Probing The Ocean Before The Storm

A study by researchers in Hong Kong and London suggests that atmosphere climate models including ocean systems are better in predicting storm behavior

Asian Scientist Magazine (Aug. 30, 2022) — In 2017, Typhoon Hato affected more than 700,000 people while causing an economic loss worth $4 billion USD in South China. From a small circular motion on the horizon, Typhoon Hato evolved into a gargantuan beast damaging around 6,500 houses in coastal areas.  The storm intrigued researchers in the City University of Hong Kong and Imperial College London, who decided to study the factors influencing the evolution of Typhoon Hato.

A team of researchers led by Johnny C. L. Chan published their findings in Advances in Atmospheric Sciences and found that the three components — ocean, wave, and atmosphere — are interrelated and affect the strength of a typhoon when it’s about to reach the shore.

According to Dr Chan, a typhoon needs energy to spin up into a storm. This energy is obtained from the ocean in the form of heated water. “Our previous study showed that the ocean water temperature near the shore increased quite a bit just before the typhoon passed over this warm water and then intensified,” Chan explained in an interview with Asian Scientist Magazine. “But the ocean is not changing; it’s there just like a hot plate,” acting as a medium to transfer energy to a typhoon.

His team postulated that there are other sources supplying the energy to the ocean. To find out if that were the case, the researchers upgraded the atmosphere-only model system they built in 2018. “In the real atmosphere-ocean system, the atmosphere interacts with the ocean so we need to have a system that has both the atmosphere and the ocean together,” Chan added. By including ocean modelling and waves simulation components to the system, the researchers re-evaluated the 642 tropical cyclones that occurred in South China during 1990-2010.

The team found that the intensity of the simulated typhoons is similar in the atmosphere-only and atmosphere-ocean systems, so the team divided the typhoons into two categories based on their speed to “further diagnose the impact of ocean coupling on the intensity simulation”: the weaker group which moves slower and the stronger group with faster movement.

They found that the sun provides heat to the sand in coastal areas, therefore the shore with an extensive continental shelf will have warmer ocean water temperature as the heat from the sand is transferred to the water. “For the case of Hato, the reason why the ocean water temperature went up is because there is no cloud cover,” Chan explained. Without this cloud cover, the storm picks up energy readily available from the ocean and causes severe damage to coastal areas. Meanwhile, storms with extensive cloud cover in the surrounding tend to move slower as “the sun cannot penetrate through the clouds to heat up the water below.”

The results from this atmosphere-ocean computer modelling can be translated to two different perspectives. For forecasters, by looking at the cloud covers during a storm, they can anticipate the possibility of instant intensification.

“It’s important that weather centers run a model that includes the ocean and the waves so that the representation would be more realistic,” said Chan. Subsequently, forecasters can inform the results of these predictions to people living in coastal areas ahead of landfall so they are better prepared to weather the storm.

Source: City University of Hong Kong; Image: Pixabay

The paper can be found at: Importance of Air-Sea Coupling in Simulating Tropical Cyclone Intensity at Landfall 

Septia Nurmala is a recent graduate from Pharmacy Professional Degree program, Universitas Indonesia where she focused on how medicines are regulated. As a writer who covers just about anything—from molecular scale to population level, she hopes to showcase the human narratives driving scientific discoveries and increase accessibility.

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