Vortex Developments and Interactions in Idealized Supercell Simulations Investigated By the Kinematic Vorticity Number Wk

The hook echo region of a supercell rapidly changes in time. The appearance of the hock echo region seems to be determined by the complex interplay of rotational flow and shearing motions. Vortex developments and interactions of vortex structures in the vicinity of the updraft could be a further reason for the temporal evolution of the hook echo. In this work we will take a closer look on this region by analyzing the kinematic flow properties with help of the kinematic vorticity number. The kinematic vorticity number Wk is defined as the ratio of local rotation rate and strain rate. Hence, Wk allows for the diagnostic identification of vortices in three-dimensional flow fields. Based on Wk a vortex is identified as simply-connected region of prevailing rotation rate, i.e. Wk > 1, and the vortex core boundary is given by Wk = 1 which represents a pure shearing motion and a balance of rotation rate and strain rate. The incompressible, inviscid, barotropic vorticity equation can be rewritten in a non-dimensional way using the kinematic vorticity number. Under these conditions the equation indicates that effective vorticity developments occur in regions of Wk approximately 1. Hence, this work will further focus on the analysis of Wk fields in idealized supercell simulations regarding the connection between regions of Wk approximately 1 and the structure, distribution and growth rate of vortex developments.