Dynamical Activity Index (DAI): an integrated measure for stratospheric planetary wave activity separated by hemisphere

Total column ozone is used to trace the dynamics of the lower and middle stratosphere which is governed by planetary waves. In order to analyze planetary wave activity a Harmonic Analysis is applied to global multi-year gridded total ozone observations from three sensors (Total Ozone Monitoring Spectrometer, TOMS; Ozone Monitoring Instrument, OMI; Global Ozone Monitoring Experiment 2, GOME2). The Dynamical Activity Indices (DAIs) for planetary waves 1-3 are defined as the daily hemispheric means (0° to 50° N/S) of the amplitudes of the zonal wave numbers one, two and three, respectively.
In general, the DAIs can be regarded as a simple and robust diagnostic to quantify for example model-observation differences concerning planetary wave activity. It allows a first-guess on how the dynamics is represented in a model simulation before applying costly and more specific diagnostics. Moreover sudden stratospheric warmings can be observed and analysis of planetary wave activity is possible.