環境：海流を調べると熱帯低気圧の勢力が強くなっていることが分かった

Weak tropical cyclones, which account for 70% of tropical cyclones, have been strengthening across all ocean basins over the past three decades as a result of ocean warming, according to a study in Nature this week.

Tropical cyclones can devastate coastal communities when they make landfall, so to be prepared for their impacts, it is crucial to understand how they work. Theoretical and mathematical models agree that tropical cyclones should strengthen as sea surface temperatures increase, yet this is debated due to a lack of sufficiently accurate satellite-based observational evidence. Conventional satellite-based evidence may be contaminated by heavy rain, clouds, breaking waves, and spray.

Guihua Wang and colleagues use a unique set of ocean current observations — high-quality current measurements by floating devices called surface drifters — to quantify tropical cyclone intensity in a new way that complements traditional methods. A close relationship exists between tropical cyclones and ocean currents, and drifters deployed by the National Oceanic and Atmospheric Administration provide highly accurate current measurements. The authors’ analysis shows that weak tropical cyclones, classified as tropical storms and category-1 tropical cyclones, have been intensifying from 1991 to 2020 as a result of global warming.

These results provide a baseline that can be used to assess tropical cyclone model simulations and projections, helping to make their predictions more accurate.