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Peer-reviewedCC BY 4.0Earth and Space Science

Clear‐Air Turbulence Upstream of a Hydraulic Jump Leading to a Helicopter Accident—A Large Eddy Simulation

  • J. Ito1,2
  • H. Niino2
  • K. Saito2,3,4
  • K. Okuyama5
5 affiliations
  1. 1Graduate School of Science Tohoku University Sendai Japan
  2. 2Atmosphere and Ocean Research Institute The University of Tokyo Kashiwa Japan
  3. 3Japan Meteorological Business Support Center Tokyo Japan
  4. 4Meteorological Research Institute Japan Meteorological Agency Tsukuba Japan
  5. 5Japan Transport Safety Board Tokyo Japan
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Abstract

This study investigates clear‐air turbulence that triggered a helicopter accident in the lee of a mountain range near Koriyama, Japan, on 1 February 2020. Using numerical weather prediction models with horizontal resolutions of 1 km and 100 m, we examined the environmental conditions and mechanisms responsible for the turbulence. The models successfully reproduced a downslope windstorm with a hydraulic jump. The finer‐resolution model (100 m), which is regarded as a large eddy simulation, revealed intense turbulence induced by Kelvin–Helmholtz instability at the boundary between the downslope wind and the overlying stagnant layer upstream of the hydraulic jump. Vertical wind speeds exceeding 10 m are associated with the turbulence at the flight level. These results highlight the importance of high‐resolution simulations for capturing hazardous clear‐air turbulence in mountainous regions.

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Cite

BibTeXRIS
BibTeX
@article{ito2026clearair,
  title = {{Clear‐Air Turbulence Upstream of a Hydraulic Jump Leading to a Helicopter Accident—A Large Eddy Simulation}},
  author = {J. Ito and H. Niino and K. Saito and K. Okuyama},
  journal = {Earth and Space Science},
  year = {2026},
  month = oct,
  doi = {10.1029/2025ea004721},
  url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EA004721},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Clear‐Air Turbulence Upstream of a Hydraulic Jump Leading to a Helicopter Accident—A Large Eddy Simulation
AU  - J. Ito
AU  - H. Niino
AU  - K. Saito
AU  - K. Okuyama
PY  - 2026
DA  - 2026/10/03
JO  - Earth and Space Science
DO  - 10.1029/2025ea004721
UR  - https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EA004721
AB  - This study investigates clear‐air turbulence that triggered a helicopter accident in the lee of a mountain range near Koriyama, Japan, on 1 February 2020. Using numerical weather prediction models with horizontal resolutions of 1 km and 100 m, we examined the environmental conditions and mechanisms responsible for the turbulence. The models successfully reproduced a downslope windstorm with a hydraulic jump. The finer‐resolution model (100 m), which is regarded as a large eddy simulation, revealed intense turbulence induced by Kelvin–Helmholtz instability at the boundary between the downslope wind and the overlying stagnant layer upstream of the hydraulic jump. Vertical wind speeds exceeding 10 m are associated with the turbulence at the flight level. These results highlight the importance of high‐resolution simulations for capturing hazardous clear‐air turbulence in mountainous regions.
SN  - 2333-5084
SN  - 2333-5084
ER  -