Global Warming Likely to Expand Radius of Gale Force Wind of Tropical Cyclones

Image by photo-graphe.

The Japan Agency for Marine-Earth Science and Technology and the University of Tokyo jointly announced on September 14, 2017, the results of an analysis of changes in tropical cyclone activity and structure associated with global warming. The joint group conducted the analysis by running a program called NICAM, or Nonhydrostatic Icosahedral Atmospheric Model, on the K supercomputer; NICAM is capable of calculating the formation and vanishing processes of clouds globally. Comparing the distribution of wind speeds around tropical cyclones, the analysts found that, under warmer climate conditions, the radius of gale force wind will expand for cyclones of the same intensity categories.

The analysis compared historical data covering 60 years (1979 to 2008) with the results of a simulation of future climate around the end of the 21st century (2075 to 2104). The results showed that, globally on average, the number of tropical cyclones will decrease by 22.7 percent (%), the number of strong tropical cyclones will increase by 6.6%, and rainfall levels accompanied by tropical cyclones will increase by 11.8%. The radius of gale force wind will increase by 10.9% under warmer climate conditions.

Global atmospheric calculation models previously used for climate predictions had a low horizontal resolution, of tens to hundreds of kilometers, compared to the present analysis, which had a horizontal definition of 14 kilometers. Predictions have been unreliable because cloud systems were explained based on assumptions derived from past experience. The research group succeeded in eliminating uncertainty by using high-resolution NICAM and collecting data on the changes in tropical cyclone scale and on cyclone mechanisms. The group now hopes to further eliminate uncertainty by achieving higher resolutions and deepening their understanding of changes in tropical cyclone activity.