Hurricanes are powerful storms that can cause widespread damage and devastation on land. But they also have a significant impact on the ocean, where they draw their energy from warm sea surface temperatures.
Hurricanes can mix the ocean's surface layer, creating cooler waters that reduce the storm's intensity.
But they can also push heat deeper into the ocean, where it can be stored for long periods and affect the global climate.
In a new study, published in the journal Nature Communications, researchers from the University of California, San Diego, and Brandeis University have used real-time measurements and numerical simulations to show how hurricanes can generate underwater waves that transport heat to depths of more than 1,000 feet (300 meters).
The study has implications for understanding how hurricanes influence ocean warming and circulation.
How hurricanes generate underwater waves
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When a hurricane passes over the ocean, it creates strong winds that generate waves at the surface, as per Phys.org.
These waves interact with the ocean's stratification, which is the vertical variation of density due to changes in temperature and salinity.
The surface layer is usually warmer and less dense than the deeper layer, creating a boundary called the thermocline.
As the surface waves propagate downward, they encounter the thermocline and reflect back to the surface.
However, some of the wave energy can cross the thermocline and generate internal waves in the deeper layer.
These internal waves are similar to surface waves, but they travel along density surfaces rather than along the air-water interface.
Internal waves can carry heat, momentum, and nutrients across different depths and regions of the ocean.
They can also affect marine life by creating oscillations in light, temperature, and pressure that influence the behavior and distribution of organisms.
The researchers used an instrument called a microstructure profiler to measure ocean turbulence and internal waves in the Philippine Sea for two months in 2018.
They deployed the instrument from a research vessel and let it free-fall up to 1,000 feet (300 meters) below the surface.
The instrument recorded temperature, salinity, pressure, and velocity fluctuations at high resolution.
The researchers compared the measurements before and after three major typhoons passed over the region.
They found that typhoons enhanced the generation of internal waves by increasing the amplitude and frequency of surface waves.
They also found that the internal waves propagated downward and horizontally, reaching depths of more than 1,000 feet (300 meters) and distances of more than 60 miles (100 kilometers) from the storm's track.
The researchers used a numerical model to simulate how internal waves affect ocean heat transport and storage, as per the Conversation.
They ran two scenarios: one with hurricanes and one without hurricanes. They compared the results over a period of 10 years.
The model showed that hurricanes increased the amount of heat that was transferred from the surface layer to the deeper layer by about 20%.
This heat was stored in a layer between 650 feet (200 meters) and 1,650 feet (500 meters) below the surface, where it could not easily return to the atmosphere.
The model also showed that hurricanes increased the amount of heat that was transported horizontally by deep ocean currents by about 10%.
This heat was carried to distant regions, such as the eastern Pacific or the Indian Ocean, where it could resurface and affect the local climate.
The researchers estimated that hurricanes contributed to about 5% of global ocean warming over the past decade.
They also suggested that hurricanes could have a larger impact on regional ocean warming and circulation patterns.
The researchers concluded that hurricanes play an important role in shaping ocean heat distribution and dynamics.
They recommended that future studies should include hurricane effects in ocean models to improve climate predictions and projections.
