Application of GPS-derived total electron content maps to derivation of planetary ionosphere storm index

The GPS-derived global ionospheric maps (GIM) of the vertical total electron content, TEC, are used for derivation of planetary index of the ionospheric perturbations. TEC grids given in geographic frame of latitudes from 87.5°S to 87.5°N in step of 2.5° and longitudes 180°W to 180°E with a step of 5° are converted to magnetic latitude MLAT versus magnetic local time frame for 0 to 23 hrs MLT with a step of 1h during 1999-2009. The index of ionosphere activity, W-index, is generated with relevant thresholds equal to 1 or -1 for the quiet state, 2 or -2 for the moderate disturbance, 3 or -3 for the moderate ionospheric storm, and 4 or -4 for the intense ionospheric storm at each grid point of the MLAT-MLT map. Then the planetary differential Wp index is obtained from W index map as MLAT average of ranges between maximum positive and minimum negative index weighted by the extent of the extreme values on the map. In total, more than 140 planetary ionospheric storms have been detected with Wp index for 1999-2009. Storms identified that way are compared with the magnetospheric storms specified by Dst, AE and Ap indices. The planetary Wp index discloses the storms which may belong either to magnetosphere, the ionosphereplasmasphere system or both, providing broader proxy index driving the space weather than the geomagnetic indices alone.