The Space Research Institute has scientific departments and laboratories studying various aspects of cosmophysics: space plasma, planets, experimental and theoretical astrophysics, optical and physical studies.

Experimental and theoretical investigations concerning a number of aspects of solar - terrestrial connections as well as magnetospheric physics were carried out. The main scientific results have been obtained in a frame of the International Project INTERBALL.

Theoretical study of the plasma structure formation and its evolution in the collisionless space plasma under the influence of stochastic as well as quasilinear diffusion with a proper model of magnetotail magnetic field lets us to describe the quasi-interference structure of plasma distribution in the Earth's magnetotail. The magnetotail formation from a plasma mantle source was investigated in the presence of model dawn-dusk electric field. It was shown that the energization and the scattering of plasma particles resulting from chaotic acceleration in the magnetic field reversal region leads to the formation of the ion distributions with velocity space holes in the central plasma sheet and to the formation of fine-structured fast ion eams (so-called beamlets) with a velocity space distribution resembles a "keadney bean" in the plasma sheet boundary layer. The results of our study gave also an explanation for a large pitch-angle cut off in beamlet ion distributions often observed by INTERBALL.

The analytical investigation have shown that an existence of velocity space holes in the plasma sheet ion distributions leads to generation of very low-frequency electrostatic waves with wave vectors located in a narrow angle region around Sun-Earth line. Excited waves changed the form of the initial hole due to velocity space trapping of low-energy background ions. Thus an ion velocity distribution existing in the central plasma sheet is formed by action of stochastic and quasilinear diffusion processes.

The generation and propagation of different plasma waves driven by fine-stuctured fast ion beams in the plasma sheet boundary layer was studied by analytical and numerical methods. It was found that low-frequency whistler waves as well as electron cyclotron waves and electrostatic emissions in the form of solitary and periodic nonlinear waves are available. Our results have shown that whistler waves, excited quasi-parallel to the background magnetic field, can be trapped during their propagation within small spatial regions where the ion beamlet density is enhanced compared to the density of adjacent regions, and so be observed in the form of magnetic noise bursts. Electrostatic emissions driven by warm ion beams make a contribution to the broadband electrostatic noise composed of a series of solitary pulses or of quasi-periodic waves and commonly detected in the plasma sheet boundary layer. Electron cyclotron waves contributes in narrow banded noise in the vicinity of the integer as well as half harmonics of electron gyro-frequency.

The nonlinear MHD structures in magnetospheric plasma were investigated. There were found two possible types of solitons: compressive and refractive. Their amplification due to the presence of ion beams have been examined. The results have shown that effective length of soliton-beam interaction could be only a few times more than soliton dimension. The life time of soliton determined by linear Landau damping can be much more then the time of its interaction with ion beam.

Recent INTERBALL-TAIL meauserments show that the bursts of energetic particles appear rather often in the different regions of the tail. We assume that the reason of the acceleration is local, spontaneous reconnection of the magnetic field, permanently occuring in the different regions with different intensities. Rather strong inductive electric field, rising in the course of the magnetic field topology reconstruction, is able to accelerate particles up to enrgies of several keV or even few meV. Rather simple model of the particle acceleration in the tail was constructed. In the framework of this model the power law spectra for ions and exponential spectra for electrons was obtained. For reference, the analysis of recent INTERBALL-TAIL meausuremnts have shown that protons in most of the cases have power law spectra (74 % of the statistics) or power law with the change of slope to more steep one for the energies more than 100 keV (14 %). For electrons exponential shape of the spectra is more frequent (47 %), and exponential with the power law "tail" for energies more than 100 keV (17 %) or pure power law (36 %) are also observed.

At the present time the great opportunity for the space physics is given by the comparison of simultaneous measuruments of different spacecrafts. Recent distant tail GEOTAIL meausuruments have found that a fairly stable structure of the tail extending at least to x=-200 Re behind the Earth. At the same time magnetic field observations of 3-D turbulent magnetic fields may be inerpreted as indication of the presence of tearing mode turbulence in the distant tail. The ion dynamics in a distant tail magnetic field configuration with a cross tail electric field and magnetic fluctuations driven by reconnection was studied numerically. Test particle simulations have shown that magnetic turbulence is very effective for maintaining the stationary structure of the current sheet and for the transmission of the ion acceleration due to the electric field to thermal motion. The values obatined for the bulk velocities and for ion temeparature are consistent with observed ones. The thickness of the of the current sheet increases with the level of fluctuations. A clear filamentation is observed for the level of fluctuations D B/Bo=0.1, while a more diffuse structure is obtained for D B/Bo=0.5. In a general way, the distribution of the current density and of the ion pressure indicates D B/Bo= 0.2 as a reasonable value for the level of magnetic fluctuations in agreement with obsrevations.

1.1. Dayside magnetopause observations with the fast plasma analyzer SCA-1 showed transient phenomena: number density, velocity, and temperature jumps and a leakage of hot magnetospheric ions into the magnetosheath that suggest non-stationary reconnection as the most probable reason for observed transients.

