In summary, tornadogenesis occurs in concert with a complex process of cyclonic vertical vorticity accumulation at an inflection point that develops along the FFDB. The timing and location of tornadogenesis also appear associated with the intensification and location of abrupt tilting of the SVC.
The position of the tornado with respect to the SVC remains largely unchanged and the VVS with attendant rearward-moving vortices continues to provide vertical vorticity to the tornado along the storm's FFDB (Fig.
The VVS during this extended intensification period has become very active with a markedly increased accumulation of vertical vorticity along the FFDB. Cyclonic vertical vorticity continues to be absorbed into the tornado as vorticity is extruded from like-signed vortices and vorticity patches moving into it (e.g., Coreos and Sherman 1984; McWilliams 1984; Lee and Wilhelmson 1997).
A lobe of low pressure extending along and behind the FFDB is also readily apparent in the pressure field.
By t = 9,120 s, the vorticity magnitude present in the SVC has decreased, as indicated by the increased transparency of the volume-rendered vorticity field, and fewer cyclonic misocyclonic vortices are present along the FFDB. Further, the tornado has become increasingly surrounded by horizontal and vertical vortices originating from the rear flank that have been cyclonically advected around the periphery of the tornado.
Figure 16 shows the volume-rendered cloud water mixing ratio field and surface potential temperature perturbation ([theta]') field looking down the storm's FFDB toward the end of the maintenance phase.
The intensification of the low-level updraft occurred roughly coincident with the development and intensification of a "current" of streamwise vorticity (the SVC) originating along the FFDB that was tilted into the storms updraft.
Many of the features described in the genesis phase of the storm are maintained through much of the maintenance stage, including the flow of cyclonic vertical vorticity along the FFDB that was absorbed into the tornado, the SVC and SVC-relative position of the tornado that became more optimally aligned under and within the strong deep updraft, and the ingestion of streamwise vorticity along and behind the storm's forward-flank downdraft boundary.