Forcing Mechanisms for Internal Rear-Flank Downdraft Surges

Internal RFD surges are hypothesized to be related to tornadogenesis, tornado maintenance, and tornado dissipation.  In this work, an internal RFD surge is generated within a idealized simulation of a supercell.  Similarly to observations, the surge wraps cyclonically around an intensifying low-level mesocyclone and exhibits a distinct vorticity maxima to the left of its apex, which eventually merges into the primary mesocyclone.  Agglomerative cluster analysis is applied to parcel trajectories in order to define coherent airstreams within the surge and momentum budgets are constructed for each airstream in order to determine the forcing mechanisms for the surge.