Bob - when I worked at the Bureau of Meterology (before 1989) we used Southern Oscillation with El Nino.

The BOM website shows Southern Oscilation Index linked with El Nno.

I assume the media took up El Nino as it is a more colourful term

by-the-by, I remember them getting hold of Wind Chill Factor - now that was flavour of the month for a while!!

sandra