Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 6 2006 10.5194/acpd-6-12895-2006 http://www.atmos-chem-phys-discuss.net/6/12895/2006/ http://www.atmos-chem-phys-discuss.net/6/12895/2006/acpd-6-12895-2006.html http://www.atmos-chem-phys-discuss.net/6/12895/2006/acpd-6-12895-2006.pdf 12895 12928 2006-12-11 ENSO surface longwave radiation forcing over the tropical Pacific K. G. Pavlakis pavlakis@iesl.forth.gr D. Hatzidimitriou E. Drakakis C. Matsoukas A. Fotiadi N. Hatzianastassiou 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 Department of Electrical Engineering, Technological Educational Institute of 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 surface longwave radiation (downwelling and net) over a 21-year period in 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 and reanalysis data from NCEP/NCAR (acronyms explained in main text), for the key atmospheric and surface input parameters. An excellent correlation was found between the downwelling longwave radiation (DLR) anomaly and the Niño-3.4 index time-series, over the Niño-3.4 region located in the central Pacific. A high anti-correlation was also found over the western Pacific (15–0 S, 105–130 E). There is convincing evidence that the time series of the mean downwelling longwave radiation anomaly in the western Pacific precedes that in the Niño-3.4 region by 3–4 months. Thus, the downwelling longwave radiation anomaly is a complementary index to the SST anomaly for the study of ENSO events and can be used to asses whether or not El Niño or La Niña conditions prevail. Over the Niño-3.4 region, the mean DLR anomaly values range from +20 Wm^−2 during El Niño episodes to –20 Wm^−2 during La Niña events, while over the western Pacific (15–0 S, 105–130 E) these values range from –15 Wm^−2 to +10 Wm^−2, respectively. 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