Information on the Dynamic Activity Index (DAI) based on OMI data from 2004 to
22nd, October 2017
For the calculation of the DAI, level 3 total column ozone data (gridded by 0.25 degree latitude x 0.25 degree longitude) of OMI (Ozone Monitoring Instrument) on EOS-AURA and GOME2 (Global Ozone Monitoring Experiment 2) on Metop-A as well as Metop-B are used. Due to compatibility reasons (TOMS, Total Ozone Monitoring Spectrometer is only available on a 1.0 x 1.25 degree lat-lon-grid) the data are re-gridded on a 1.0 x 1.25 degree lat-lon-grid.
Five sinusoidals with given zonal wavelengths (360°, 180°, 120°, 90°, 72°) are fitted consecutively to all data along one circle of latitude following a least-square approach (harmonic analysis). This analysis is done for each circle of latitude individually if at least 60% of all data points are available. The amplitudes of the sinusoidals are interpreted in terms of the amplitudes of the zonal quasi-stationary planetary waves one, two and three.
The DAI is calculated from the daily amplitudes of the planetary wave with zonal wave number one for the Northern and Southern hemisphere separately: all amplitudes between 0° and 50° are averaged along the corresponding hemisphere requiring 50% of data availability.