Analysis of pre-El Niño and La Niña events using climate network approach

El Niño Southern Oscillation is a climate mode in which sea surface temperature anomalies are warmer (cooler) in the central-eastern (western) Pacific during an El Niño (La Niña) phase. It is one of the most important climatic phenomena and has a substantial influence on global climate patterns due to its ability to change the global atmospheric circulation induced by ocean–air coupling. We analyze the space-embedded climate networks’ connectivity pattern to study the preconditions of El Niño and La Niña phases. We observe that during the March–April–May period, the spatially embedded climate network connectivity pattern exhibits the alteration of atmospheric warming activity preceding El Niño and La Niña phases. These distinct preconditions of both phases are observed during the spring season prior to the event’s onset. We study the distribution of teleconnection along with the pattern of connectivity of climate networks to understand the change in the connection topology. Before El Niño events, we observe the dominance of only the neighboring links, and preceding the La Niña events, a higher number of neighboring and long-range links appeared in the networks during March–April–May, simultaneously with the Tropical/ Northern hemisphere warming up. Finally, we observe that before La Niña events, the climate network is densely connected.