Extreme solar events and magnetic storms in October 2003 and...

4. Conclusions

[42] The analysis of the variations of VLF signal parameters at midlatitude paths made it possible to complete the picture of development of auroral processes at middle latitudes during the extreme magnetic storms on 29-30 October 2003 following prominent solar flares on 28 and 29 October 2003.

[43] The analysis of VLF signals showed that at middle latitudes in the daytime strong variations of the signal phases occurred and was related to the X-ray radiation from the solar flares.

[44] Model calculations of the electron concentration in the midlatitude ionosphere D layer after solar flares gave an increase in N_e after solar flares by a factor of 20 and lowering of the ionosphere down to its daytime position during the magnetic storms in the nighttime and morning hours on 29 and 30 October. The latter fact indicates that there occurred an injection into the ionosphere of electrons with energies of hundreds keV.

[45] The obtained results provide an experimental confirmation of the shift of the auroral processes down to geomagnetic latitudes of 40-45^o N in some periods of time on 29-30 October 2003.

[46] The joint analysis of the data on VLF signals, structure and dynamics of the magnetosphere, and also auroral and magnetic activity shows that in the evening UT hours on 29 and 30 October 2003 there occurred a splitting of the auroral processes region to two zones separated in latitude. One of the zones was located at geomagnetic latitudes > 50-55^o N and the second zone was located at latitudes of 40-45^o N. The splitting of the auroral zone was accompanied by intense development of the Dst variations.

[47] On 29-30 October 2003 four intervals were registered when the Kp index reached 9 at 0900-1200 UT and 2100-2400 UT on 29 October and 0300 UT and 2100-2400 UT on 30 October. Within these intervals in each case there were its own peculiarities in development of auroral processes (energetic electron injection) in the ionosphere region. On 29 October at 0900-1200 UT no auroral processes developed at latitudes of 40-45^o N, at 2100-2400 UT the auroral processes developed at these latitudes only in the dawn sector of the magnetosphere, whereas on 30 October at 2100-2400 UT the auroral processes at geomagnetic latitudes of 40-45^o N covered the region from the dusk to the dawn parts of the magnetosphere.