Sun, May 29, 2022

perspective

Don’t get too used to El Nino


Hidden beyond the current El Nino hype, solid evidence exists that the demise of the record-breaking event has already begun and that all traces of it will have vanished by next August.

The warm sea surface temperature (SST) anomalies in the central-east Pacific Ocean, which characterise El Nino and have been steadily rising since early March, have reached a plateau in recent weeks (http://tmsnrt.rs/1UXHGTv).
The current El Nino event has been compared to those in 1997/98 and 1982/83, the strongest two events observed since 1950. Last month, SST anomalies surpassed the record-warm monthly values of November 1997.
The 1997/98 and 1982/83 El Nino events began dismantling in almost the exact same way, both during the height of their strength, and the data shows an uncannily similar pattern is already unfolding in 2015.
This certainly marks the beginning of the end for the monster El Nino, and not only are models in agreement that the phenomenon has already reached its peak, several of them strongly indicate that the scenario will be vastly different one year from now. And the historical data backs that theory near-perfectly.
 
Death of a giant
Several atmospheric and oceanic ingredients work together to support El Nino, but the phenomenon appears virtually unsustainable without two key variables: trade winds in the western equatorial Pacific Ocean and temperature anomalies below the ocean’s surface.
While El Nino is directly defined by activity in the central and eastern Pacific, it cannot be long-lived without support from the entire ocean.
Strongly reversed trade winds in the western basin sustain El Nino by continuing to push anomalous warm pools of water eastward into the Nino region.
But once an ingredient is lost – either the western Pacific trades revert to their normal easterly direction or the ocean waters cool down – the process is disrupted and El Nino’s lifeline is essentially severed.
In both 1982 and 1997, western trade winds were highly reversed but abruptly returned to normal within one month at the end of both years. Although these winds have not been as anomalously strong in 2015, the same rapid jump occurred last month (http://tmsnrt.rs/1J2iEB1).
One month later in both January 1983 and 1998, temperature anomalies in the upper 300 meters of the equatorial Pacific Ocean took a nose dive and did not return to levels warmer than normal until two years later (http://tmsnrt.rs/1J2jgXc).
The subsurface Pacific waters are still quite warm at present, similar to “pre-crash” levels in 1982 and 1997, but there are already signs that they could soon take a tumble.
SST anomalies across the equatorial Pacific basin have cooled roughly one-half a degree over the last four weeks. At the same time, a large pool of cold water beneath the surface in the western Pacific has been expanding eastward, nearly doubling in size over the past two months.
By July in both 1983 and 1998, SST anomalies in the equatorial Pacific were back near zero or even in negative territory. If the current El Nino in fact meets its demise in the exact fashion as its predecessors, it too will likely be gone by mid-2016.
Current climate models only predict through early autumn 2016, but they have already been indicating a rapid descent from El Nino over the next few months, and historical data suggests the same.
A simple inspection of the years immediately following past strong El Ni??o years reveals that the chances are very likely for La Nina, classified by cool SST anomalies in the equatorial Pacific, to be present by the close of 2016.
Since 1950, the four strongest El Nino events led to the strongest, seventh-, and eighth-strongest La Nina events on record in the following year. Weak La Nina conditions were observed in the fourth instance.
Consensus among international climate models is that by August, SST anomalies will be near zero, and are likely to keep declining toward the end of 2016 (http://tmsnrt.rs/1UXILL0).
But in the near term, El Nino will continue to have a big presence. Although models indicate that El Nino likely reachedi ts peak last month, the globe can still expect to be in an El Nino state through the first half of 2016.
Both the rapid descent into La Nina and the event itself have presented problems for North and South America in the past.
The transition period has been associated with several summer droughts in the United States, and key corn and soybean-growing areas of Argentina and Southern Brazil tend to be drier than normal during La Nina events.
Additionally, the Northern United States has more frequently observed brutally cold and snowy winters during La Nina events than El Nino ones.

Published : December 25, 2015

By : Karen Braun Reuters