During the last 4 weeks, above average sea surface temperatures (SST’s) have strengthened across much of the central and eastern equatorial Pacific Ocean. Sub surface temperature anomalies have been positive since March 2023, albeit with fluctuating scales. However, from October 2023 onward, positive anomalies have increased constantly and breached 1.5°C mark. The consistent rise in sea temperature on account of El Nino warming seems to be increasing the sea level. While the Antarctica ice content is the lowest on record, the sea level is noticeably quite high.
A group of Oceanographers at the French National Centre for Scientific Research ( CNRS) has found evidence that suggests an unexpected sea level rise over the years 2014 to 2016 was likely due to consecutive El Nino events. World oceans are expected to have a rise in sea level approximately 4mm a year, on account of continued ice melting. But, over 2 years period of 2014-2016, ocean levels rose at approximately double the expected rate. After the event, the ocean levels went back to the previously estimated rate. Such events led to less rainfall on the Amazon basin and more on the Pacific Ocean and large parts of Argentina. Most of it ran off to the ocean.
ENSO: El Nino and Southern Oscillation Indices (SOI) remain consistent with ENSO conditions. Peak values of the Oceanic Nino Index (ONI) hover around 2°C. The three-month running mean of SST anomalies in the Nino 3.4 region has shot up from 0.5°C in the quarter Apr-May-Jun to 1.8°C in the quarter Sep-Oct-Nov.
The monthly average of SOI has now risen to 0.8 in Nov 2023, as against the earlier mean of 0.5 in Oct 2023. Therefore, the SO remains in close support of El Nino, as is normally seen during a fully blown El Nino episode. ENSO neutral is likely but not before May 2024.
IOD: The positive Indian Ocean Dipole event continues. However, the index values appear to have eased out from their earlier peak value of Oct 2023. These are unlikely to strengthen again. On the contrary, further drop is imminent, as the monsoon trough shifts to Southern Hemisphere. It may plunge to less than 1°C by month end. The weekly index value of IOD for the week ending 03 Dec 2023 was 1.20°C. The highest value of IOD during the current episode was 1.92°C on 16 Oct 2023. It also means that the IOD event has likely past its peak.
MJO: A fairly strong pulse of Madden-Julian Oscillation is currently placed over the Maritime Continent in Phase 4 & 5. It is expected to move into Western Pacific in Phase 6 & 7, for the next about 10 days. Subsequently, the amplitude is likely to shrink while the pulse transits to Western Hemisphere and Africa in Phase 8. Model consensus places the MJO in Phase 6 during the week 11-17 Dec 2023. This will possibly suppress the convection over the Indian Ocean. There is no likelihood of another storm spinning up in the Indian Seas till 3rd week of December. As such, the frequency of storms decrease significantly in the 2nd half of December.
El Nino shifts rainfall from land to ocean, raising sea level. Its opposing phase, La Nina, shifts rainfall to land restricting this rise. However, it needs corroboration with quantitative analysis based on long period data.