>" Are central El Ninos as periodic as eastern ones?"

The eastern El Nino is considered the "canonical" El Nino. As you say it may be that the central (Modoki?) is an overlapping or modifying effect.

Here is a paper that at least shows the components:
[1]F. Xie, J. Li, W. Tian, J. Zhang, and C. Sun, “The relative impacts of El Niño Modoki, canonical El Niño, and QBO on tropical ozone changes since the 1980s,” Environmental Research Letters, vol. 9, no. 6, p. 064020, May 2014. http://iopscience.iop.org/1748-9326/9/6/064020/pdf/1748-9326_9_6_064020.pdf

Parse this sentence:
> "Modoki activity can affects the tropical TCO is likely to cause by directly transports ozone-poor air in the tropics from the
troposphere to the stratosphere, which leads to significant ozone decreases in the lower-middle stratosphere (figures 3
and 4), since El Niño Modoki can significantly enhance the BD circulation (figure 5). "

These narratives are so obtuse.