The warm-core structure of typhoons as observed throughthe T-PARCII aircraft reconnaissance and upper-air soundings
Hiroyuki Yamada1,8, Kosuke Ito1,8, Soichiro Hirano1, Kazuhisa Tsuboki2,8,Taro Shinoda2, Masaya Kato2, Sachie Kanada2, Tadayasu Ohigashi3, Satoki Tsujino,
4, Udai Shimada4,8, Tetsuo Nakazawa4, Norio Nagahama5, Kensaku Shimizu5,
Takeshi Horinouchi6,8, Nobuhiro Takahashi2, Shingo Shimizu3, Masashi Minamide7
1 University of the Ryukyus, 2 Nagoya University, 3 National Research Institute for Earth Scienceand Disaster Resilience, 4 Meteorological Research Institute, Japan Meteorological Agency,
5Meisei Electric Co. Ltd., 6 Hokkaido University, 7 University of Tokyo,
8Typhoon Science and Technology Research Center, Yokohama National University
ABSTRACT

Upper-tropospheric reconnaissance flights were carried out using a civil jet with a dropsonde
system for three intense typhoons: Lan in 2017 (Yamada et al. 2021; Tsujino et al. 2021; Ito et al.
2018), Trami in 2018 (Hirano et al. 2021), and Mindulle in 2021. In all flights, we succeeded tofly into the eye and to deploy dropsondes near the circulation center. In addition, the eye of two
tropical cyclones (Ampil and Trami in 2018) were observed using radiosondes launched fromstations in the Ryukyu islands. These in-situ observations provide opportunities to examine thevertical structure of the warm core in a very fine resolution (10~15 meters) between the Earthsurface and the upper troposphere (~13 km MSL). They also provide opportunities to clarify arelationship between the warmth of the circulation center and the typhoon intensity in a direct way,
which will be helpful for improving intensity estimation using a satellite-based microwave
temperature sounder. In this work, we examined the warm-core structure of these typhoons andthe relationship between the warm core and the typhoon intensity. In each sounding, thetemperature anomaly of the warm core was defined as the difference in temperatures between theeye and the surrounding region (radius of 550-600 km). The mean temperature anomaly between
900 and 250 hPa was calculated and was plotted as a function of the sea-level pressure, whichshows a robust strong positive relationship between strength of the warm core and typhoonintensity, as should be expected for a balanced vortex. However, comparing some observations of
Mindulle and Lan, the temperature anomalies are almost the same (8-10 K) even though the sealevel pressures differ by about 10 hPa. This suggests not only hydrostatic equilibrium, but also
other factors involved in the determination of the minimum sea-level pressure of a typhoon. These
results suggest that to clarify a cause of the fluctuation of warm-core strength will contribute to animprovement of typhoon intensity estimation using a satellite microwave sounder.
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Keywords: tropical cyclone intensity, warm-core structure, aircraft reconnaissance