Abstract
The so-called El Niño-southern oscillation (ENSO) is the most important and influential climate phenomenon of contemporary climate variability, in which oceanic wave dynamics plays an important role. Here we develop and apply an approach based on network theory to quantify the characteristics of El-Niño related oceanic waves using the satellite dataset. We associate the majority of dominant long distance (≥500 km) links of the network with several kinds of oceanic waves, i.e. equatorial Kelvin, Rossby, and tropical instability waves. Notably, we find that the location of the out-going () and in-coming hubs () of the climate network coincide with the locations of the wave initiation and dissipation, respectively. We also find that this dissipation at is much weaker during El-Niño times. Moreover, the hubs of the equatorial network agree with the locations of westerly wind burst activity and high wind vorticity, two mechanisms that were associated with Rossby waves activity. This novel quantification method that is directly based on observational data leads to a better understanding of the oceanic wave dynamics, and it can also improve our understanding of El-Niño dynamics or its prediction.
Highlights
The El Niño-southern oscillation (ENSO) is the largest climatic cycle on annual time scales, and is one of the most important processes that affect the natural climate variability
By transforming the daily and relatively long (∼20 years) satellite based altimeter (i.e., sea surface height (SSH)) records into climate networks using cross correlation, we find that the time delays, the velocities and the directions associated with climate network links can be attributed to equatorial Kelvin, Rossby and tropical instability waves (TIWs)
We construct and analyze the climate network of the tropical Pacific ocean based on daily satellite SSH data
Summary
The El Niño-southern oscillation (ENSO) is the largest climatic cycle on annual time scales, and is one of the most important processes that affect the natural climate variability. The most important El-Niño waves are the equatorial Kelvin waves and long equatorial Rossby waves, that travel at the upper ocean (tens of meters below the surface at the eastern Pacific to a few hundreds of meters at the western Pacific). Long equatorial Rossby waves travel to the west, crossing the Pacific basin in about 7 months. At the same time downwelling long Rossby waves slowly propagate to the west, ‘collide’ with the western boundary of the Pacific ocean, and reflected back as upwelling Kelvin waves. These reflected Kelvin waves cool the eastern Pacific ocean—when they reach the eastern Pacific after about ten months they terminate the El-Niño
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