Causes Of El Nino
Before we look at the causes of El Nino, let’s take a look at what is the El-Nino.
What is the El-Nino
The El-Nino, otherwise known the El-Nino-Southern-Oscillation (ENSO), is a phenomenon that has been going on for centuries. However, it is only recently that it has become much better understood. As a result, we are becoming better at predicting when it may occur, how strong the El-Nino may be, how long it may last and what its effects might be.
The term El-Nino is Spanish for “Christ Child”. This is because the phenomenon usually occurs around the Christmas season. It was during this time of the year that fisherman first discovered how the ocean currents will become much warmer near the coasts of Peru and Ecuador. During this period, the fishermen also observed that the fishes were much less in abundance than usual.
We now use the term El Nino to refer to the large scale warming of sea surface temperatures that occurs in the Pacific Ocean every three to six year. Typically, an El-Nino lasts for nine to twelve months, but can last for as long as 18 months. During this period, the weather across the world is dramatically affected.
Because an El Nino does not occur on a regular basis and has such a worldwide impact, it is important to understand the causes of EL-Nino and accurately predict its appearance. As a result, numerous climatic models, forecasting models and statistical models have been designed to try to predict the causes of El-Nino and when one will occur. This task has gotten more effective since with advancement in computer technologies and will continue to do.
Read more about the El-Nino and its opposite twin, the La Nina.
The opposite of El Nino – what normally happens
As for what are the causes of El-Nino, first, we have to take a look at the winds blowing across the Pacific Ocean.
Under normal non-El-Nino circumstances, the trade winds blow from east (cooler and of higher pressures) to west (warmer and of lower pressure) along the Equator in the Pacific Ocean as a result of temperature differences along the equator. The larger the temperature and pressure difference, the stronger the winds blowing to the west (otherwise known as easterlies). In turn, these winds blow the warmer waters from the east (areas like Peru) to the western coasts (areas like Indonesia and Australia) of the Pacific Ocean. In fact, as a result of a very strong wind, about half a meter of water could pile up in the western part of the Pacific, resulting in a deep warm pool in the west.
With the warmer waters in the east moving toward the west of the Pacific Ocean, the decrease in surface water volume in the east draws up the deeper eastern to the surface. This is a process called upwelling where the deeper cooler water that is not warmed by the sun comes up from the ocean depths. This process results in water of about 8 degrees Celsius warmer in the west than in the east.
The warmer waters in the western coast then bring rainfall to areas such as Indonesia and coastal Australia, while areas like Peru remain dry and cool.
Causes of El Nino
However, in an El Nino event, the opposite is true.
One of the first signs of an El Nino is the weakening of west-bound trade winds, or when the trade winds reverse direction and head toward the eastern coasts of the Pacific Ocean instead. Norwegian America meteorologist, Jacob Bjernes, suggested the weakening of the trade winds could be a result of an abnormal warm spot in the eastern pacific where it should be cool. As a result of such warming in the east, the temperature difference between eastern and western Pacific drops, and the strength of the west-bound trade winds reduces. The water that gets piled up in the western Pacific begins to move back to the east.
The warmer water in the east further weakens the surface winds to the west. As these winds relax and less warm water is displaced to the west, the eastern ocean will get much warmer resulting in even weaker westward winds and an even warmer eastern ocean. Warm water then gets piled up in the east (areas like Peru) instead. Rainfall follows the warm water eastwards, bringing floods to the normally dry areas in Peru, and droughts in the normally wetter regions like Indonesia and Australia. This process is a classic hallmark of causes of El Nino. Read more about the effects of El-Nino.
Triggering causes of El-Nino
Today, what exactly triggers the start of an El Nino is still being investigated.
The Earth and Environmental Sciences Department in the Columbia University describes the movement of warm air along the equator and the corresponding piling up of warm waters over the Pacific Ocean coasts as oscillating between the east and west coasts. Hence, the name El-Nino-Southern-Oscillation. It is believed that this oscillation is made possible by the difference in speed between the eastward Kelvin waves and the westward Rossby waves. Travelling against the Earth’s Coriolis force, Rossby waves travel at about 3 times slower than Kelvin waves. When the water movements oscillate to the east, El-Ninos (ENSO’s warm phase) are born. When the water movements oscillate to the west, the opposite of El-Ninos – La Ninas (ENSO’s cool phase) – are born.
Along the same vein, the Public Broadcasting Services (PBS), a private, not for profit educational media corporation, reported of scientists’ postulation that the triggering causes of El Nino is the very accumulation of warm waters in the west under normal circumstances (i.e. during an anti-El-Nino, or a La Nina). The volume of water in the east (containing massive amounts of energy) builds up to a certain point, and like a pendulum that has reached the highest point of its swing reverses it direction and swings back, the built up water in the west begins flowing backwards to the east. In other words, one of the triggering causes of El-Nino is the death of its opposite twin, the La Nina, and vis versa.
Global Warming and the causes of El-Nino
According to the National Oceanic and Atmospheric Administration (NOAA) , National Climate Data Center, the El Nino phenomenon has been around for thousands, if not millions of years. As such, it is unlikely that the causes of El-Nino is the recent global warming. However, warmer global temperatures have been found to enhance the El-Nino event. There are some evidences that the El-Nino has become more frequent and intense in recent years as a result of global warming.
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