What is an Atlantic Ni帽a? How La Ni帽a's smaller cousin could affect hurricane season
The North Atlantic Ocean has been running a fever for months, with surface temperatures . But cooling along the equator in both the Atlantic and eastern Pacific may , particularly for vulnerable coral reef ecosystems.
This cooling comes from two climate phenomena with similar names: La Ni帽a, which forms in the tropical Pacific, and the less well-known Atlantic Ni帽a.
Both can affect the Atlantic hurricane season. While La Ni帽a , the less powerful Atlantic Ni帽a has the potential to reduce some of the hurricane risk.
We're and who study this type of climate phenomenon. It's rare to see both Ni帽as at the same time, yet in August 2024, . Let's take a closer look at what that means.
La Ni帽a and its cousin, Atlantic Ni帽a
La Ni帽a is part of the , a well-known climate phenomenon that has widespread effects on climate and weather around the world.
During La Ni帽a, sea surface temperatures in the tropical Pacific dip below normal. Easterly trade winds then strengthen, allowing more cool water to well up along the equator off South America. That cooling affects the atmosphere in ways that reverberate across the planet. Some areas become stormier and others drier during La Ni帽a, and the wind shear that can tear apart Atlantic hurricanes tends to weaken.
La Ni帽a and its warmer opposite, , oscillate .
A similar climate phenomenon, , occurs in the Atlantic Ocean but at a much smaller scale and amplitude. It typically peaks around July or August and tends to have a shorter duration than its Pacific cousin, and much more modest and local impacts. Atlantic Ni帽as generally have the of reduce region and increase rainfall in Brazil and the countries that surround the Gulf of Guinea, such as Ghana, Nigeria and Cameroon.
While much weaker than their Pacific counterpart, Atlantic Ni帽as can, however, partially counteract La Ni帽as by weakening summer winds that help drive the upwelling that cools the eastern Pacific.
Why are both happening now?
In July and August 2024, meteorologists that appeared to be the development of an Atlantic Ni帽a along the equator. The winds at the ocean surface had been weak through most of the summer, and sea surface temperatures there were , so signs of an Atlantic Ni帽a emerging were a surprise.
At the same time, waters along the equator in the eastern Pacific were also cooling, with there by October or November.
Getting a Pacific-Atlantic Ni帽a combination is . It's like finding two different pendulums that are weakly coupled to swing in opposite directions moving together in time. The combinations of La Ni帽a and Atlantic Ni帽o, or El Ni帽o and Atlantic Ni帽a are more common.
Good news or bad for hurricane season?
An Atlantic Ni帽a may initially suggest good news for those living in hurricane-prone areas.
Cooler than average waters off the coast of Africa can suppress the formation of African easterly waves. These are that can form into tropical disturbances and eventually tropical storms or hurricanes.
Tropical storms associated with warm sea surface temperatures. So, cooling in the tropical Atlantic could weaken this process. That would leave less energy for the thunderstorms, which would reduce the probability of a tropical cyclone forming.
However, NOAA takes all factors into account when , released in early August, and it still anticipates an extremely active 2024 season. in early to mid-September.
Two reasons are behind the busy forecast: The sea surface temperatures in much of the North Atlantic can strengthen hurricanes. And the expected development of a La Ni帽a in the Pacific tends to weaken wind shear鈥攖he change in wind speed with height that can tear apart hurricanes. La Ni帽a's much stronger effects can override any impacts associated with the Atlantic Ni帽a.
Exacerbating the problem: Global warming
The past two years have seen in the Atlantic and around much of the world's oceans. The two Ni帽as are likely to contribute some cooling relief for certain regions, but it may not last long.
In addition to these cycles, the global warming trend caused by rising greenhouse gas emissions is raising the baseline temperatures and can .
Provided by The Conversation
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