4.4 Article

Tornadogenesis in a Quasi-Linear Convective System over Kanto Plain in Japan: A Numerical Case Study

期刊

MONTHLY WEATHER REVIEW
卷 150, 期 1, 页码 259-282

出版社

AMER METEOROLOGICAL SOC
DOI: 10.1175/MWR-D-20-0402.1

关键词

Convective storms/systems; Extratropical cyclones; Tornadogenesis; Tornadoes; Convective storms

资金

  1. Ministry of Education, Culture, Sports, and Technology [hp160229, hp170246, hp180194, hp190156]
  2. MEXT [hp200128, hp210166]
  3. Public/Private R&D Investment Strategic Expansion PrograM (PRISM)
  4. JSPS KAKENHI [24244074, 18H01277]
  5. Atmosphere and Ocean Research Institute, The University of Tokyo [159]
  6. Grants-in-Aid for Scientific Research [18H01277] Funding Source: KAKEN

向作者/读者索取更多资源

The environmental characteristics and formation process of a tornado spawned by a quasi-linear convective system (QLCS) over Kanto Plain, Japan, were examined using observations, a reanalysis dataset, and a high-resolution numerical simulation. The study found that the formation of the tornado was associated with a low-level jet, pressure gradient, and rear inflow jet in the QLCS environment. Additionally, crosswise vorticity in the forward inflow region of the QLCS played a significant role in the formation of the tornado.
The environmental characteristics and formation process of a tornado spawned by a quasi-linear convective system (QLCS) over Kanto Plain, Japan, are examined using observations, a reanalysis dataset, and a high-resolution numerical simulation with a horizontal grid spacing of 50 m. The QLCS environment responsible for tornadogenesis was characterized by small convective available potential energy and large storm-relative environmental helicity due to strong vertical shear associated with a low-level jet. The strong low-level jet was associated with a large zonal pressure gradient between two meridionally aligned extratropical cyclones and a synoptic-scale high pressure system to the east. The numerical simulation reproduced the tornado in the central part of the QLCS. Before the tornadogenesis, three mesovortices developed that were meridionally aligned at 500-m height, and a rear inflow jet (RIJ) associated with relatively cold air originated from aloft and developed on the west side of the QLCS, while descending from rear to front. Tornadogenesis occurred in the southernmost mesovortex at the northern tip of the RIJ. This mesovortex induces strong low-level updrafts through vertical pressure gradient force. A circulation analysis and vorticity budget analysis for the mesovortex show that environmental crosswise vorticity in the forward inflow region east of the QLCS played a significant role in the formation of the mesovortex. The circulation analysis for the tornado shows that frictional effects contribute to the increase of circulation associated with the tornado. Moreover, environmental shear associated with horizontal and vertical shear of the horizontal wind also contribute to the circulation of the tornado.

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