News – PH – Finally, climate science can better predict tropical Atlantic weather

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22nd February 2021

by Hyacinth C Nnamchi, the conversation

El Niño Southern Oscillation, or ENSO, an anomalous warming of surface waters in the tropical Pacific, is known to create unusual weather patterns around the world for months

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A similar, albeit lesser-known, circulation pattern, the Atlantic El Niño, dominates much of the Atlantic Ocean. The Atlantic El Niño phenomenon is analogous to the cycles that Pacific ENSOs produce as opposed to its Pacific counterpart, which is for Seasonal climate forecasts have proven invaluable, the Atlantic El Niño is hard to predict

The wide shifts in weather regimes known as ENSO occur when a massive swath of warm water forms off the coast of South America and extends into the central Pacific. The warmth of the water changes the airflow in the Pacific, which in turn changes weather conditions in Countries bordering the Pacific and beyond as air movements around the globe adapt to conditions in the Pacific Since the movement of warm and cold water across much of the Pacific is fairly slow, climatologists can see the arrival of ENSO and predict the strange weather conditions involved up to nine months in advance

This enables the affected countries to prepare for the heavy rainfall and floods in East Africa and the drought in southern Africa that an ENSO brings them at irregular intervals of 2-7 years

In many ways, the Atlantic El Niño is similar to the Pacific ENSO It follows a very similar pattern of changes in the ocean and the air movements above it It occurs when in the equatorial Atlantic region that borders the Guinea coast of Africa and becomes extending towards the northern parts of South America, forming warmer than normal water.This has been linked to heavy rainfall and flooding in the west African coastal area from Sierra Leone to southern Nigeria and droughts in the semi-arid Sahel

However, climatologists are struggling to understand why the Atlantic El Niño is formed. I recently led a study that offers new insights and gives hope for improved climate predictions and better preparedness

The air and sea water are essentially intertwined. Water in the ocean moves because winds blow on it. The air moves faster than the sea water below. The water reacts more slowly. In this way, the sea water forms a distinct movement pattern that the warmth Slowly redistributed over a period of several months Scientists can use climate models to track water movements and predict El Niño events

Since the El Niño patterns in the Atlantic and Pacific are thought to be similar, one would expect them to be similarly predictable, which is not the case.The Pacific pattern is relatively easy to predict while the Atlantic pattern is almost entirely unpredictable

And there are other important differences: The Atlantic events are of lesser magnitude and duration. The reasons for these differences have puzzled climatologists for decades

The key question is how important are the movements of warm and cold water to the origin of the Atlantic El Niño events

In our study, we examined the seasonal evolution of Atlantic warm events using data from a variety of sources, including in-situ observations, reanalysis (where observations were mixed using climate models), and satellite products

We have identified the movement of the Intertropical Convergence Zone, a band of low air pressure and heavy rainfall that stretches across the tropical Atlantic, as the reason for the short lifespan of the Atlantic Niño only when this zone is very close to or above the equator the interaction between air and ocean movement is strong enough to cause large climatic effects The intertropical convergence zone provides the right conditions in the air to favor the movement of warm and cold water in the ocean, however the fluctuations in sea surface temperature in the Atlantic are not strong enough to hold the intertropical convergence zone at the equator, as in the case of the Pacific ENSO

Computer climate simulations show that air movements, rather than seawater, are the key to Atlantic warm events A series of simulations was conventional and tried to take into account the detailed air and water movements.The second set reduced the complexity by simply using the ocean as a motionless plate of water a thickness of only 50 meters was modeled

This model has been formulated so that the ocean can absorb heat, give off heat, and evaporate moisture into the air, but the movements of warm and cold water in the ocean itself have been ignored, the atmosphere alone accounting for 63% of Atlantic El Niño events in these simulations from

This implies that the water movements observed in the Pacific Ocean are of lesser importance in the Atlantic The Atlantic is “naturally” less predictable

It is for this reason that our new findings, which establish a strong link to the intertropical convergence zone, are important. The zone needs to be represented more realistically in the climate models, which will make them more accurate and reliable

The African and South American countries on the equatorial Atlantic are heavily dependent on the ocean for social development, fisheries and tourism. They are severely affected by imponderables in weather systems. Accurate climate predictions are essential

Our results suggest that accurate predictions can be made for up to three months in this region. When this is realized, it will help in planning the adaptation to the severe weather conditions normally associated with Atlantic events

However, the equatorial Atlantic is a region with important uncertainties in the climate system: climate models have large errors and for many parameters there are large gaps in the observations that need to be closed. Closing the observation gaps is an important step in reducing climate model errors and to improve seasonal climate predictions

This article is republished by The Conversation under a Creative Commons license Read the original article

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Effects of climate change on oceans, oceans, El Niño

News – PH – At last, climate science can better predict tropical Atlantic weather
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Source: https://phys.org/news/2021-02-climate-science-tropical-atlantic-weather.html