The ‘triple dip’ La Niña


One of the longest La Nia episodes in recorded history, the current La Nia phase of the equatorial Pacific Ocean is expected to last for at least another six months. Additionally, it is only the third episode since 1950 to continue for a third year in a row.

On August 31, the World Meteorological Organization (WMO) predicted that La Nina will become a "triple dip" La Nina for the first time in this century if it persisted into three successive winters in the northern hemisphere.

In the upcoming months, this is anticipated to have wide-ranging effects on weather events around the world and may make different regions' floods and droughts worse.

ENSO (El Nino and Southern Oscillation)

The current La Nia phase of the equatorial Pacific Ocean is anticipated to endure for at least another six months, making it one of the longest La Nia occurrences in recorded history. It is also only the third episode to run for a third consecutive year since 1950.

On August 31, the World Meteorological Organization (WMO) stated that if La Nina extended through three straight winters in the northern hemisphere, it would become a "triple dip" La Nina for the first time in this century.

This is projected to have significant implications on global weather events in the following months and could exacerbate floods and droughts in various locations.

Only El Nino = [Warm water in Eastern Pacific + Cold water in Western Pacific].

Only SO = [Low Pressure over Eastern Pacific + High Pressure over Western Pacific]

ENSO = [Warm water in Eastern Pacific + Low Pressure over Eastern Pacific] + [Cold water in Western Pacific + High Pressure over Western Pacific].

In ENSO formation of an El Niño [Circulation of Water] is linked with Pacific Ocean circulation pattern known as the southern oscillation [circulation of atmospheric pressure]

Despite the fact that ENSO is a single climate phenomenon, it has three possible states or phases:

above-average sea surface temperatures (SST) in the central and eastern tropical Pacific Ocean, or warming of the ocean's surface.

Because of this buildup of warm water, the thermocline in the eastern Pacific Ocean recedes, preventing the upwelling of cold deep ocean water near the Peruvian coast. Industry of fishing is impacted

It is related to India's monsoon season having less rainfall than usual.

SSTs that are below average or the ocean surface cooling in the central and eastern tropical Pacific Ocean.

It is linked to a relatively more favourable monsoon season in India.

Neither El Nino nor La Nina

Tropical Pacific SSTs frequently fall just below average.

El Nio and La Nia episodes often begin in the months of March and June and run for nine months to a year.

Prior to waning or disappearing by March or April of the following year, they are at their peak throughout the winter (November to January in the northern hemisphere).

The occurrences of El Nio and La Nia, however, are not identical. They vary in length and power.

El Nio episodes are more common and are typically accompanied by more severe weather conditions. A La Nia, on the other hand, has a longer run and is more likely to last more than one year. Because of this, multi-year La Nia events—those lasting more than 12 months—are more frequent.

About ‘Triple dip’ La Niña

These El Nino and La Nina episodes can occasionally last for substantially longer lengths of time.

The El Nino of 2015–16, which lasted for 19 months and was one of the longest ever recorded, earned the nickname "Godzilla" for its continued high intensity.

The triple dip When the La Nina period lasts for three or more consecutive winters, the equatorial Pacific Ocean's surface temperature decreases over an extended period of time.

For instance, the present La Nino episode, which has been dubbed a "triple dip" La Nino, began in September 2020, has persisted for the past 24 months, and appears likely to continue for another six months.

Six of of the thirteen La Nino episodes since 1950 have lasted two years (double dip La Nina), and three of them, including the present one, have lasted three years.

When compared to El Nino: In comparison, 15 out of 20 El Nino incidents (or over 75 percent) came to an end within a year. There has never been a third year of an El Nino.

Even though extended La Nia occurrences are typical, the current one differs significantly from the prior two triple-year events in one key area.

Strong El Nino episodes preceded both of the earlier occurrences, one between 1973 and 1976 and the other between 1998 and 2001, and prolonged La Nina events were caused by longer heat dissipation times as a result of more heat being collected in the oceans.

The cause of the present La Nino event is not entirely obvious at this time because there hasn't been a powerful El Nina to precede it.

Evaluating the likely impact on India

During the monsoon season, La Nia is linked to abundant rainfall. El Nio, which is known to reduce monsoon rainfall, is the opposite of this.

So, if La Nia persists, we may be able to anticipate another year of good or typical monsoon rainfall.

India has received 740.3 mm of rain so far this year, which is 7% more than the seasonal normal through August 30.

Although influential, the ENSO state does not solely determine the amount of rain that India receives during the monsoon season, and there is no direct relationship between the two.

Additionally, ENSO has macro-level effects. At the local level, rainfall varies greatly, and these differences are getting worse due to climate change.

Impact on other regions

La Nia, for instance, is linked to extremely dry winters in most of the United States. La Nina has also contributed to the recent widespread drought in the United States.

The United States' National Oceanic and Atmospheric Administration (NOAA) just announced August 2022 to be the sixth-hottest August in the previous 143 years.

La Nia is anticipated to increase rainfall in Australia, Indonesia, and the rest of the tropical region. For instance, this year's flooding in eastern Australia.

La Nia can also be partially blamed for the excessive rainfall in Pakistan, which is currently experiencing its greatest flooding crisis.

According to the World Meteorological Organization (WMO), the continuation of La Nia will probably cause the drought in Africa to get worse.

The scientists also predict that the world will experience an excessively active Atlantic Hurricane season in 2022 as a result of this triple dip.

Climate change link

The natural variability of ENSO is not well known because there are no ancient records. Additionally, no solid evidence linking ENSO episodes to global warming has been found.

Uncertain natural variability is brought on by the irregular occurrences of El Nio or La Nia, which can appear every two years or even seven years at times. Consequently, it is challenging to estimate the impact of global warming.

There isn't any concrete evidence, but a small number of specialists think that climate change is causing El Nio and La Nia occurrences to occur more frequently and intensely.

This is due to the fact that trade winds are equally crucial in causing ENSO episodes, and variations in their strength are difficult to attribute to global warming.

Another type of connection between global warming and ENSO episodes is supported by the following evidence:

The colder ocean surfaces help the oceans to absorb more heat from the atmosphere during La Nia years. As a result, the air temperatures often decrease, creating a cooling effect.

However, according to the WMO, while La Nia's cooling effect is temporarily delaying the increase in global temperatures, the long-term warming trend will continue to increase.

In addition, it was reported that worldwide average temperatures were around 0.9 degrees Celsius higher than the norm for the 20th century.

Source: The Indian Express

Posted by V.P.Nimbalkar on 21st Sep 2022