COST Action 724 "Developing the basis for monitoring, modelling and predicting Space Weather", Sofia, Bulgaria, May 2007 Atmospheric emissions and shortperiod geomagnetic pulsations during superstorms of the second millenium Malozemova Yu1., Mikhalev A.2, Mishin V.2, Stoeva P.3, Tsegmed B.2 1 Irkutsk State Agriculture Academy 2 Insnitute of Solar - Terrestrial Physics RAS, Irkutsk, Russia 3 STIL-BAS `Acad. D. Mishev` Stara Zagora, Bulgaria

Abstract  The regime of geomagnetic pulsations associated with middle- latitude optical emissions during superstorms on 6 April 2000 and 20 November 2003 is considered. Emissions are observed in Irkutsk (52°N, 103°E) by Mikhalev et al., 2004 and visually in Sofia, Bulgaria (43°N, 25°E) by P. Stoeva (private communication).  Amplitude of the Pc1 geomagnetic pulsations observed in Irkutsk on 20 November 2003 at ~2000 UT was extremely large - A~0.35 nT. Intensity of the red oxygen airglow emission O(1D) 6300Å was also recorded at Irkutsk (I=19.4 KR). During this superstorm, the value of Dst was -472 nT, magnetosphere was extremely compressed and the inner edge of ion plasma sheet reached as deep as at L=1.5 at 19:00UT.  Decrease of the H-component of magnetic field at Irkutsk was 400 nТ and reached the minimal value in 19:40 UT. In some minutes the peak of lights in the red oxygen line O(1D) 6300Å was observed, and peaks of the green oxygen line O(1S) 5577Å and the dark blue line (3600 – 4100 Å) were observed a little bit earlier.

Abstract…  Pulsations Рс1 were continuously observed after 18:30 UT up to 20:40 UT, but during the maximum of the optical emission the amplitude of the Pc1 pulsations sharply decreased. We assume, that the strong particle precipitation stipulated not only optical glow, but also two reasons of observed impairment of pulsations. At first, change of pitch-angle distribution of trapped protons at their precipitation should cause decrease of cyclotron instability of protons near the equator, that is decrease of the generation mechanism of pulsations. Besides, the strong precipitation of charged particles into ionosphere could call deterioration of a wave guide for hydromagnetic waves over the Pc1 range and decrease of coefficient of their penetration to ionosphere.  It is interesting to note the coincidence of Рс1 period and the period of wave structure of particle convection velocity in the area of ionospheric troughs (E.V. Mishin et al., 2004) during a superstorm on April 6, This coincidence speaks about possible display of instability of protons of plasma sheet (ring current) both in generation of the Pc1 pulsations, and in their dynamics in ionosphere.

I, Rayleigh Figure I - intensity of the optical emissions in Rayleihg, in the red O(1D) 6300Å and green O(1S) 5577Å oxygen lines. The shorter wave emissions (dark blue, Å) have smaller intensity and are synchronous with the green line (here are not shown). Components of the geomagnetic field in Irkutsk: D magnetic declination in min (blue curve) and Н horizontal component of the magnetic field (black curve) Fluxes of trapped energetic protons (black curve) and electrons (violet curve) according to LANL-4 satellite in pre-midnight sector outside the plasmapause. Dynamic spectra of geomagnetic pulsations in Irkutsk in the range of the periods from 0.5 sec up to 60 sec (from top to down). Dst - variation of geomagnetic field.

November 20, 2003 Superstorm  It is one of the strongest geomagnetic storms in history. After jumps of the solar wind density the plasma sheet density increased from n=2 cm-3 to n=5 cm-3 at 18:10 UT and 20:10 UT and the ring current became very strong: Dst=-472 nt. The inner edge of the ion plasma sheet gradually moved inwards during the main phase and reached as deep as L=1.5 at about 19:00UT.  Equatorward edge of the field aligned currents moves towards the equartor to 400 N MLAT at 14:00 UT (Ebihara et al, 2005).  During the main phase of this superstorm in Irkutsk amplitude of the Pc1 geomagnetic pulsations was extremely large: A~0.35 nT. Intensity of the red oxygen airglow emission O(1D) 6300Å was also the largest for all events recorded in Irkutsk (I=19.4 KR).

 Decrease of the H-component of magnetic field at Irkutsk was 400 nТ and reached the minimal value in 19:40 UT. In some minutes the peak of lights in the red oxygen line O(1D) 6300Å was observed, and the peak of the green oxygen line O(1S) 5577Å and the dark blue (3600 – 4100 Å) lines was observed a little bit earlier. Pulsations Рс1 were observed continuously after 18:30 up to 20:40 UT, but during the maximal optical emission the amplitude of the Pc1 pulsations greatly decreased.  We associate the mechanism of the Pc1 pulsations generation with the ion-cyclotron instability of energetic protons of the geocorona. The flux of energetic protons increases during the time interval of pulsations’ intensification. November 20, 2003 Superstorm…

 We assume, that the strong particle precipitation stipulated not only optical glow, but also two reasons of observed impairment of pulsations. At first, the change of pitch-angle distribution of trapped protons at their precipitation should cause decrease of cyclotron instability of protons near the equator, that is decrease of the generation mechanism of pulsations. Besides, the strong precipitation of charged particles into ionosphere could call deterioration of a wave guide for hydromagnetic waves over the Pc1 range and decrease of coefficient of their penetration into ionosphere.  It is interesting to note coincidence of the Рс1 period to the period of wave structure of particle convection velocity in the area of ionospheric troughs (E.V. Mishin et al., 2004) during the superstorm on April 6, This coincidence speaks about possible display of instability of protons of plasma sheet (ring current) both in generation of the Pc1 pulsations, and in their dynamics in ionosphere. November 20, 2003 Superstorm…

 This work was partly supported by RFBR research grant N  References:  A.V. Mikhalev, A. V. Beletsky, N.V. Kostyleva, and M.A. Chernigovskaya. Midlatitude auroras at the Eastern Siberia during strong geomagnetic storms on October 29-3, and November 20-21, 2003, Kosmicheskie issledovaniya, V.42, N6, pp , 2004 (in Russian).  Y. Ebihara, M.-C. Fok, S. Sazykin, M. F. Thomsen, M. R. Hairston, D. S. Evans, F. J. Rich, and M. Ejiri. Ring current and the magnetosphere-ionosphere coupling during the superstorm of 20 November J. GEOPHYS. RES., V. 110, A09S22, doi: /2004JA010924, 2005  E.V. Mishin, W.J. Burke and A.A. Viggiano. Stormtime subauroral density troughs: Ion-molecular kinetic effects. J. Geophys. Res. V. 109, A10301, doi: /2004JA010438, November 20, 2003 Superstorm…