Plasma bursts observed after the first magnetopause crossing indicate nearly-continuous evolution in time as the satellite moves deeper into the magnetosphere: a decrease of transport velocity and number density, and a strong increase of temperature. The distribution function of ions in plasma bursts changes from fluid-like to beam-like systematically as time passes from the first magnetopause crossing. These changes suggest that the satellite observed the evolution of plasma clouds penetrating into the magnetosphere as a result of an instability at the magnetopause. Energy per ion increases as plasma clouds penetrate deeper into the magnetosphere suggesting the action of heating or an acceleration mechanism. Injected plasma clouds may provide a source of magnetospheric plasma.

Dispersive ion beams were observed at the magnetopause and at the edges of plasma clouds in the magnetosphere. This suggests the gyromotion of ions on the edge of the cloud, and allows one to estimate the spatial scale of observed events. These observations also suggest the erosion of plasma from the cloud’s boundary.

Inspection of dayside magnetopause crossings during 1996 showed that plasma bursts at dayside magnetopause are observed almost at every magnetopause crossing. Only two crossings without plasma bursts werer observed when IMF was northward and steady.

1.2. Observations of magnetopause at open field lines frequently show strong transient phenomena: number density, velocity, and temperature jumps. This strongly suggest reconnection as a reason for observed transients. One of most interesting cases was observed during arrival of large magnetic cloud to the Earth on October 18-19, 1995. The IMF orientation on October 19 (strong northward component and strong negative Y-component) facilitated reconnection on the side of the cusp connected to the dawn sector of the geomagnetic tail. Location of the Tail probe was quite close to nightside magnetopause in this sector of the tail. Several crossings of magnetopause was observed due to restructuring of the magnetosphere and associated decrease of the magnetic flux inthe tail. Most of the time when Interball-1 was observing magnetosheath-like plasma, strong variations of velocity magnitude, flow direction, temperature and number density are observed with fast ion spectrometer SCA-1. The typical calculated velocity variation ~100 km/s is about 50% of the Alfven velocity value in the magnetosheath (~220 km/s). Another reconnection signature is the double ion beams, that have been observed a significant fraction of the time the satellite was in the magnetosheath. These beams are separated by about 230 km/s, suggesting the second beam being reflected from magnetopause at the reconnection region. Bipolar variations of the magnetic field also indicates that reconnection is going on.

Comparison of measurements on the main satellite and subsatellite allowed one to estimate the velocities of MP motion for several magnetopause crossing during arrival to the Earth strong pressure pulses. This velocity sometimes was very high (up to 200-400 km/s).

1.3. Two examples of INTERBALL-1 data near high and low latitude tail magnetopause (MP) under disturbed conditions have been analysed: on October 18, 1995 (high latitudes) and on September 21, 1995 (low latitudes). For the high latitude case MAGION-4 data provide the opportunity to determine scales of MP current sheets which are of the order of 100-500 km for the main ones, of 50-200 km for FTEs and of a few km for the fine structures and ULF turbulence. MP speed was 15-30 km/s. The energetic protons in MSH provide an evidence of reconnection upstream spacecraft, the taiward flows grow for northward MSH magnetic field when reconnection site is believed to be shifted tailward cusp. The inner boundary layer (BL) after the disturbance consists from tailward and earthward plasma of MSH origin and cold mantle tailward one. The earthward flow is an evidence of reconnection tailward S/C, which is regarded as a specific feature of the disturbed conditions. Local production of PS-like plasma at high latitudes is argued based on the inner BL plasma characteristics. Following features are observed in both cases: (a) Flux Transfer Events (FTE) for both northward and southward MSH fields; (b) waves in the current sheet vicinities over ten mV/m and 15 nT peak-to-peak; (c) electron fluxes with scales down to few km with extra heating especially parallel to the magnetic field; (d) outer turbulent boundary layers with deflected magnetic field; (e) ions with time-energy dispersion like features and deflected ion fluxes. In the downstream dawn region at the transition between low latitude boundary layer and plasma sheet (LLBL/PS) multiple MP encounters are observed. In LLBL parallel electrons intensifications correlate with ULF magnetic fluctuations.

1.4. Case studies of the magnetopause crossings based on Interball Tail probe and Magion-4 subsatellite data. Several magnetopause crossings in different conditions and in different positions are presented: high latitude, equatorial, subsolar and flank. Magnetopause thickness and motion are estimated. Small scale structure of the magnetopause is described based on magnetic field, wave and plasma data from main satellite and subsatellite.

