A Study of Constant Absolute Vorticity Trajectories on Isentropic Surfaces

Abstract

It is shown that constant absolute vorticity (CAV) trajectories are more useful on isentropic surfaces than on constant pressure surfaces. A form of the vorticity equation is derived by use of Lagrangian methods. This form is similar to the Rossby form, and ordinary methods of computing CAV trajectories can be used with isentropic charts. A series of isentropic streamline charts were prepared and CAV trajectories were constructed at certain points on these charts. CAV trajectories were also constructed on 500-mb charts for the same time. 24- and 48-hr forecasts of wind direction and speed were made from CAV trajectories on both sets of charts, and verified. The results of these forecasts are treated statistically, and forecasts from CAV trajectories on isentropic charts are shown to be significantly better than similar forecasts from 500-mb charts. The effects of the divergence term of the vorticity equation are discussed qualitatively.