Comparative Evaluation of Niño1+2 and Niño3.4 Indices in Terms of ENSO Effects Over the Euro-Mediterranean Region

Global or regional impacts of El Ni & ntilde;o Southern Oscillation (ENSO) have predominantly been investigated through the Ni & ntilde;o3.4 index, representing the sea surface temperature (SST) variations in the central Tropical Pacific. In this study, we comparatively evaluated the usefulness of Ni & ntilde;o1+2, a relatively less utilised index that represents SST variability in the Eastern Tropical Pacific. In our analyses, we focused on ENSO impacts on Euro-Mediterranean (EM) climate variability during boreal winter, using data from the NCEP/NCAR Reanalysis. The correlation analysis involving Ni & ntilde;o1+2 depicts more distinct temperature and precipitation patterns over the EM region. Amongst the SST-based Ni & ntilde;o indices, it has the highest correlation with the East Atlantic index (0.47, statistically significant at > 99% confidence level), a prominent regional teleconnection associated primarily with the strength of the East Atlantic ridge, which produces dipole-type climate patterns between East Atlantic/Western Europe and Central/Eastern Mediterranean. Moreover, its lagged correlations with the following spring (0.39), summer (0.31), and autumn (0.36) are all statistically significant at >= 99% confidence levels. The composite analysis shows that different Ni & ntilde;o regions have distinct effects on atmospheric circulation and climate in the EM region. The Ni & ntilde;o1+2 index is particularly helpful in identifying the years when warm SST anomalies of El Ni & ntilde;o extend to the Eastern Equatorial Pacific, which results in a reversal of temperatures across the EM region. Thus, this study suggests that Ni & ntilde;o1+2 is a useful index for studying climate variability and predictability in the EM region, especially when used in conjunction with other Ni & ntilde;o indices, as it captures some ENSO features that they may not encompass.