EI Niño/La Niña Status
Updated on 6 September 2022
The El Niño Southern Oscillation (ENSO) monitoring system state is “La Niña Conditions”. Cool Nino3.4 sea surface temperatures and sub-surface temperatures indicate La Niña conditions. Atmospheric indicators (OLR1 and wind anomalies) over the tropical Pacific Ocean remain consistent with La Niña conditions. The Nino3.4 index was -0.85°C for July 2022 and 1.01°C for the May – July 2022 three-month average.
Models predict the La Niña conditions to continue for the September to November period. However, the chance of La Niña conditions decreases towards the end of the year, with ENSO neutral conditions more likely to be present by the beginning of next year.
The Indian Ocean Dipole is in its negative phase. Models predict the negative IOD to remain for the next three months.
1 OLR: Outgoing Longwave Radiation
Further Information on ENSO
ENSO conditions are monitored by analysing Pacific sea surface temperatures (SSTs), low level winds, cloudiness (using outgoing longwave radiation), and sub-surface temperatures. Special attention is given to SSTs, as they are one of the key indicators used to monitor ENSO. Here, three different datasets are used: HadISST, ERSSTv5, and COBE datasets. As globally, SSTs have gradually warmed over the last century under the influence of climate change, the SST values over the Nino3.4 will increasingly be magnified with time, and hence appear warmer than they should be. Therefore, this background trend is removed from the SST datasets (Turkington, Timbal, & Rahmat, 2018), before calculating SST anomalies using the climatology period 1976-2014. So far, there has been no noticeable background trend in the low-level winds or cloudiness.
El Niño (La Niña) conditions are associated with warmer (colder) SSTs in the central and eastern Pacific. The threshold for an El Niño (La Niña) in the Nino3.4 region is above 0.65°C (below -0.65°C). El Niño (La Niña) conditions also correspond to an increase (decrease) in cloudiness around or to the east of the international dateline (180°), with a decrease (increase) in cloudiness in the west. There is also a decrease (increase) in the trade winds in the eastern Pacific. Sub-surface temperatures in the eastern Pacific should also be warmer (colder) than average, to sustain the El Niño (La Niña) conditions.
For ENSO outlooks, information from the World Meteorological Organization (WMO) and international climate centres are assessed. The centres include the Climate Prediction Center (CPC) USA, the Bureau of Meteorology (BoM) Australia, as well as information from the International Research Institute for Climate and Society (IRI) which consolidates model outputs from other centres around the world. Each centre uses different criteria, including different SST thresholds. Therefore, variations between centres on the current ENSO state should be expected, especially when conditions are borderline.
The sea surface temperatures (SSTs) over the central and eastern tropical Pacific overall represented La Niña conditions in July 2022 (Figure 1). However, the SST anomalies in the Nino3.4 Region (red box, Figure 2) were not as strong as in recent months. A negative Indian Ocean dipole is also visible in Figure 2, with cooler than average SSTs in the western Indian Ocean and warmer than average SSTs in the eastern Indian Ocean. Most models predict the La Niña conditions and the negative Indian Ocean Dipole to persist for the next three months.
Figure 1: Detrended SST anomalies for July 2022 with respect to 1976-2014 climatology using ERSST v5 data. Red (blue) shades show regions of relative warming (cooling). The tropical Pacific Ocean Nino3.4 Region is outlined in red. The Indian Ocean Dipole index is the difference between average SST anomalies over the western Indian Ocean (black solid box) and the eastern Indian Ocean (black dotted box).
Looking at the Nino3.4 index in Figure 2, until April 2021, the Nino3.4 index was within the La Niña range. Between May and July 2021, the index was cooler than average, but within the neutral range, becoming borderline between La Niña and neutral conditions in August 2021. From September 2021 onwards, the 1-month Nino3.4 index was again within the La Niña range, although there was a weakening of the index in June and July. La Niña conditions are considered present when the 1-month cold SST anomalies (observed or forecast) persist or are predicted to persist for at least four months below the threshold, along with supporting atmospheric observations.
Figure 2: The Nino3.4 index using the 1-month SST anomalies. Warm anomalies (≥ +0.65; brown) correspond to El Niño conditions while cold anomalies (≤ -0.65; blue) correspond to La Niña conditions; otherwise neutral (> -0.65 and < +0.65; grey).
Model outlooks from Copernicus C3S (Figure 3), based on the Nino3.4 SST index, show that most models predict the La Niña conditions to persist until the end of the year, although ENSO neutral conditions becoming increasingly likely by January 2023. A few models predict a strengthening of the La Nina conditions in October and November, however, most models predict the La Nina conditions to be weak or moderate during the September to November period.
Figure 3: Forecasts of Nino3.4 index’s strength until January 2023 from various seasonal prediction models of international climate centres (image credit: Copernicus C3S).
Historical ENSO Variability
To classify a historical El Niño event, the 3-month average Nino3.4 value must be above 0.65°C for 5 or more consecutive months. For La Niña events, the threshold is -0.65°C. Otherwise it is considered neutral. ENSO events with a peak value above 1.5°C (El Niño) or below -1.5°C (La Niña) are considered strong. Otherwise, the events are considered weak to moderate in strength. The following figure (Figure 4) shows the development of the Nino3.4 index for the most recent El Niño and La Niña events in comparison to other El Niño/La Niña events.
Figure 4: Three-month Nino3.4 index development and retreat of different El Niño (left)/La Niña (right) events since the 1960s. The most recent El Niño and La Niña events are in red and purple, respectively.
Impact of El Niño/La Niña on Singapore
During the Southwest Monsoon months from June to September, as well as October, the correlation of ENSO with rainfall over Singapore is strong (Figure 5), i.e. if an ENSO event is present, the rainfall patterns are likely to be influenced by a moderate or strong event. When there is no ENSO event, there is a large variability in rainfall patterns across the neutral ENSO state during this period (Figure 6).
Figure 5: Correlation between total seasonal rainfall (averaged over 5 Singapore stations) and seasonal Nino3.4 index from 1961-2017 centred on the month indicated (e.g. for June’s value it corresponds to season May-June-July). The statistically significant correlations at the 95% level are underlined, at 99% level in red.
Figure 6: Singapore rainfall anomalies for June – October (as a percentage of departure from long-term rainfall average) arranged in the order from strong La Niña (left) to strong El Niño (right). Brown bars denote El Niño years’ anomalies, blue bars denote La Niña years’ anomalies, and grey bars denote ENSO neutral years’ anomalies.
References
Turkington, T., Timbal, B., & Rahmat, R. (2018). The impact of global warming on sea surface temperature based El Nino Southern Oscillation monitoring indices. International Journal of Climatology, 39(2).