Japan's fastest supercomputer used to simulate clear air turbulence

The researchers believe this will help build a more predictive model to prevent future incidents of dangerous clear air turbulence.
Sejal Sharma
Representational image
Representational image

Jetlinerimages/iStock 

Besides poor visibility, icing, and bird, mid-flight turbulence is one of the most common causes of aircraft accidents.

Clear air turbulence (CAT) is a truly significant aviation hazard. It's invisible, mostly cloud-free, hard to predict, and the most dangerous type of turbulence. It can be caused by jet streams, gravity waves, or cumulus clouds. 

Because CATs appear very suddenly, we need more accurate turbulence forecasts and real-time predictions. Invisible CATs have been visualized with simulations; however, it’s uncertain how well turbulent eddies can be realistically reproduced and whether they threaten aircraft.

And now, a research group from Nagoya University in Japan has produced clear air turbulence in a real case using a numerical weather prediction model on the country’s fastest supercomputer.

Invisible turbulence

The researchers believe this will help build a more predictive model to prevent future incidents of clear air turbulence.

On December 30, 2020, several encounters with CAT were reported near Tokyo. The scientists reproduced the turbulence after employing an operational forecasts model, which led them to believe that the CAT was not merely a numerical artifact but very realistic. The signs of similar turbulence were also found in the original flight data.

“Around Tokyo, there is a lot of observational data available to validate our results,” said Dr. Ryoichi Yoshimura of Nagoya University. “There are many airplanes flying over the airports, which results in many reports of turbulence and the intensity of shaking. Atmospheric observations by a balloon near Tokyo were also used. The shaking data recorded at that time was used to show that the calculations were valid.”

Creating realistic eddies in the free atmosphere will help understand the turbulence itself and use its applications in aviation, like adjusting flight levels if the presence of active turbulence is known in advance. 

“The results of this research should lead to a deeper understanding of the principle and mechanism of turbulence generation by high-resolution simulation and allow us to investigate the effects of turbulence on airplanes in more detail,” said Yoshimura. 

“LES would provide a smart way of flying by providing more accurate turbulence forecasts and real-time prediction,” he added.

The research was reported in the journal Geophysical Research Letters.

Study abstract:

A clear air turbulence (CAT) occurred on 30 December 2020 over Tokyo, Japan. The CAT was largely generated by breaking Kelvin-Helmholtz (KH) instability waves in the free atmosphere. A regional numerical weather prediction model simulated the event with fine resolution (35 m). Onboard-recorded flight data and a flight simulation were utilized to validate the meteorological simulation. The locations of the reproduced strong turbulence agree well with the regions where flights encountered turbulence on that day. In a simulation with the finest resolution, the KH waves and their breaking were resolved. When the resolution was finer, the turbulent eddies were stronger, causing meteorological effects on the airplanes. The response of a virtual airplane to the simulated turbulence was estimated using a flight simulation. By comparing onboard-recorded data with virtual flight data, we confirm that turbulent eddies are reasonably reproduced.

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