New research – Ars Technica shows that hurricanes drive heat deeper into the ocean than scientists realized

Zoom in / Satellite data showing the heat signature of Hurricane Maria over warm surface waters in 2017

When a hurricane hits the ground, the devastation can be visible for years or even decades. Less obvious, but also powerful, is the impact hurricanes have on the oceans.

in New studyWe show through real-time measurements that cyclones don’t just disturb water at the surface. They can also drive heat deeper into the ocean in ways that can trap it for years and eventually affect regions far from the storm.

Heat is the main ingredient in this story. It has long been known that hurricanes It gains its energy from warm sea surface temperatures. This heat helps Humid air near the ocean surface elevation Like a hot air balloon, cloud formation is taller than Mount Everest. This is why hurricanes generally form in the tropics.

What we found out is that hurricanes ultimately help warm the ocean as well, by enhancing its ability to absorb and store heat. And that could have far-reaching consequences.

How do hurricanes get energy from ocean heat?
Zoom in / How do hurricanes get energy from ocean heat?

When hurricanes mix heat into the ocean, that heat doesn’t just float to the surface in the same place. We showed how the underwater waves produced by a storm can drive heat Almost four times deeper than mixing alone, and sending it to a depth where the heat is trapped farther from the surface. From there, deep-sea currents can carry it thousands of miles. A hurricane traveling through the western Pacific Ocean and battering the Philippines could end up supplying the warm waters that heat Ecuador’s coast years later.

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At sea, looking for hurricanes

For two months in the fall of 2018, we lived aboard the Thomas G. Thompson research vessel recording how the Philippine Sea responds to changing weather patterns. like Ocean Scientistswe study turbulent mixing in the ocean and hurricanes and other tropical storms that generate this turbulence.

The skies were clear and the winds calm for the first half of our experience. But in the second half, three major hurricanes — as hurricanes are known in this part of the world — stirred up the ocean.

This shift allowed us to directly compare ocean movements with and without the impact of storms. In particular, we were interested in learning how turbulence beneath the ocean’s surface helps transfer heat to the ocean depths.

We measure ocean turbulence with an instrument called the Microstructure Profiler, which drops freely from nearly 1,000 feet (300 meters) and uses a probe similar to a phonograph needle to measure the turbulent motions of the water.

What happens when a hurricane comes

Imagine the tropical ocean before a hurricane passes over it. On the surface is a layer of warm water, warmer than 80 °F (27 °C), heated by the sun and extending about 160 feet (50 m) below the surface. Under it are layers of cold water.

the temperature difference Between the layers keeps the water separate and virtually unable to affect each other. You can think of it like dividing between the oil and vinegar in an unshaken bottle of salad dressing.

When a hurricane passes over the tropical ocean, its strong winds help move the boundaries between the layers of water, much like someone shakes a bottle of salad dressing. In this process, cold deep water is mixed from below and warm surface water is mixed to the bottom. This cools surface temperatures, allowing the oceans to absorb heat more efficiently than normal in the days after a hurricane.

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For more than two decades, scientists Discuss Whether the warm waters with which cyclones mix downstream warm ocean currents and thus shape global climate patterns. The crux of the question was whether hurricanes can pump heat deep enough that it stays in the ocean for years.

These illustrations show what happens to ocean temperature before, during, and several months after a hurricane passes.
Zoom in / These illustrations show what happens to ocean temperature before, during, and several months after a hurricane passes.

By analyzing subsurface ocean measurements taken before and after three hurricanes, we found that underwater waves transfer heat nearly four times as much into the ocean than direct mixing during a hurricane. These waves, generated by the tornado itself, transport heat deep enough that it cannot be easily released back into the atmosphere.

Heat fallout in the ocean depths

Once this heat is captured by large-scale ocean currents, it can be transported to distant parts of the ocean.

The heat delivered by the hurricanes we studied in the Philippine Sea may have flowed to the coasts of Ecuador or California, according to current patterns that move water from west to east across the equatorial Pacific.

At this point, the heat can be mixed back to the surface with a mixture of shallow streamsAnd rising And disturbed mixing. Once the heat approaches the surface again, it can warm the local climate and affect ecosystems.

For example, corals are particularly sensitive to prolonged periods of heat stress. El Niño events are the usual reason behind this Coral bleaching in Ecuadorbut the extra heat from the hurricanes that we observed may be contributing to coral stress and coral bleaching far from where the storms originate.

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Coral reefs are an essential habitat for fish and other marine life, but they are threatened by rising ocean temperatures.
Zoom in / Coral reefs are an essential habitat for fish and other marine life, but they are threatened by rising ocean temperatures.

It is also possible for excess heat from hurricanes to remain within the ocean for decades or more without returning to the surface. This will actually have a mitigating effect on climate change.

Because hurricanes redistribute heat from the ocean’s surface to greater depths, they can help slow the warming of Earth’s atmosphere by keeping heat in the ocean.

Scientists have long thought of hurricanes as extreme events fueled by ocean heat and shaped by Earth’s climate. Our findingspublished in Proceedings of the National Academy of Sciences, adds a new dimension to this problem by showing that the interactions go both ways—hurricanes themselves have the potential to warm the ocean and shape Earth’s climate.

Conversation

Noel Gutierrez BrizuelaPhD Candidate in Physical Oceanography, University of California, San Diego And Sally WarnerAssociate Professor of Climate Sciences, Brandeis University. This article has been republished from Conversation Under Creative Commons Licence. Read the The original article.

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