Response of the Magnetosphere-Ionosphere System

The disturbances of the geomagnetic field were studied from the viewpoint of their association with physical processes on the Sun and in the interplanetary space.

Both the anisotropy of ion fluxes and ion energy spectra in the magnetosheath close to the magnetopause were studied at different latitudes and for various local time sectors.
     The ACTIVE project data were used to investigate dynamics of the plasmasphere during magnetic storms (Jioieek et al. 1995).
     Data from a number of space experiment made it possible tu study energetic particle dynamics (Kuznetsov & Kudela 1995; Kuznetsov et al. 1995; Slivka 1995), fluctuations of energetic electrons at low altitudes (Kudela et al. 1997), the ion anisotropy in the magnetosheath (Kudela et al. 1998), the energetic particle acceleration mechanism (Kudela et al. 1999), their spectra (Taktakishvili et al. 1998) and to identify individual regions of the magnetospheric tail (Verkhoglyadova et al. 1999).
     Peculiarities of the electron fluxes at low altitudes were considered from the viewpoint of plausible seismic predictional type of studies (e.g. Kuznetsov & Kudela 1995; Jioieek et al. 1995).

From the viewpoint of cyclic activity of the Sun, there were revealed the features of long-term variations of occurrence of extreme conditions in the magnetosphere as well as corresponding patterns in variability of main solar wind parameters (Bieleková 1998). The morfology of annual variation geomagnetic activity was considered in terms of solar sycle phases (Bieleková 1995a; b).
     The analysis of recurrent geomagnetic variations revealed dynamics of spectral structure within this frequency range, its relation to the solar wind and interplanetary magnetic field parameters and the peculiarities of reccurency for odd and even cycles (e.g. Prigancová et al. 1995).
     Solar wind parameters are of a decisive role in energization of magnetospheric processes. This approach was especially applied in case of magnetic storms. Prigancová (1995) has shown that the accuracy of reconstruction of the ring current (RC) magnetic field profiles is recently improved. The adequate description of the RC energization implies the proper option of both the decay parameter t and energy injection rate given by current solar wind parameters. The results obtained were also presented at the meetings (e.g. Prigancová 1996, 1997).
     The study of diversity of the geomagnetosphere response and its modeling was pointed at peculiarities of interaction processes in the Sun-Earth system, their identification, verification and interpretation being emphasized. There was revealed the magnetospheric heterogeneity during stormy periods which is associated with nonlinearities of induced processes (Prigancová 1996).

The investigation of the non-linear character of the magnetospheric response was started. The ring current magnetic field fluctuations were analysed as an instability scaling of initially exponential-growing process (Vörös 1995b).
     Stochastic reconnection was considered by means of a percolation model (Vörös 1995a). Some results on magnetospheric response as a non-linear process were presented at international meetings and conferences (e.g. Green et al. 1997, Körmendi et al. 1997; Vörös 1997; Vörös et al. 1997a, b, c, and Vörös 1998). The application of geophysical methods in the analysis of meteorological disasters was also reported (Valach & Vörös 1998).
     The multifractal formalism is recently applied for geophysical fields (Davis et al. 1994). Vörös (1996) has used the multifractal techniques and a self-organized criticality (SOC) approach as a unifying concept describing the dynamics of open non-linear systems which evolve towards a critical state charecterized by response functions obeying power-laws and self-affine geometry. Since the magnetosphere acts as a SOC system exhibiting globally coherent behaviour the approach for the synthesis of planetary indices of geomagnetic activity has been applied (Vörös 1996a, b, and Vörös 1998).
     This approach has been also applied to study solar activity periodicities (Dorotovie & Vörös 1996, 1997) and to investigate the earth's fluid core motions (Vörös & Gianibelli 1998; see also Section "Theories of geomagnetic field generation" in this IAGA Report).

The study of the magnetosphere as a non-linear dynamical system made it possible to specify plasma instabilities and to carry out their multifractal analysis. The mean scale exponent value q_p= 2.5± 0.2, calculated by means of power-law statistics is characteristic of quite a numerous manifestations of magnetospheric and auroral activity. Self-organisation of the magnetosphere during the development of disturbances was revealed. The identity of scaling relations for both non-linear MHD turbulences in solar wind and for low-frequency fluctuations in the magnetosphere was stated. Experimental study of the intermittent energy transfer has allowed to reveal and generalize the scale invariance feature of these processes and to explain the diversity of magnetosphere fluctuations by an universal clue of structural dynamics (Vörös et al. 1997 and Vörös et al. 1998).
     The problems of ionospheric physics have been also studied.Some properties of the lower ionosphere and middle atmosphere were reported from the viewpoint of chemical composition and its dynamics withregard to solar activity (Ondrášková 1995).Model calculations have shown that an increase in O concentrationcauses a similar increase in electron concentration under 70 km (Ondrášková 1995, 1997). Using a simple model of lower ionosphere model reflection heights of 162 kHz radio waves were computed and compared with experimental heights. Model-experiment differences in seasonal variation of this height can be explained only by seasonal variation of minor components, predominantly of NO. The maxima of reflection height occurring in equinoxes are likely to reflect the global change in atmospheric circulation during which the transport of NO from above downward is interrupted (Ondrášková 1998).
     A succesful attempt to detect the Schumann resonance peaks in the 5-30 Hz spectral band of the Earth's magnetic field horizontal component was made. The measurements were carried out by the three-axis superconductive SQUID magnetometer. During several short experimental sessions, the first three Schumann resonance peaks were clearly distinguished and detected (Siráň, Ondrášková, Turoa, Kostecký & Janu 1999).
     The analysis of the air temperature time series 1871-1995 covering solar cycles from 12 up to 22 revealed the oscillatory character of the long-term dynamics of the smoothed temperature anomaly field profiles. There are successive warmings and coolings on time scales of about 3– 5-yr, 22-yr and 70– 80-yr rhythmicity. The association with solar forcing is likely to be relevant (Prigancová 1997 and Prigancová et al. 1998).

The main results on STP activities are summarized in brief by Prigancová & Sýkora (1995/1996). The information on highlights of solar terrestrial studies can be also found in (Prigancová 1998).