Abstract
Abstract. 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 off-equatorial western Pacific region 7–15° N 150–170° E, precedes the Niño-3.4 index time-series by about 7 months and the pattern of this anomaly is indicative of ENSO operating through the mechanism of the western Pacific oscillator. 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.
Highlights
The El Nino Southern Oscillation (ENSO) is the dominant natural interannual climate fluctuation on Earth and involves the interaction between the tropical Pacific Ocean and the overlying atmosphere
For the more extended off-equatorial region that is regions causes the downward shortwave radiation (DSR) decrease, which together with the centred in the northern hemisphere we show the time series rise of the ocean thermocline via Ekman pumping, results of DSR anomaly
Our model calculations, which are based on ISCCP-D2 cloud climatologies, temperature and humidity profile information from NCEP/NCAR reanalysis and aerosol data from GADS, show a high variability in the downward shortwave radiation (DSR) at the surface of the Earth over the tropical and subtropical Pacific Ocean during ENSO events
Summary
The El Nino Southern Oscillation (ENSO) is the dominant natural interannual climate fluctuation on Earth and involves the interaction between the tropical Pacific Ocean and the overlying atmosphere. The Earth’s climate system is driven by the radiative energy balance between the solar shortwave radiation (SW) absorbed by the atmosphere and the surface of the Earth and the thermal longwave radiation (LW) emitted by the Earth to space In this respect, ENSO events are expected to be associated with the spatial and temporal variability of the radiative energy balance at the surface over the tropical and subtropical Pacific ocean. The variability of DSR, the component of the net heat into the ocean with the largest magnitude, reflects mostly fluctuations in cloud cover caused by variations in atmospheric circulation and it is very important in order to describe and study the intensity or duration of ENSO events. Downward shortwave radiation at surface Mean DSR when El Nino, La Nina, or neutral conditions prevail, respectively El Nino DSR anomaly with respect to the mean DSR for the La Nina years equal to DSREN-DSRLN El Nino or La Nina DSR anomaly with respect to the mean DSR for the neutral years equal to DSREN-DSRNE or DSRLN -DSRNE DSR anomaly with respect to all years DSR
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