Structural and Environmental Characteristics of Extratropical Cyclones that Cause Tornado Outbreaks in the Warm Sector: A Composite Study

• DOI: 10.1175/mwr-d-15-0015.1
• Publication Date: 2015-12-14T22:56:03Z
• Authors: Eigo Tochimoto; Hiroshi Niino
• Keywords: Extratropical cyclone; Jet stream; Mesoscale convective system

Abstract The structural and environmental characteristics of extratropical cyclones that cause tornado outbreaks [outbreak (OCs)] do not [nonoutbreak (NOCs)] are examined using the Japanese 55-year Reanalysis dataset (JRA-55). Composite analyses show differences between OCs NOCs: for OCs, storm relative helicity (SREH) convective available potential energy (CAPE) notably larger, areas in which these parameters have significant values wider warm sector than they NOCs. larger CAPE is due to amounts low-level water vapor, while greater SREH stronger southerly wind. composite fields defined by 20-day means suggest meridional flows advect large moist air northward, creating atmospheric instability troposphere contributes occurrence a outbreak. A piecewise vorticity (PV) diagnosis shows low- midlevel PV anomalies main contributor difference winds NOCs, whereas upper-level make only minor contribution. An examination structures jet stream suggests NOCs structure stream. develop when displays anticyclonic shear. This causes more meridionally elongated resulting southeastern quadrant cyclones.