2026-01-23 京都大学
＜関連情報＞
- https://www.kyoto-u.ac.jp/ja/research-news/2026-01-23-3
- https://www.kyoto-u.ac.jp/sites/default/files/2026-01/web_2601_Ito-76df7a2050285612379698000ee6ba6f.pdf
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JD044793
北西太平洋における既存の熱帯低気圧のその後の低気圧発生への影響は限定的 Limited Influence of Pre-Existing Tropical Cyclones on Subsequent Cyclogenesis in the Western North Pacific
Kosuke Ito, Kenji Yamauchi
Journal of Geophysical Research: Atmospheres Published: 21 January 2026
DOI:https://doi.org/10.1029/2025JD044793
Abstract
Previous studies suggest that a tropical cyclone (TC) may contribute to the genesis of another TC to its east or southeast in the western North Pacific (WNP) through Rossby wave dispersion. However, the influence of a pre-existing TC (PTC) has not been fully clarified in realistic simulations. This study conducted 42 numerical experiments (NPTC) for 1981–2022, in which a PTC was removed by horizontal smoothing from the initial conditions 120 hr before the genesis of a subsequent TC (STC). Compared to control simulations with the PTC (WPTC), the number of STC formations was slightly larger (WPTC: 31, NPTC: 33). The intensities of common STCs are very similar. STCs were typically located to the south or southwest of a subtropical high. The experiments showed wave-like anomaly patterns in the vorticity field southeast of PTCs and in the geopotential height field northeast of the PTCs. Vertical wind shear (VWS), enhanced by PTC outflows, created an unfavorable environment for STC formation and intensification. Reanalysis data supported strong VWS and a similar wave-like pattern. A positive sea surface temperature anomaly over the central equatorial Pacific induced westerly wind anomalies in the southeastern WNP. The spatial collocation of PTCs and STCs was frequently observed when the active eastern convection is expected by the indices of Madden–Julian Oscillation, Boreal Summer Intraseasonal Oscillation, and El Niño–Southern Oscillation. These conditions promote TC genesis farther east, suggesting that such collocation does not imply PTC-induced formation. Thus, impact of PTCs appears less significant than previously assumed.
Plain Language Summary
This study looked at whether one tropical cyclone (TC) can help form another nearby in the western North Pacific. Using computer simulations from 1981 to 2022, it was investigated that what happens when a pre-existing TC is removed. The results show that the number of new TCs formed was almost the same, and intensity difference is limited. Instead of being triggered by nearby storms, these new TCs were more affected by large-scale weather patterns and ocean temperatures. The key message is that pre-existing TCs do not play as big a role in forming new storms as once thought—other factors are more important in driving cyclone formation in this region.
Key Points
- Pre-existing tropical cyclones have limited impact on the formation of future storms in the western North Pacific (WNP) in realistic simulations
- Vertical wind shear from earlier storms can hinder the formation of new storms nearby
- Favorable large-scale conditions, not nearby storms, better explain new cyclone formation in the WNP
