Handout (1.3 MB)
In the present study, we carried out downscale ensemble experiments with 50-m horizontal resolution. The downscale experiments produce a wide range of tornadic vortices: some members spawn strong tornadoes, and some do not have a vortex of tornado strength. Thus the results of the downscale experiments can be used to clarify the relationship between the LMC and the tornado.
To investigate the relationship between the LMC and the tornado, we produced the composite fields with the coordinate system relative to the point and time (defined by t0 min) of near-surface maximum vertical vorticity (ζmax). This composite field shows that ζ1km(t0-3) correlates to ζmax more strongly than ζ2km(t0-3) and ζ30m(t0-3), where ζzkm(t) denotes the maximum vertical vorticity at z-km height at t min. Furthermore, in the members where stronger ζmax were generated, low-level water vapor was more humid, minimum surface pressure was lower, and horizontal distance between ζ1km(t0-3) and ζ30m(t0-3) was shorter at t0-3 min. These results show that this tornado was strengthened several minutes after a strong LMC reached right above the near-surface maximum vorticity.
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