Southern Oscillation Index

What Is The Southern Oscillation Index?

Meteorologists need to study different phenomena to be able to predict them and help people prevent suffering from damage.

For example, if they know when certain things might happen, they can alert the population in that area. The Southern Oscillation Index is a good example of that since it indicates the el Niño and la Niña occurrences.

Therefore, if you want to know about the Southern Oscillation Index, read on. Remember to share the guide with your family and friends so they also learn everything they want about the index, the el Niño and la Niña phenomena, how they originate, and more.

What Is the Southern Oscillation Index?

The Southern Oscillation Index is a description of the air pressure in Tahiti and Darwin, Australia. Also known as the SOI, it is the average per month that represents standardized sea level during each station.

On many occasions, the tropical eastern part of the South Pacific Ocean experiences high-pressure levels, whereas the East Indian Ocean has low pressure.

However, in some years, the opposite occurs: the eastern Indian Ocean experiences high pressure, while the South Pacific Ocean’s pressure is immensely low. That phenomenon is known as the Southern Oscillation.

To measure the different air pressures, the Southern Oscillation Index determines large-scale fluctuations between Tahiti and Darwin.

Southern Oscillation Index Calculation

The Southern Oscillation Index Calculation includes knowing monthly or longer averages since daily fluctuations often indicate smaller phenomena.

To calculate the index, you need to have the information and use a specific formula. The results point to el Niño and la Niña occurrences. For example, sustained values below eight mean el Niño, whereas positive values above eight indicate la Niña.

El Niño, la Niña Occurrences, and the Southern Oscillation Index

El Niño and la Niña occurrences are immensely important to understand the Southern Oscillation Index and its calculation.

During the 1920s, two important meteorologists identified specific air pressure fluctuations between the East Indian Ocean and the South Pacific Ocean. After naming it “Southern Oscillation,” the two meteorologists opened the path for further investigations on the matter.

Years later, the Southern Oscillation was linked to the Niño and la Niña occurrences, since it indicates the atmospheric pressure during the episodes.

El Niño and la Niña happen every few years, and they are the two phases of one meteorological phenomenon, called El Niño-Southern Oscillation or ENSO.

The origin of El Niño-Southern Oscillation occurs when the winds and the temperatures of the sea surface start varying over the tropical eastern area of the Pacific Ocean. Consequently, that affects many parts of the tropics and subtropics.

El Niño refers to the warming phase of the temperature of the sea and high surface pressure, whereas La Niña is in the cooling stage and has low pressure on the surface.

When the phenomenon occurs, the two periods often last a few months. Nonetheless, the intensity varies a lot depending on the year of the happening.

El Niño and la Niña are also related to the Walker circulation, which is a result of the high-pressure area over the Pacific Ocean, and the low-pressure one over Indonesia.

When the Walker circulation weakens, el Niño appears and generates high temperatures. On the other hand, when the circulation strengthens, la Niña occurs and temperatures start dropping.

Although el Niño and la Niña phenomena and the Southern Oscillation have been studied for a century, there is still no specific way to know why they occur. So far, they remain a wonder to many meteorologists and other experts.

Furthermore, even though el Niño and la Niña often happen during the same year, they don’t need to occur together. On the contrary, an el Niño episode can happen on its own.

Many people have started to believe that the el Niño and la Niña occurrences are a consequence of climate change, but that is not the case. They are natural meteorological happenings that the world cannot avoid. In other words, they can’t be affected by human actions.

Finally, el Niño and la Niña occurrences are crucial for meteorologists because they are responsible for harsh weather conditions in certain areas. South Africa, South America, Central America, South East Asia, East Africa, and the Pacific Islands are the most affected.


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