Social media posts showing Busan transformed into a "cloud city" by sea fog. [Provided by KIOST]
Social media posts showing Busan transformed into a "cloud city" by sea fog. [Provided by KIOST]

Scientists have used satellite observations to solve the "July sea fog mystery" that has drawn widespread attention along the Busan coast year after year. The recurring phenomenon has been identified as advection fog — formed when warm, humid air flows over the cold coastal waters off Busan.

The Korea Institute of Ocean Science and Technology (KIOST) announced Monday that it analyzed five years of data from the Geostationary Ocean Color Imager-II (GOCI-II) satellite from 2022 through this year, confirming that summer sea fog off Busan is not a random occurrence but advection fog that forms whenever specific oceanic and meteorological conditions align.

KIOST examined sea surface temperatures and air temperatures around Busan each year in early July. The analysis found that while the East Korea Warm Current flows through the open waters off Busan, relatively cold water forms closer to the coast. When warm, moisture-laden air rides in on southeasterly winds in early July, it cools rapidly over those cold coastal waters, causing water vapor to condense and sea fog to form.

Early July is particularly prone to the key condition for advection fog — warm, humid air passing over a cold sea — which explains why fog has been repeatedly observed around the same time in recent years.

However, the pattern has varied from year to year. In 2024, the temperature differential needed for fog formation was present, but strong winds mixed the atmosphere, preventing clear identification of sea fog in satellite imagery. In 2025, conditions favorable for fog were confined to waters immediately off Busan, producing only localized fog.

A diagram showing how advection fog forms when cold sea water meets warm air. [Provided by KIOST]
A diagram showing how advection fog forms when cold sea water meets warm air. [Provided by KIOST]

"Sea fog does not necessarily occur every July 7, but the conditions that make fog easy to form have developed almost every year around this time," said Park Myung-sook, a researcher at KIOST's Ocean Satellite Center. "As climate change rapidly alters water temperatures and ocean currents, coastal marine phenomena including sea fog may also shift, making continuous observation essential."

While sea fog creates striking scenery in urban areas, it severely limits visibility at sea and can pose serious risks to vessel navigation and maritime leisure activities. KIOST uses GOCI-II to continuously monitor waters around the Korean Peninsula, tracking the formation and movement of sea fog to support maritime safety information services.


adastra@heraldcorp.com