ENSO surface shortwave radiation forcing over the tropical Pacific

K. G. Pavlakis (1, 2, 3) , N. Hatzianastassiou (1, 4) , C. Matsoukas (1, 5) , A. Fotiadi (1, 3) , I. Vardavas (1, 3)

1 Foundation for Research and Technology-Hellas
2 Department of General Applied Science
3 Department of Physics
4 Laboratory of Meteorology [Ioannina]
5 Department of Environment [Mytilene]

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^?2 during El Niño episodes to +40 Wm^?2 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^?2 to ?20 Wm^?2 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.

Domaines: Océan, Atmosphère

K. G. Pavlakis, N. Hatzianastassiou, C. Matsoukas, A. Fotiadi, I. Vardavas. ENSO surface shortwave radiation forcing over the tropical Pacific. Atmospheric Chemistry and Physics Discussions, 2008, 8 (2), pp.6697-6728. ⟨hal-00304077⟩