Study on a Typhoon-Induced Gravity Wave Captured by High-Altitude Radiosonde Observations in Okinawa in July 2024

Understanding the characteristics of atmospheric gravity waves driving stratospheric circulation, which directly influence tropospheric weather, is of considerable importance. However, in-situ observation datasets in the middle and upper stratosphere remain limited. To investigate gravity wave activity in this part of the atmosphere, we conducted high-altitude radiosonde observations using large rubber balloons over Okinawa, Japan, in July 2024, obtaining wind velocity and temperature data. During the observation, a distinctive fluctuation was observed on July 25 as Typhoon Gaemi passed southwest of Okinawa. In this study, we investigate the characteristics of the observed fluctuation using hodograph and ray tracing analyses. The results suggest that the fluctuation was a gravity wave with a large vertical wavelength ~ 11 km, originating near the center of Typhoon Gaemi and propagating upward and east-northeast direction. Furthermore, the typhoon-induced gravity waves were modulated by the easterly mean wind field, suggesting that their vertical propagation characteristics differed between the eastern and western sectors of the typhoon.