Comparisons of Eulerian Circulation and Circulation Budgets for Numerically Simulated Tornado-Like Vortices in Altered Shear Environments

Circulation and circulation budget calculations, in either Eulerian or Lagrangian frameworks, have been used in multi-radar and numerical modeling studies. Each framework has advantages and disadvantages. The Lagrangian framework can be used to determine the source region of important parcels that are maintaining a low-level circulation but accuracy can suffer depending upon the spatial gradients of wind velocity and choice of timestep used for trajectory calculations (Dahl et al. 2012). An Eulerian framework can monitor net changes in circulation within an analysis area and is much less computationally expensive (e.g. Trapp and Weisman 2003), however the parcel source regions cannot be investigated and it may still be sensitive to the choice of the circulation region. In this study, Eulerian circulation analyses were performed for tornado-like vortices and parent supercell mesocyclones simulated with the idealized cloud model, CM1. Starting with a long-lived simulated tornado as a control case (from Naylor and Gilmore 2012), generated from a single RUC sounding, the 0-1 km and 0-3 km shear profile was increased and decreased by 30%, 20%, and 10% while maintaining the shape of the hodograph and new simulations conducted. The altered shear profiles resulted in altered values of storm relative environmental helicity (SREH) and resulted in tornadoes of differing intensity and longevity. The Eulerian circulation analyses among all simulations were then compared to investigate the dominant terms in the circulation budget in relation to the tornado lifecycle and its associated storm environment.