  The Dynamic State Index is a scalar quantity designed to identify atmospheric
developments such as fronts, hurricanes or specific weather pattern. The DSI is
defined as Jacobian-determinant of three constitutive quantities that
characterize three-dimensional fluid flows: the Bernoulli stream function, the
potential vorticity (PV) and the potential temperature. Here, we tackle the
questions (i) if the mathematical formulation of the DSI can be reduced, while
keeping the main information, and (ii) does the reduction of the DSI depend on
the spatial scale? Applying principle component analysis we find that three of
six DSI terms that sum up to the Jacobi-determinant are sufficient for future
DSI calculations.
