Defining a Galilean Invariant Curvature Vorticity and Its Application to the Dynamics of Vortex-Genesis in a Supercell

Vortex-genesis and growth in a supercell thunderstorm is supported by a complex
combination of inertial, buoyant and frictional forcing. Vorticity generation,
reorientation and intensification as a result of these processes can be studied using
the vorticity equation (framework). Use of this framework has led to substantial
advancements in our knowledge of how rotational flow develops at different heights
and scales within supercells. The use of the vorticity framework alone, however,
cannot explicitly distinguish vortical flow (associated with a local pressure minima)
from changes simply in vorticity magnitude. This makes it difficult to study where
and when vortices on a number of scales develop within the storm. Additionally, it
makes interpreting the responsible mechanisms for the initial forcing and
subsequent maintenance of vortex development somewhat physically unsatisfying.
Momentum divergence is another framework that can be employed to study vortex
development in supercells but that has received relatively less attention in the
literature. In this study we first analyze vortex development in the divergence
framework in an idealized sense. From this analysis, we are able to define new
diagnostic quantities including a Galilean invariant curvature vorticity that are
shown to be useful in isolating vortical flow and understanding the dynamics of
vortex growth. The development of prognostic variables is also being explored. The
framework provides a basis from which to physically interpret three-dimensional
vortex growth in a thunderstorm. Applying this theory to the analysis of numerical
storms has led to identification of key features and regions of the storm for the
development of sustained rotational flow that corroborate and extend previous
literature. Examples of its application and preliminary results will be shown at the
talk.