How Japan's Supercomputer Simulates Clear Air Turbulence
Sophia Kumar
Clear air turbulence (CAT) is a phenomenon that can cause sudden and violent shaking of an aircraft even on a cloudless day. It is caused by invisible fluctuations in air currents that are difficult to detect and predict. CAT poses a serious threat to aviation safety, as it can injure passengers and crew members, damage aircraft, and disrupt flight operations.
To better understand and forecast CAT, researchers need to model it using sophisticated computational techniques that can simulate the complex interactions of air flows at different scales. However, such simulations require enormous amounts of computing power that are beyond the reach of most conventional computers.
That's why a research group from Nagoya University turned to Japan's most powerful supercomputer, Fugaku, to perform an ultra-high-resolution simulation of CAT above Tokyo's Haneda airport in winter. Fugaku is currently ranked as the world's second fastest supercomputer, capable of performing over 400 quadrillion calculations per second.
Using Fugaku's immense computational power, Dr. Ryoichi Yoshimura of Nagoya University and his collaborators from Tohoku University reproduced cases of CAT that occurred on December 16 and 17 in 2016. They used a technique called large-eddy simulation (LES), which resolves the large-scale eddies that are responsible for turbulence generation.
They found that the CAT was caused by the collapse of a specific type of atmospheric wave called Kelvin-Helmholtz instability wave. This wave forms when two layers of air with different velocities interact at their interface, creating a wave-like pattern that eventually breaks down into smaller vortices.
The researchers compared their simulation results with data recorded by aircraft that flew through the turbulent region. They found that their simulation accurately captured the wind speed disturbance and its spatial distribution. They also confirmed that their simulation could reproduce other cases of CAT with different weather conditions and locations.
The study, published in the journal Geophysical Research Letters on July 12, 2023, demonstrates the potential of Fugaku to advance our understanding and prediction of CAT. It also shows how supercomputing can help improve aviation safety and efficiency by providing more reliable information for pilots and air traffic controllers.
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