El Nino / La Nina is a global phenomenon and a lot of international agencies closely follow its development and progress. Climate Prediction Center (CPC) is one such agency which monitors El Nino right from its initial indications to its end and issue the relevant advisories. Final El Nino Advisory is issued when El Nino or La Nina conditions have ended. La Nina ‘Watch’ means, conditions are favorable for development of La Nina with a notice period of six months.
The El Nino / La Nina phenomenon is the biggest cause of year to year difference in weather in many regions. In La Nina years, the east to west Pacific trade winds are stronger, pushing warm surface water to the west and drawing up deeper cooler water in the east. El Nino/ La Nina events tend to develop during the period May-June and reach their peak during fall of the year or Northern Hemispheric winters.
Their respective heating and cooling effect takes weeks to be felt. Water is known to have long memory and therefore retains, both ‘heat’ and ‘cool’ for longer duration than any other substance on this planet earth. Under climate change, the impact of El Nino/ La Nina events are going to get stronger and one has to super impose this effect on the ever growing threat of climate change itself. These two things, put together will possibly lead to unprecedented climate chaos and increase in the extreme weather events In different parts of the globe.
ENSO: In the last four weeks, equatorial SST’s were above average in the central and western Pacific. Near to below average SST’s sustained in the east-central and eastern Pacific Ocean. However, the average SST’s have weakened across the equatorial Pacific Ocean. Also, the negative sub-surface temperature anomalies have dominated the equatorial Pacific Ocean.
The oceanic and atmospheric conditions across the tropical Pacific indicate the continued decline of the El Nino event. However, the Nino indices across the region are hardly showing any further dilution. Rather, Nino 4 and Nino 1+2, on either flank have warmed slightly. Nino 3.4 index, the representative of ONI is refusing to go sub-zero to facilitate start of La Nina. The 30 day Southern Oscillation Index stands within the neutral-ENSO range and the average value for the month of May was 0.5.
IOD : The IOD is one of the dominant mode of variability of the tropical Indian Ocean. It is recognized as having important telecommunication worldwide, but its influence on the Indian Summer Monsoon and relationship with ENSO is considered powerful. The positive mode of IOD has an evidence of moisture transport over the western Indian Ocean. Considering major ENSO and IOD events, it has been acknowledged as to how in 1997, the failure of negative relationship between ENSO and the ISMR was associated with a positive IOD event developing that summer.
Strong IOD of 1994 has been responsible for a stronger than normal monsoon (112.5% of LPA). Recently, a big IOD event recorded in 2019 proved its efficacy by saving the monsoon and demonstrated the complex relationship between ISMR, IOD and ENSO. Possibly, the internal dynamical processes get influenced and remain far from being understood, thoroughly.
The IOD is currently neutral. From the past records, the index is known to have gradual rise or fall and is least known for steep variations. The index is tantalizing and hovering around zero-zero for the last two weeks. The latest value of IOD for the week ending 09thJune 2024 was -0.02°C. It mandatorily has to cross the threshold of +0.4°C to complement monsoon rainfall.
MJO: The Madden-Julian Oscillation is likely to meander over Western Pacific and Western Hemisphere, in Phase 7 & 8. The amplitude continue to be small and restricted to the unit circle. Such stance of MJO will continue to promote drier conditions across the Indian Ocean basin. Bay of Bengal and Arabian Sea is unlikely to get support from MJO for emergence of any monsoon system.
ENSO-neutral is likely anytime soon. But, La Nina will build up only half way through the monsoon. Also, there is always a lag between its build up and influence on the monsoon activity. IOD, as such is keeping the monsoon on tenterhooks. Being just neutral will not suffice to unleash the monsoon rains. Both these parameters need to get aligned at the earliest and work in tandem to pull out victory for the monsoon 2024.
