МЕЖДУНАРОДНАЯ КОНФЕРЕНЦИЯ «Перспективные материалы с иерархической структурой для

The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.

The relation of the maximal daily average values of the relativistic electron fluxes with an energy higher than 2 MeV, obtained from the measurements on GOES geostationary satellites, during the recovery phase of magnetic storms to the solar wind parameters and magnetospheric activity indices has been considered. The parameters of Pc5 and Pi1 geomagnetic pulsations and the relativistic electron fluxes during the prestorm period and the main phase of magnetic storms have been used together with the traditional indices of geomagnetic activity (A E, K p, D st). A simple model for predicting relativistic electron fluxes has been proposed for the first three days of the magnetic storm recovery phase. The predicted fluxes of the outer radiation belt relativistic electrons well correlate with the observed values (R ∼ 0.8–0.9).

It is well known that during many but not all of the geomagnetic storms enhanced fluxes of high-energy electrons are observed in the outer radiation belt. Here we examine relativistic (>2MeV) electron fluxes measured by GOES at the synchronous orbit and on-ground observations of two types of ULF pulsations during 30 magnetic storms occurred during 1996–2000. To characterize the effectiveness of the chosen magnetic storms in producing relativistic electron fluxes, following to (Reeves, G.D., McAdams, K.L., Friedel, R.H.W., O’Brien, T.R. Acceleration and loss of relativistic electrons during geomagnetic storms. Geophys. Res. Lett. 30, doi:10.1029/2002GL016513, 2003), we calculate a ratio of the maximum daily-averaged electron flux measured during the recovery phase, to the mean pre-storm electron flux. A storm is considered an effective one if its ratio exceeds 2. We compare behavior of Pi1 and Pc5 geomagnetic pulsations during effective and non-effective storms and find a tendency for a storm efficiency to be higher when the mid-latitude Pi1 pulsations are observed for a long time during the magnetic storm main phase. We note also that the prolonged powerful Pc5 pulsation activity during the recovery phase of a magnetic storm is the necessary condition for the storm effectiveness. To interpret the found dependences, we suggest that there are two prerequisites for generating relativistic electron populations during a storm: (1) the availability of seed electrons in the magnetosphere, and Pi1 emissions are indicators of the mid-energy electron interaction with the ionosphere and (2) acceleration of the seed electrons to MeV energies, and interaction of electrons with the MHD wave activity in the Pc5 range is one of the most probable mechanisms proposed in the literature for this purpose.

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT andlast more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1, 2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

Midlatitude geomagnetic pulsations in the Pc1,2 frequency range (0.1-2 Hz), whose intensity is evidently controlled by variations in the solar wind dynamic pressure (P-SW), are presented. The considered wave phenomena have been recorded at two midlatitude observatories at a maximum and at the early stage of recovery of seven magnetic storms. It has been indicated that pulsations modulated by P-SW variations are observed at midlatitudes even in the cases when dynamic pressure changes behind the solar wind region with a quasistationary negative IMF B-z component, which interacts with the Earth's magnetosphere for 4 h and more. Pulsations with diminishing period (IPDP), registered during two considered storms, also accompany or follow increased P-SW. However, the growth of pulsation amplitudes during these events is related to both increase and decrease in the pressure.

The space-time evolution of the region of reduced total electron content (TEC) during the large magnetic storm of April 6-7, 2000, has been investigated on the basis of data from the IRKT midlatitude station (geographic coordinates 52.22degrees N and 104.32degrees E) for receiving radiosignals from the GSP (Global Positionin System) satellites. The region of TEC depletion was for a long time (during 9 h) within the IRKT reception zone and slowly drifted equatorward. It has been demonstrated that the variations in the spectral-polarization characteristics of pulsations, recorded at the Earth's surface below the region of TEC depletion correspond to the concept of a successive passage of the plasmapause, ring current, and the region of diffuse precipitations of the plasma sheet particles over the observatory. It has been concluded that, in the considered event, the region of TEC depletion is an attribute of the main ionospheric trough (MIT) displaced toward midlatitudes under the conditions of enhanced magnetospheric convection.

Variations in the critical frequency and height of the ionospheric F2 layer maximum, accompanying midlatitude geomagnetic pulsations of the IPDP type, are studied statistically. The main attention is paid to the analysis of the data of the Irkutsk midlatitude ionospheric station located in the region of the oscillation registration. It is shown that IPDP are mainly observed against a background of positive disturbances of the critical frequency and height of the midlatitude F2 region, equally probable appearance of positive and negative F2-layer disturbances. and intense ionospheric disturbances over the observatories located about similar to10degrees and 18degrees northward from Irkutsk. respectively. A tendency of the IPDP initial periods toward increasing with an increase of foF2 and the F2-layer half-thickness in Irkutsk is found.

A comparative analysis of the spectra of Pi 1 geomagnetic pulsations, simultaneously recorded at the high-latitude observatory Noril'sk and midlatitude observatory Irkutsk, has been performed. It has been shown that the difference in the periods between the Pi 1 spectral maxima in Noril'sk and Irkutsk depends on the critical frequencies of the Ionospheric F2 layer along the signal propagation path. Tendencies have been uncovered toward decrease and increase in the midlatitude oscillation periods with increasing foF2 in the nightside and dayside sectors, respectively, which can be caused by the diurnal variation in the ionospheric thickness. A method for deriving relative changes in the ionospheric F2 layer thickness from Pi 1 periods has been proposed.

During an interaction of the Earth’s magnetosphere with the interplanetary magnetic cloud on October 18–19, 1995, a great magnetic storm took place. Extremely intense disturbances of the geomagnetic field and ionosphere were recorded at the midlatitude observatory at Irkutsk (Φ′≈45°, Λ′≈177°, L≈2) in the course of the storm. The most important storm features in the ionosphere and magnetic field are: a significant decrease in the geomagnetic field Z component during the storm main phase; unusually large amplitudes of geomagnetic pulsations in the Pi1 frequency band; extremely low values of critical frequencies of the ionospheric F2-layer; an appearance of intense Es-layers similar to auroral sporadic layers at the end of the recovery phase. These magnetic storm manifestations are typical for auroral and subauroral latitudes but are extremely rare in middle latitudes. We analyze the storm-time midlatitude phenomena and attempt to explore the magnetospheric storm processes using the data of ground observations of geomagnetic pulsations. It is concluded that the dominant mechanism responsible for the development of the October 18–19, 1995 storm is the quasi-stationary transport of plasma sheet particles up to L≈2 shells rather than multiple substorm injections of plasma clouds into the inner magnetosphere.