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| Titel |
Aerosol direct radiative effect on solar radiation on planetary scale based on 7-year spectral aerosol optical properties from MODIS |
| VerfasserIn |
C. D. Papadimas, N. Hatzianastassiou, C. Matsoukas, I. Vardavas |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028892
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| Zusammenfassung |
| Atmospheric aerosols, both natural and anthropogenic, can cause climate change through
their direct, indirect and semi-direct effects on the radiative energy budget of the
Earth-atmosphere system. However, the quantification of the aerosol effects is difficult
because aerosol physical, chemical and optical properties are highly variable in space and
time. Another difficulty is the lack of continuous and long-term measurements of aerosol
properties.
In the present study the mean monthly direct radiative effect (DRE) of aerosols on solar
radiation is estimated on global scale for a 7-year period (March 2000 - February
2007), by using a deterministic spectral radiation transfer model and long-term
satellite spectral aerosol data. The model uses climatological input data for various
surface and atmospheric parameters, taken from the International Satellite Cloud
Climatology Project (ISCCP-D2), the National Centers for Environmental Prediction –
National Center for Atmospheric Research (NCEP-NCAR) Global Reanalysis project,
and other global data bases. The aerosol DRE computations are performed in the
ultraviolet, visible and near-infrared, spanning the total shortwave (SW) spectral range
0.2–10 μm. The model computes the aerosol effect on the SW radiation budget of the
Earth-atmosphere system, namely at the top of atmosphere (TOA reflected solar radiation),
within the atmosphere (absorbed solar radiation), and at the surface (incoming and
absorbed solar radiation). The multiyear global distributions of spectral aerosol optical
properties (aerosol optical depth, AOD, asymmetry parameter, gaer, and single
scattering albedo, Ïaer), which are of primary importance for aerosol DREs, are taken
from the MODerate resolution Imaging Spectroradiometer (MODIS) of NASA
(National Aeronautics and Space Administration) and they are supplemented by the
Global Aerosol Data Set (GADS). More specifically, we use MODIS AOD and gaer
data at 7 wavelengths extending from 470 to 2130 nm, over land and ocean. The
computations of aerosol DREs are performed at a spatial resolution of 2.5ºx2.5º
latitude-longitude.
According to the model results, the 7-year global mean aerosol direct radiative effect on
the outgoing (reflected) SW radiation at TOA (DRETOA) is equal -2.88 W/m2, indicating
thus a significant planetary cooling. At the regional scale, however, the cooling
effect is much stronger, while a planetary warming is found over highly reflecting
surfaces like deserts. The global effect of aerosols on the atmospheric absorption
of SW radiation (DREatmab) is equal to 3.94 W/m2, indicating an atmospheric
warming due to aerosols. In addition, aerosols are found to decrease the downward SW
radiation at the Earth’s surface (ÎFSurfDown) by -7.97 W/m2, producing thus a
very important surface radiative cooling. Based on the model computations, the
inter-annual change of aerosol DRE from 2000 to 2007 is -3.7% for DRETOA (less
aerosol planetary cooling), -13.4% for DREatmab (less aerosol atmospheric warming)
and -10.4% for DREsurf (less aerosol surface cooling). Our results indicate that a
significant reduction in the magnitude of aerosol radiative effects has taken place
from 2000 to 2007, which is primarily due to a corresponding decrease in aerosol
loads over many world regions, Asian, European and American countries included. |
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