Is there an El Nino coming?
The controlling wind flow in both hemispheres is that of the Trade Winds which feed the Torrid Zone and its core rainfall belt (the Inter-Tropical Convergence Zone: ITCZ) with a regular, reliable moist air inflow. This Torrid Zone matches its latitude range with the Solstice, north and south, to describe our seasons. This sets up an imbalance which intermittently adjusts itself: Nature at work! This adjustment is described as an oscillation, a negative departure, from the normal. The term El Nino (sea-surface temperature initially) coupled with the Oscillation is applied and weather patterns, world-wide, have been matched to this El Nino/Southern Oscillation.
This is where we come in.
Across our climate record, these oscillatory effects dictate influences on our Arid Climate.
We have proven increases in temperature and a warming aspect is evident in the climate. At home, we have witnessed a southward advance of the Torrid Zone, advecting tropical Congo air into our northern skies. The resultant rains brought an unusual level of consistency. Further afield, the oscillation identity during the past 20 and more calendar years switches from the negative to the positive while retaining the positive airflow pattern (La Nina) throughout. The positive oscillation is identified by a north to south flow rather than a zonal flow which is west to east, zonal, A moister advection range is present rather than a drier limit to a moist inflow.
It does appear that the various weather models may not have a full grasp of this subtle departure. The oscillatory identity is based on data from Darwin and Tahiti: both are sufficiently close to the Torrid Zone, so this annual extension has embraced them accordingly. Surface and lower level ranges of synoptics respond to this extension with a persistent repositioning of high pressure cores some 10o further south. The overall evidence is that the La Nina has collapsed, despite the Pacific Ocean convergence zone indicating a negative oscillation.
In spite of the parameters associated with a positive range persisting the likely results are out of step. High Pressure cores (frequently stronger than 1030hPa) enable steady outflows of the Trades to maintain cooler air advection toward the ITCZ. Observations are noting inconsistency where sea temperatures are concerned.
But the urgency, because of recorded effects not only on our day-to-day weather but also on derogatory effects across a season, demands attention.
From our angle, it is difficult to see a reversal of the trends of the past decade and more. There was one disappointing rainfall season/year overall (2007) when the moist aid advection was restricted but otherwise, by our standards wetter prospects prevailed for most of the past nine years.
Currently, outlooks remain limited to neutral with an open eye toward a negative inclination. Do we rely on a rainfall year pattern like 2010 to recur? It is difficult to deny because our unique geography may well exert its more rainfall favourable bias. It does imply that existing knowledge of previous oscillatory events maybe outdated or at least distorted from the less favourable stance.