Comparison of NINO1+2 and NINO3.4 indices in terms of ENSO effects over the Euro-Mediterranean Region

El Nino Southern Oscillation (ENSO) is a phenomenon in the equatorial Pacific that could have profound effects on climate around the world. Although ENSO impacts are fairly well-defined for south and north America, Australia and south-eastern Asia, they are not very clear for Euro-Mediterranean region. Some studies indicate that the negative phase of ENSO in Nino3 and Nino3.4 indices have similar effects in the negative phase of North Atlantic Oscillation (NAO).  ENSO impacts and teleconnection patterns are mostly studied using the Nino3.4 index. However, some recent studies indicate that the Nino1+2 index has higher correlation with climate variability over the Euro-Mediterranean region.

In this study, we investigate impacts of ENSO over the Euro-Mediterranean climate variability and atmospheric dynamics using the Nino1+2 and Nino3.4 indices. Additionally, we also tried to understand if there is any relation between ENSO and the Mediterranean and East Asian troughs. NCEP/NCAR Reanalysis surface air temperature, precipitation and 500 hPa geopotential height datasets and SST-based ENSO indices from ERSSTv4 were used in the analysis for boreal winter (December-January-February) for a period of 1950 - 2019. We utilized the Pearson correlation analysis to reveal the relation between these indices and climate parameters and the composite analysis  to define the pattern differences between the cold and warm phases of the indices.

Our preliminary findings show that there is a distinct correlation pattern between Nino indices and surface air temperature over the region of interest. Nino1+2 index has a more distinct dipole pattern with a significant positive correlation pole over central Europe and negative pole over north-eastern Africa. However, Nino3.4 indicates a rather zonal correlation dipole pattern whose poles are over northwest Africa (strongly positive) and northeast Africa (negative). It is also found that the Mediterranean trough location is sensitive to the phase of ENSO for both indices. Namely, the Mediterranean trough tends to be in the west of its climatological location for La Nina phases of Nino1+2 and Nino3.4, which affects the distribution of surface temperature and precipitation over the Euro-Mediterranean and Middle East and Northern Africa (MENA) regions. We concluded that the La Nina phase of Nino1+2 seems to play a more distinctive role in the dipole pattern. The surface air temperature is colder over the entire Europe while it is opposite in the Middle East region including Turkey. This dipole pattern is also detected for the La Nina phase of Nino3.4, but it is mostly observed over southwestern Europe and northern Africa. Comparison between the La Nina and El Nino phases of the Nino1+2 index indicates that for the La Nina phase precipitation is larger over the Aegean Sea and Italy and smaller in northern Europe.