Solar Flare Effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis

On 28 October 2003 an extreme solar flare with significant increases in the EUV and X-ray flux caused increased photoionization effects in the dayside ionosphere and determined a remarkable solar flare effect (SFE) manifestation that preceded Halloween storm. An analysis conducted at 53 stations revealed that the geomagnetic disturbance had greatest amplitude and longest duration at lowest latitudes in the dayside hemisphere, and its characteristics were basically controlled by the zenith angle of the observing stations. The aspects of the SFE onset and initial phase reveal a close correspondence with those of the EUV flux. At equatorial/electrojet latitudes, the SFE manifestation can be mostly interpreted in terms of a significant enhancement of the preflare current system during normal electrojet conditions, with some evidence for a highly confined counter electrojet in the dawn sector. Additional elements, at higher latitudes, might suggest in these regions a more significant role of the X-ray flux and the onset of additional currents below the normal dynamo current region.