La Nina: Girl on the rampage

B. Khan in Dawn (Pakistan): Australia, Brazil and Sri Lanka are still reeling from the devastating effect of La Nina and it comes as an extremely bad news indeed that they, along with South Africa, will receive more heavy rainfall over the coming weeks, possibly even months if some climate experts are correct.

La Nina, Spanish for ‘Little girl’, is the ‘cool’ phase of the slighter better known El Nino or ‘The boy’ which represents the ‘Southern Oscillation’ in its ‘warm’ phase. The combined effects of the two are generally referred to as Enso and this is, broadly speaking, a periodic climate pattern previously known to occur in the tropical eastern Pacific Ocean zone every five years or so with El Nino generally being of longer duration than his little sister.

The arrival of an El Nino event is announced by the ocean surface warming in this particular area by at least 0.5C above average and La Nina by a reduction of a similar degree. This, along with alterations in surface pressure over Australia, Indonesia and the Indian Ocean and corresponding changes in the ‘trade winds’ serve as an early warning system that one or the other face of Enso is about to make an impact. Each separate event can last from nine months to two years and, until as recently as 20 years ago, was relatively easy to predict but all this changed in 1986 when a completely new phenomenon arose.

The traditional Enso, centred on ocean surface temperature anomalies in the eastern Pacific Ocean could very well have been pushed aside by what has been christened El Nino ‘Modoki’, this word meaning ‘different’ in Japanese, which arises in the central rather than the eastern Pacific and which has some new ingredients including the formation of an increased number of Atlantic Ocean hurricanes.

This new version, the Central Pacific El Nino/La Nina, has occurred six times since first being observed in 1986 with the strongest one running from 2009-10 in its El Nino phase and from around June 2010 until either the summer of 2011 or the early months of 2012 depending on which climatologist is correct, in the shape of La Nina.

It is this La Nina being experienced right now which is causing cooler ocean surface temperatures in the Pacific and strengthening trade winds thus causing heavier precipitation in Australia, Sri Lanka and Brazil….

The La Nina state of ENSO, from NOAA