This corresponds to stronger easterly trade winds, supporting La Niña conditions.īut during an El Niño, we see lower pressure in the eastern Pacific, over Tahiti, and higher pressure over Darwin. Positive SOI values mean the pressure over the Tahiti side is higher than over Darwin in Australia. The image below shows the location of the two pressure zones important for ENSO. The Southern Oscillation Index or SOI represents the difference in air pressure measured at Tahiti (French Polynesia) and Darwin (Australia). Thus, the ENSO phase directly responds to an atmospheric pressure change called the Southern Oscillation Index (SOI). Trade winds are steady and persistent winds, blowing towards (and along) the equator in both Hemispheres.īut the key here is not just in the winds, as pressure differences drive them. Global trade winds usually start or stop a certain ENSO phase by overturning the ocean surface layers and changing the ocean currents. Through this ocean-atmosphere system, the ENSO influences the weather globally.īut how can ENSO shift between cold and warm phases so rapidly? The simplest answer is that it happens because of a complex relationship between pressure, winds, and ocean currents. This way, ENSO strongly impacts the tropical rainfall and pressure patterns, affecting the ocean-atmosphere feedback system. At the same time, the air is descending in the western Pacific, causing stable weather and high-pressure conditions. Rising air in the eastern Pacific causes more storms and precipitation and lowers the pressure over that region. The following image below from NOAA Climate shows the typical circulation during an El Niño event, which will be the dominant phase for the next 10 months at least. But it is usually more influential during the peak of its phase in Fall and Winter. We can observe a global shift in pressure patterns during the emergence of an ENSO phase. These pressure changes translate into global circulation over time, affecting seasonal weather over both Hemispheres. But during a La Niña, the pressure over the equatorial Pacific rises, creating stable conditions and fewer storms. Besides the ocean temperatures, one of the main differences between the phases is the pressure patterns they promote, seen below as high (H) and low (L) pressure zones.ĭuring an El Niño, the pressure over the tropical Pacific drops, with more rainfall and storms in this region. The cold ENSO phase is called La Niña, and the warm phase is called El Niño. The last phase was a cold La Niña and it spanned three years. It then lasts until Spring, but some events can last up to two or three years. This affects the overall global circulation over time, changing the weather patterns worldwide.Ī (cold/warm) phase usually develops between late Summer and early Fall. But notice the regions 1+2, as they play an important role.Įach ENSO phase influences the pressure and weather in the tropics differently. The main area combines regions 3 and 4, seen in the image as the Nino 3.4 region. Regions 3 and 4 expand over the east and west tropical Pacific. The image below shows the ENSO regions across the tropical Pacific. Typically there is a phase change around every 1-3 years. Then you will see how El Niño is currently growing and how it is expected to influence the upcoming weather seasons, from the Hurricane season to the Winter 2023/2024.Įl Niño is a phase of the ENSO, which stands for “ El Niño Southern Oscillation.” This region of the equatorial Pacific Ocean regularly shifts between warm and cold phases. Ocean anomalies have a known impact on the atmosphere and our weather on smaller and larger scales, especially during the Winter season, when the pressure systems are strongest.įirst, we will quickly look at the connection between the oceans and the atmosphere. Based on the latest global anomaly data, this El Niño might be something we have never seen before in such an environment. A moderate to strong El Niño event is expected to occur, with global weather impacts in the second half of the year and over the Winter season of 2023/2024. El Niño is developing rapidly, with an official watch currently in effect, issued by NOAA.
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