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Authors: 超级管理员 | Edit: tianfuyou
5.3 Update on El Niño
According to the Australian Bureau of Meteorology, predictions for the El Niño–Southern Oscillation (ENSO) are at El Niño ALERT status. Sea surface temperatures (SSTs) in the tropical Pacific have exceeded the threshold for an El Niño event and climate models suggest this is likely to persist at least until the end of this year.
Figure 5.3.1 shows the progression of the standard Southern Oscillation Index (SOI) over the past 12 months from July 2022 to July 2023. The SOI has remained in negative territory and at low values over the past four months, dropping to -18.5 in May. The average SOI for the past two months has been -7 or lower. While the SOI is an important indicator for tracking tropical pressure changes, a broader range of atmospheric and oceanic conditions need to be considered when assessing ENSO status. This includes winds, cloud, ocean currents, surface and sub-surface ocean temperatures, and the outlook over the next few months.
Figure 5.3.1 Monthly time series of the SOI-BOM from July 2022 to July 2023(Source:
http://www.bom.gov.au/climate/enso/soi/)
Another commonly used measure of El Niño is called the Oceanic Niño Index (ONI). Figure 5.3.2shows the progression of several ONI values and their locations. In June 2023, the values for the three key NINO indices were: NINO3 1.33°C, NINO3.4 0.89°C, NINO4 0.67°C. The May and June data indicate the gradual warming of the tropical Pacific with sea surface temperatures approaching or exceeding historical averages.
Figure 5.3.2 NINO Region Distribution Map(Source:
https://www.ncdc.noaa.gov/teleconnections/enso/sst)
In June 2023, sea surface temperatures (SSTs) across almost all the tropical Pacific equatorial region were above average. The anomalous warmth in the eastern tropical Pacific was more than 4°C above average, with positive anomalies extending to the far eastern areas near the South American coast.
Closer to Australia, the Coral Sea continued to experience anomalously warm SSTs, more than 1.2°C above average for much of the region. Warm SST anomalies also persisted in the southern Tasman Sea, extending from southeast of Australia to around the south of New Zealand's South Island. Cool anomalies less than 1.2°C below average remained around the western Australian coastline.
Figure 5.3.3 Monthly temperature anomalies for January 2023 (Source:
http://www.bom.gov.au/climate/enso/wrap-up/#tabs=Sea-surface)
In summary, the tropical Pacific is currently undergoing a warming phase during the southern hemisphere winter. Central and eastern Pacific SSTs are currently above El Niño thresholds. Climate models indicate the central and eastern tropical Pacific may warm further. All surveyed models indicate temperatures will remain above El Niño thresholds at least until the end of this year. If the atmosphere responds to this warming, El Niño is likely to occur.
Table 5.3.1 ONI (°C) Anomaly Values from May 2023 to June 2023(Source:
https://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices)
If the emerging El Niño intensifies as predicted, its effects are likely to be felt across many global regions. An El Niño typically brings drier conditions to parts of Australia, Southeast Asia and southern Africa, increasing risks for agricultural production and wildfires. Wetter than usual weather is expected in South America, the southern U.S. and East Africa, which could lead to flooding concerns. The position of the jet stream over the Pacific and cyclone activity may also be impacted.