KIOST tracks Typhoon Soudel under the ocean surface, down to 2,000 meters

The Korea Institute of Ocean Science and Technology has measured changes in water temperature and salinity down to roughly 2,000 meters below the surface near the eye of Typhoon Soudel, the 18th named storm of the season. The institute deployed unmanned observation equipment into the typhoon's zone of influence — where high waves and strong winds make vessel access dangerous — to directly track ocean conditions during the storm's peak intensity.

KIOST announced Tuesday that its research vessel Isabu had begun field observations of Soudel in international waters east of the Philippine exclusive economic zone. Researchers conducting a scheduled voyage adjusted their route and observation plan after confirming the typhoon's formation and tracking its projected path.

Soudel formed near Guam on Wednesday and intensified into a very strong typhoon as it passed over warm ocean waters. It is currently forecast to move past the Okinawa island chain toward southeastern China.

The central focus of the observation mission is understanding how heat energy stored in the ocean changes before and after a typhoon passes through. That stored heat — measured as ocean heat content — is a key factor determining a typhoon's intensity.

KIOST is mapping the distribution of heat content in the upper ocean layer ahead of Soudel's approach to investigate how the ocean influences a typhoon's formation and development. After the storm passes, researchers plan to analyze how heat content and the temperature-salinity structure change, and to track how the ocean recovers to its pre-storm state.

Notably, a single Argo float — an unmanned observation device — gathered depth-specific water temperature and salinity readings near the typhoon's eye from 3 a.m. Sunday through 9 a.m. Monday, when Soudel was at peak intensity. The Argo float repeatedly ascends and descends to depths of roughly 2,000 meters, measuring the vertical distribution of temperature and salinity.

Direct ship-based observation in a typhoon's path is extremely difficult due to high waves and strong winds, making such data hard to obtain. To minimize researchers' exposure to high-risk sea areas while securing continuous data from the typhoon's formation through its dissipation, KIOST deployed multiple types of unmanned equipment.

Surface-drifting automatic observation buoys measure sea surface conditions and water temperature changes, while remotely operated wave gliders directly observe conditions at the ocean surface and in the marine atmosphere above it. By operating instruments assigned to different depths and roles simultaneously, the institute is building a three-dimensional picture of the typhoon's impact on the ocean.

KIOST plans to use the data collected at peak intensity to analyze how strong winds alter the upper ocean layer. The observations will also feed into research on typhoon-ocean interaction and efforts to improve typhoon forecast models.

"To accurately predict a typhoon's intensity, we need to observe not only the storm itself but also the state of the ocean, which supplies the typhoon with energy and water vapor," said Kim Seong-hun, director of KIOST's Ocean Climate Prediction Center. "This observation is highly significant because it allows us to build a three-dimensional understanding of how the atmosphere and ocean change from before the typhoon passes to after it has gone."