Wednesday, 12 January 2000: 8:00 AM
Ina Tegen, Columbia Univ. and NASA/GISS, New York, NY; and R. Miller and J. Perlwitz
.Soil dust aerosol is emitted from desert surfaces as well as from soil
surfaces that have been disturbed by human impact, like overgrazing
and agriculture in semi-arid regions, or by deforestation. Since the
atmospheric loading of soil dust can be very high, it is expected to
impact climate at least regionally. And since the magnitude of dust
deflation depends on climate variables like precipitation and wind
speed, feedback processes between dust production and climate need to
be taken into account to understand the impact of dust on the climate.
To study the sensitivity of the climate to soil dust forcing and
feedback of dust forcing upon dust production and transport, dust
needs to be included as dynamic and radiatively interactive tracer in
the GISS GCM. To assess the sensitivity of the climate response to
dust radiative properties (which is not very well known on the global
scale), the GCM was integrated using different dust single scattering
albedos, and in a control case dust was included as dynamic tracer
without interaction with radiation. These integrations were carried
out with fixed sea surface temperature as well as mixed layer ocean as
boundary conditions.
The results show that soil dust radiative forcing generally causes a
negative feedback on atmospheric dust loads, i.e. a reduction in the
dust load corresponding to a decrease in dust source flux. This
reduction varies both with the season and with the single scattering
albedo of the dust, depending on the region where dust deflation takes
place. The climate response and dust feedback to dust forcing turns
out to be highly sensitive to the dust single scatter albedo. Also,
the results indicate areas, where changes in dust deflation is
controlled by changes in surface winds, and those areas, where dust
deflation is controlled by changes in the hydrological cycle.
Discrepancies of the model results with observed interannual
variations in dust loads can indicate regions, where dust deflation
was additionally influenced by changes in soil surface conditions
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