CAFE Project

Climate Components: Science Update

Figure 1: Global precipitation anomalies during the boreal winter of the 1997-1998 El-Niño event, as represented by NCEP/CMAP2 observations (top), the GISS 2x2.5 resolution AGCM (middle), and the GISS 4x5 AGCM (bottom). (Click for larger image)

Figure 2: Global precipitation anomalies during the boreal winter of the 1998-1999 La-Niña event, as represented by NCEP/CMAP2 observations (top), the GISS 2x2.5 resolution AGCM (middle), and the GISS 4x5 AGCM (bottom). (Click for larger image)

Global Results

High resolution and low resolution versions of the GISS global atmospheric general circulation model, forced with monthly observed SST's, are able to capture the prominent features of the anomalous ENSO circulation. In Fig. 1, we see excess rainfall over the east Pacific accompanied by drier than normal conditions over the Maritime Continent during an El-Niño event, whereas in Fig. 2, La-Niña conditions yield opposite patterns. The magnitude of the rainfall anomalies appears to be too small in the models, and most notably in the high resolution case. The models also appear to capture some of the more subtle teleconnection patterns associated with the ENSO cycle, such as wetter (drier) than normal conditions over parts of the southern U.S. during warm (cold) events.

Figure 3: South American precipitation anomalies during austral fall of the 1999 La-Niña event, as represented by NCEP/CMAP2 observations (top), the GISS 2x2.5 resolution AGCM (middle), and the GISS 4x5 AGCM (bottom). (Click for larger image)

Figure 4: South American surface temperature anomalies during austral summer of the 1997/1998 El-Niño event, as represented by NCEP/CMAP2 observations (top), the GISS 2x2.5 resolution AGCM (middle), and the GISS 4x5 AGCM (bottom). (Click for larger image)

Results for South America

Both models are able to capture the excess moisture associated with La Niña (see Fig. 3) over northern and northeastern Brazil, although the 2x2.5 runs appear too dry along the Atlantic Coast and too wet over the eastern Amazonian basin. Over Uruguay, by contrast, the 2x2.5 model (middle) does a particularly good job of simulating the anomalous dry conditions historically associated with La-Niña and evident in the 1999 observational data (top).

Both models, which are forced by monthly observed SSTs, are able to capture the trademark warming off the Peruvian coast during El-Niño events (see Fig. 4). Both models also reproduce warmer than normal conditions throughout the subtropics, although the high resolution model (middle) performs better (relative to the observational data [top]) over northeast Brazil. On the other hand, the low resolution model better simulates the anomalous cooling in the mid-latitudes.

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