When the normally dry Apurímac near Lima, Peru swept away almost everything Carmen owned, she complained, “There are so many of us, so many. I am not the only one. Further north, heavy rains temporarily turned part of the coastal desert of Sechura into the second largest lake in Peru, which covers around 5,000 km 2 in other parts of the world. Intense cyclones and severe droughts have caused famine, plague, forest fires and damage to plantations, properties and the environment. What was the cause of all of this? Many point to El Niño, which emerged from the tropical or equatorial Pacific in late 1997 and has been running for about eight months.
What exactly is El Niño? How is that developing? Why are its effects so widespread? Can we accurately predict when it will next occur and possibly reduce the impact on life and property?
Everything starts with a warming of the water
"El Niño is actually just the flow of hot water that occurs every two to seven years in Peru," says Newsweek magazine. Seafarers on the Peruvian coast have noticed this warming for over a hundred years. Since these warm currents usually arrive around Christmas, they were called El Niño, the Spanish name for the baby Jesus.
The warming of the waters near the coast of Peru means increased rainfall for this country. The rains cause desert flowering and livestock development. When it is heavy, rains also cause flooding in the area. In addition, the top layer of warm seawater prevents cooler, nutrient-filled water from leaking out. As a result, many marine animals and even some birds migrate in search of food. The effects of El Niño can then be felt elsewhere on the Peruvian coast. * *
Born of wind and water
What causes the unusual rise in sea temperature near the Peruvian coast? To understand this, let's first consider the gigantic cycle, known as the Walker's cycle, that exists in the atmosphere between the eastern and western tropical Pacific. * As the sun warms the upper water table in the west near Indonesia and Australia, hot, humid air rises into the atmosphere, creating a low pressure system near the surface of the water. The rising air cools and loses its moisture, causing rain to enter the region. Dry air is driven east by winds from the upper atmosphere. As it moves east, the air becomes colder and heavier and begins to flow when it reaches Peru and Ecuador. This results in a high pressure system near the sea surface. At low altitudes, air currents, so-called trade winds, flow westwards back to Indonesia, thus completing the loop.
How do trade winds affect the surface temperature of the tropical Pacific? “These winds usually act like a breeze on a small lake,” explains Newsweek. “Hot water collects in the western Pacific, so that the sea surface is up to 60 centimeters higher and 8 ° C warmer there than in Ecuador, for example. "In the Eastern Pacific, the coldest water is full of nutrients beneath the wells, which is why marine life thrives. As a result, sea surface temperatures are warmer in the east than in the west during normal and other El Niño years.
What changes in the atmosphere cause an El Niño? "For reasons that scientists still don't understand," says National Geographic, "the trade winds decrease or even disappear every few years." When these winds subside, the hot water that has accumulated near Indonesia returns east, increasing sea surface temperature in Peru and elsewhere in the east. This movement, in turn, affects the atmospheric system. "The warming of the eastern tropical Pacific Ocean weakens Walker's circulation and causes the convective zone of heavy rain to move east, west into the central and eastern tropical Pacific," says a reference book. Thus, the climatic conditions in the entire equatorial Pacific are affected.
Like a stone in a stream
El Niño can also change weather patterns over long distances from tropical Pacific water currents. How? "Or what? Using the atmospheric circulatory system as a means. The dramatic effects of a local disturbance in atmospheric circulation can be compared to how a rock in the middle of a creek can cause ripples across the stream. Dense rain clouds piling over the warm tropical waters." Ascending ocean form a rocky obstruction in the atmosphere that affects weather conditions for thousands of people.
At higher latitudes, El Niño amplifies and modifies the fast wind currents in the east, known as jet currents. Jet streams direct the flow of most storm systems in these latitudes. Increasing and changing the jet currents can also intensify or moderate the seasonal climatic conditions. For example, winters in El Niño in the northern parts of the United States are generally milder than normal, while in some southern states they are wetter and cooler.
How predictable?
The effects of individual storms can only be predicted a few days in advance. Is it the same for attempts to predict an El Niño? No. Instead of taking short-term weather events into account, El Niño's forecast includes months of abnormal weather conditions in large areas. And climatologists have had some success predicting El Niño.
For example, the forecast for El Niño 1997-98 was published in May 1997 - about six months before it rose. There are now 70 anchored buoys across the tropical Pacific that measure surface wind conditions and ocean temperatures to a depth of 500 m. When this data is fed into computer models of the climate, they generate weather forecasts.
El Niño's early warnings can really help people prepare for the expected changes. For example, since 1983, Peru's El Niño projections have encouraged many farmers to raise livestock and plant crops that are suitable for more humid conditions while fishermen have stopped fishing and started harvesting shrimp, which is supplied with warmer water will. Yes, accurate forecasting combined with prior preparation can lower El Niño's human and economic costs.
Scientific research into the processes that control the earth's climate confirms the accuracy of the inspired words recorded by King Solomon of ancient Israel about 3,000 years ago. He wrote: “The wind goes south and goes north. In a circle it turns continuously and in a circle the wind returns. "(Ecclesiastes 1: 6) Modern man has learned a great deal about weather conditions by studying wind and ocean currents. We can use this knowledge by paying attention to warnings about events like El Niño.