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1. The sun is the earth`s energy source. Clip 1 demonstrates the way the sun`s electromagnetic radiation is distributed in our atmosphere: part of the energy is scattered in the air, while most of it reaches the surface. Then, some is absorbed and the rest is reflected back.
2. When aerosol particals are present in the atmosphere, they affect the way the photons behave. This is called the Direct radiative effect of aerosols in the atmosphere. In Clip 2 the aerosol blocks part of the energy, by absorbing it or reflecting it back to space, therefor lessening the energy flow to the earth, which means cooling the atmosphere and ground underneath.
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All the published estimates of the aerosol direct radiative forcing so far are done using models.
The only exception is a combination of CERES measurements of reflected solar flux and spectral
measurements of aerosol over the ocean,used by Loeb and Kato,[2002]to derive the aerosol
reflected sunlight (not anthropogenic forcing) in cloud free conditions using TRMM data over
the tropical region of the TRMM orbit.
To get the forcing one still needs to distinguish between
the natural and anthropogenic components.A summary of the modeled estimates is given in the
IPCC 2001 report,with a total direct forcing due to sulfates and organics of -0.5w/m
2
and that
due to black carbon of +0.2w/m
2
(we do not include here dust for which there is no central value,
only an error bar since it is still very difficult to estimate the anthropogenic component).
Hansen et al [2001]estimated the total forcing due to sulfates and organics of -1.3w/m
2
and
that due to black carbon of +0.8w/m
The differences between the estimates fit the large error
bars.One of the reasons for the large change in the black carbon absorption is the report by
Jacobson [2000]who, using a model, showed that black carbon is present mainly as an internal
mixture in the atmosphere and therefore its absorption is two to three times larger than in the
IPCC assumed external mixture.Measurements do affirm the predominance of internal mixtures
[Martins et al.,1998].
In this project we shall derive the aerosol direct forcing over most of the globe using
several pathways:
1)MODIS derived aerosol reflected spectral flux without pre-assumed angular
models for aerosol, and with high spatial resolution (500m),
2)using CERES with 20 km pixels,
assumed angular models but much better spectral accounting for reflected light than that of
MODIS,
3)using a measurement driven chemical transport model,
4)an integrated
climate/aerosol transport model and data assimilation system.
