In this study, the evolution of vortex lines within low-level mesocyclones and tornadoes is examined in order to confirm the above mentioned conclusions by comparing it to the recent observational studies. As a result, a low-level mesocyclone contains a lot of vortex lines originating from environmental streamwise voriticy. After the development of the low-level mesocyclone, vortex lines having environmental streamwise vorticity wrap around the low-level mesocyclone, and a secondary RFD surge depresses the vortex lines downward in a nearly barotropical manner, which leads to tornadogenesis.
Meanwhile, as to F3 Supercell tornado, which hit Tsukuba City in Japan on 6 May 2012, vortex lines emanating from the low-level mesocyclone form the arches straddling the hook-shaped hydrometers distribution. This result indicates that baroclinic vorticity generation within RFD region is effective for a low-level mesocyclone formation as in the recent observational studies of suprecells in midwestern United States.
Thus, mechanisms of supercell tornadogenesis vary depending on the environmental conditions.