A research team from Nagoya University in Japan found that larger, slower-moving typhoons are more likely to be resilient to global warming. But compact, faster-moving storms are more likely to be vulnerable. These findings suggest an improved method for estimating typhoon strength under global warming conditions. The report was published on: Geophysical Research Letters.

Tropical cyclones are among the most dangerous weather systems in the world, causing disruption, damage and death across East Asia. As global temperatures increase, the danger of typhoons also increases. However, it is becoming increasingly difficult to predict the strength and nature of such storms. Understanding changes in ocean response is critical to mitigating the worst impacts of typhoons. One way to understand tropical cyclones is to examine the relationship between the atmosphere and the ocean. The relationship between the ocean and atmosphere affects weather, ocean circulation, and climate variability.

This is especially important for typhoons, as the intensity of tropical cyclones is associated with an increase in sea surface temperature (SST). As the size of the cyclone increases, SST decreases and its intensity becomes limited. However, under global warming conditions, SST is higher. As a result, the typhoon may last longer.

“The increase in sea temperatures is a cause for concern because a typical fast-moving storm, such as Typhoon Faksai in 2019, caused severe damage in eastern Japan,” lead researcher Sachi Canada said. “Our results suggest that the intensity of such typhoons may increase under global warming conditions.”

To understand how global warming might affect typhoons, Canada and fellow researcher Hidenori Aiki investigated the buffering effect of the atmosphere-ocean coupling on typhoons. They used a state-of-the-art weather system simulator, an atmosphere-ocean model called CReSS-NHOES, to evaluate the impact of atmosphere-ocean coupling on changes in the intensity of severe typhoons. CReSS-NHOES combines the CReSS cloud simulation model developed at Nagoya University with the NHOES oceanographic model developed by the Japan Agency for Marine Science and Technology.

Researchers used CReSS-NHOES to study four strong but different-magnitude typhoons in recent years: Trami (2018), Faksai (2019), Hagibis (2019), and Haishen (2020). All of these typhoons were devastating; Trami and Faksai caused billions of dollars in damage and Hagibis killed 118 people.

Canada and Aiki considered three scenarios: pre-industrial climate, 2°C increase in TPM, and 4°C increase in TPM.

“We found that the magnitude of typhoon strengthening per 1°C under TPM varies significantly from typhoon to typhoon,” Canada said. said.

He was surprised by the change in hPa, a unit of pressure used in meteorology to measure atmospheric pressure and represents the strength and intensity of a storm, noting: “A typhoon like Trami only strengthens by 3.1 hPa, while Faksai strengthens by 1 hPa. 1 in TPM °C increased to 16.2 hPa”.

The results of this study show that the atmosphere-ocean coupling effect reduces changes in storm intensity associated with global warming. However, typhoons of different sizes may be affected differently. Storms with large eyes and low velocities cause SSTs to fall near their centers, hindering their development. However, storms with small eyes and high movement speed move away from the formation of TPM. Such typhoons increase their intensity by keeping constant heat at their centers.

Using these findings, researchers created a new model to predict the impact of tropical cyclones. They used a simple parameter called dimensionless storm velocity (S0). Their model showed that S0 can distinguish between potentially destructive storms that are likely to intensify under global warming and storms that are resilient to the effects of global warming.

“Current climate change forecasts of typhoon intensity are conducted using coarse horizontal resolution models or atmospheric-only models that have difficulty reproducing the intensity and structure of strong typhoons,” Canada explains.

“Using a high-resolution coupled regional atmosphere-ocean model, this study can reproduce the intensity and structure of strong typhoons and the ocean response with high precision, so they are expected to contribute not only to the quantitative projection of typhoon intensity under warming conditions, climate, but also to the accuracy of current typhoon intensity forecasts.” It’s also improving.”