Atmospheric Chemistry and Physics Discussions
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2008
10.5194/acpd-8-6697-2008
http://www.atmos-chem-phys-discuss.net/8/6697/2008/
http://www.atmos-chem-phys-discuss.net/8/6697/2008/acpd-8-6697-2008.html
http://www.atmos-chem-phys-discuss.net/8/6697/2008/acpd-8-6697-2008.pdf
6697
6728
2008-04-07
ENSO surface shortwave radiation forcing over the tropical Pacific
K. G. Pavlakis
N. Hatzianastassiou
C. Matsoukas
A. Fotiadi
I. Vardavas
Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece
Department of General Applied Science, Technological Educational Institute of Crete, Greece
Department of Physics, University of Crete, Crete, Greece
Laboratory of Meteorology, Department of Physics, University of Ioannina, Greece
Department of Environment, University of the Aegean, Greece
We have studied the spatial and temporal variation of the downward shortwave
radiation (DSR) at the surface of the Earth during ENSO events for a 21-year
period over the tropical and subtropical Pacific Ocean (40° S–40° N, 90° E–75° W).
The fluxes were computed using a deterministic model for atmospheric
radiation transfer, along with satellite data from the ISCCP-D2 database,
reanalysis data from NCEP/NCAR for the key atmospheric and surface input
parameters, and aerosol parameters from GADS (acronyms explained in main
text). A clear anti-correlation was found between the downward shortwave
radiation anomaly (DSR-A) time-series, in the region 7° S–5° N 160° E-160° W located
west of the Niño-3.4 region, and the Niño-3.4 index time-series. In
this region where the highest in absolute value DSR anomalies are observed,
the mean DSR anomaly values range from −45 Wm<sup>−2</sup> during El Niño
episodes to +40 Wm<sup>−2</sup> during La Niña events. Within the Niño-3.4
region no significant DSR anomalies are observed during the cold ENSO phase
in contrast to the warm ENSO phase. A high correlation was also found over
the western Pacific (10° S–5° N, 120–140° E),
where the mean DSR anomaly values
range from +20 Wm<sup>−2</sup> to −20 Wm<sup>−2</sup> during El Niño and La Niña
episodes, respectively. There is also convincing evidence that the time
series of the mean downward shortwave radiation anomaly in the north
subtropical Pacific region 7–15° N 150–170° E, precedes the Niño-3.4 index
time-series by about 7 months. Thus, the downward shortwave radiation
anomaly is a complementary index to the SST anomaly for the study of ENSO
events and can be used to assess whether or not El Niño or La Niña
conditions prevail.
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