborne remote-sensing capabilities has allowed fascinating new insights into
the distribution and characteristics of atmospheric dust (see Chap. 7 ) . Several new
developments are particularly noteworthy (in rough order of occurrence):

￿ The Multi-angle Imaging SpectroRadiometer (MISR) onboard the Terra satellite

became operational in February 2000. Its innovative configuration of nine
separate digital cameras, which gather data in four different spectral bands of
the solar spectrum, allowed for the first time to view the same dust plume from
different angles. This makes it possible to retrieve a plume height together with
aspects such as optical thickness, a-sphericity of particles and optical properties
(Kalashnikova et al. 2005 ).