 |
| Titel |
Aerosol direct effect on solar radiation over the eastern Mediterranean Sea based on AVHRR satellite measurements |
| VerfasserIn |
Paraskevi Georgakaki, Christos D. Papadimas, Nikos Hatzianastassiou, Aggeliki Fotiadi, Christos Matsoukas, Paul Stackhouse, Maria Kanakidou, Ilias M. Vardavas |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250153395
|
| Publikation (Nr.) |
 EGU/EGU2017-18367.pdf |
|
|
|
|
|
| Zusammenfassung |
| Despite the improved scientific understanding of the direct effect of aerosols on solar
radiation (direct radiative effect, DRE) improvements are necessary, for example regarding
the accuracy of the magnitude of estimated DREs and their spatial and temporal variability.
This variability cannot be ensured by in-situ surface and airborne measurements, while it is
also relatively difficult to capture through satellite observations. This becomes even more
difficult when complete spatial coverage of extended areas is required, especially
concerning areas that host various aerosol types with variable physico-chemical
and optical aerosol properties. Better assessments of aerosol DREs are necessary,
relying on aerosol optical properties with high spatial and temporal variation. The
present study aims to provide a refined, along these lines, assessment of aerosol
DREs over the eastern Mediterranean (EM) Sea, which is a key area for aerosol
studies.
Daily DREs are computed for 1˚ x1˚ latitude-longitude grids with the FORTH detailed
spectral radiation transfer model (RTM) using input data for various atmospheric and surface
parameters, such as clouds, water vapor, ozone and surface albedo, taken from the
NASA-Langley Global Earth Observing System (GEOS) database. The model spectral
aerosol optical depth (AOD), single scattering albedo and asymmetry parameter are taken
from the Global Aerosol Data Set and the NOAA Climate Data Record (CDR) version 2 of
Advanced Very High resolution Radiometer (AVHRR) AOD dataset which is available
over oceans at 0.63 microns and at 0.1˚ x0.1˚ . The aerosol DREs are computed
at the surface, the top-of-atmosphere and within the atmosphere, over the period
1985-1995.
Preliminary model results for the period 1990-1993 reveal a significant spatial and
temporal variability of DREs over the EM Sea, for example larger values over the Aegean and
Black Seas, surrounded by land areas with significant anthropogenic aerosol sources, and
over the southernmost parts of EM Sea, affected by frequent Saharan dust export. The mean
regional annual AODs range from 0.17±0.05 to 0.23±0.06. The corresponding regional
annual DREs at surface range from -14±3 to -18±4 W/m2 (surface radiative cooling), while
in the atmosphere they vary between 7±2 and 10±2 W/m2 (atmospheric heating), yielding a
planetary cooling above the EM Sea between -6±1 and -8±2 W/m2. However, these AOD
and DRE values vary depending on the criteria of data spatial and temporal availability
applied in the AOD and DRE calculation, because of the limited availability of
retrieved AVHRR AOD over specific areas and in specific days. The DREs reach larger
magnitudes at pixel-level; for example the surface DREs slightly exceed -30 W/m2,
whereas they take larger values (magnitudes larger than -50 W/m2 in summer) when
computed on a monthly basis, and even larger values on daily basis. The model results
underline the high spatial and temporal variability of aerosol DREs, and the care that
must be taken when averaging over space and time. It also points to the need for
availability of aerosol data with concurrent high spatial and temporal coverage
and resolution, which should be sought in ongoing and future satellite missions. |
|
|
|
|
|
|