Predicting how strong an emerging typhoon will become is extremely important in minimizing damage. However, accurate prediction of a typhoon in its rapid intensification phase is still a difficult task. One of the main reasons for this is that active eddies are as small as a few hundred meters, yet the resolution of general numerical computations is as coarse as a few kilometers.
A research team led by Associate Professor Junshi Ito of the Graduate School of Science at Tohoku University successfully reproduced a single typhoon from the weak vortex stage to a very strong typhoon over about 4 days at an ultra-high resolution of 100 meters using Fugaku. The team divided the huge computational space with a 2,000-km-square area into 60 vertical layers with a horizontal resolution of 100 meters. They performed numerical computations either directly for relatively large eddies or by modeling the effect for smaller eddies. They also performed low-resolution computations with a horizontal resolution of 2 km under the same conditions and compared temporal changes in minimum pressure, maximum wind speed, maximum wind radius, etc.
The results showed that, while the maximum intensity was roughly the same for both, the beginning of rapid intensification was delayed by about one day in the ultra-high-resolution computations. The team examined in detail the distribution of tiny eddies less than 1 km in radius as well as eddies about 10 km in radius that form around the eye of the typhoon. They found that these eddies prevent air flow into the center of the typhoon and delay the start of rapid typhoon intensification.
This research indicates that the conditions that influence the timing of rapid typhoon development may be a collection of small eddies that have not been directly handled in previous computations. This finding may provide an important clue for improving the prediction of typhoon intensity in the future.
(Article: Masanori Nakajo)