1.5. Low latitude boundary layer. The plasma transition from magnetosheath proper to magnetosphere occurs in a region with limited thickness around the magnetopause current layer, and such region is called boundary layer. The boundary layer has been found to be present everywhere along the magnetopause, and it's called the low-latitude boundary layer (LLBL) in the low-latitude range. Measurements performed by ELECTRON experiment onboard the INTERBALL-1 satellite reveal two types of low-latitude boundary layer electrons plasma: a high energy magnetospheric plasma with an average energy of about 2 keV and heated magnetosheath plasma with energy <1000 eV. Dominant population - core LLBL electrons -is a heated and often accelerated population from themagnetosheath and the hot magnetospheric population is generally strongly depleted or missing altogether. Dominant population have an average energy of the order of 100 eV and are systematically field-aligned and counterstreaming. As a trend the temperature of this electron population increases with decreasing distance to the Earth. An initial comparison between electron and magnetic field measurements indicates the core LLBL electrons coincide with a strong increase of the magnetic field. The resulting strong magnetic field gradient can explain why high energy population is strongly depressed in the LLBL region.

The preliminary results obtained from the ELECTRON experiment show that LLBL electrons are observed inside an unexpectedly large region of the dawn side of the magnetosphere - up to the 5 radii inside the magnetosphere.

1.6. Magnetosheath indications of magnetopause processes. Energetic spectra of protons in the magnetosheath (MSH) have usually power law shape with fluctuation due to magnetic field noise. Sometimes we observe on flanks of MSH during several minutes proton spectra (always for 2p-telescope looking 62° to sun direction) composed of two components - power law continuum and high energy peak.

Observations of energetic protons in the magnetosheath on August 10 1995 05:50 UT, when s/c position was Xgse=6.48, Ygse=-14.75, Zgse=-0.27; Ygsm=-13.88, Zgsm=5.01 (all in Re units), shows that at very begin of event the spectrum slope change its sign indicating existence of maximum at ~100 keV. First four successive spectra for the event show that maximum moves toward high energies from 200 keV to >700 keV. Total duration of the process is ~ 240 sec.

It seems most probable that these high energy peaks in proton spectra are due to proton escape from magnetospere during flux transfer events (FTE) on subsolar part of the magnetopause. Futher studies of DOK-2 data together with IMF data from other spacecrafts are necessary to elucidate the nature of these peaks and explain their behavior.

 2.1. The results of the first high time resolution two points study of the near-cusp BL displayed multiscale nonlinear structures therein. Rather well defined MP coexists with MSH plasma stagnation sites ("PSS") catched in the exterior cusp from both MP sides. Outside MP the PSS are bounded by magnetic barriers, the magnetic field inside PSS dropping by order of magnitude. The thermal energy excess inside PSS is close to the MSH dynamic kinetic energy. Energetic electrons presence inside PSS in the outer cusp throat (OT, which are outside MP) means that their magnetic field lines had been reconnected with the Earth ones, the thermal particle distributions agree with closed magnetic configuration.

Just outside MP the extremely turbulent layers exist with magnetic field and velocity vortices. The magnetic wave amplitudes provide nonlinear ion trapping. The characteristic scales are 300-5000 km, the latter corresponds to the PSS ones.

In OT ion flows along magnetic field are seen with dominance of the motion towards the cusp. They are separated from the turbulent layers. The electrons show pure isotropic MSH behavior in contrast to field-aligned bi-directional cusp ones. These outer counterparts of the cusp field lines seems to be isolated from inner magnetosphere by surface charges at MP, the potential barrier being evaluated as few hundreds V.

We suppose, that in PSS the primary MSH kinetic energy is transformed into the thermal one via multiscale cascades: reflection of the PSS from the magnetic field at the tailward OT ‘magnetic wall’ and in the OT cavity (large scales of 1-3 Re), nonlinear vortex-like waves of medium scales and, finally, at the micro scales ranging from ion gyroradius till electron inertial length.

Statistically the OT depth (deflection from the model MP towards the Earth) is 1-2 Re. The cusp is permanently seen from pericenter to MP, having X spread in SM frame from -2 to 7 Re, and the Y one +/- 7 Re. The MSH ion flows are permanently seen inside MP also in LLBL and at high latitude mantle field lines, the latter are much better defined on the morning side.

We briefly compare our near cusp findings with other INTERBALL-1 ones on the tail and dayside field lines (FTE, sunward ion flows due to reconnection, outer turbulent boundary layers etc.).

3. SHOCK

3.1. Monoenergetic Proton Beams from the Bow Shock. The region where unusual proton spectra with peaks are observed is the region upstream of the bow shock. Two examples analyzed show high flux and narrow peak at 95 keV and 38 keV with FWHM=21.8 keV and 9.4 keV, respectively. Duration of events was 20-30 sec. Angular distributions show that protons are coming from the bow shock. According to magnetic field data the s/c was magnetically connected to the region of quasiperpendicular bow shock. Proton flux reached 10⁴ s^-1 cm^-2 sr^-1 keV^-1.The energy flux corresponding was 1.4 10⁷ keV sm^-2 s^-1 .(comparable to solar wind energy flux), and the energy density 0.4 keV sm^-2 . It must be mentioned that magnetic field energy density was in this case of only 0.09 keV sm^-2. Electron flux was very small in both cases. Two possible sources of protons are: escape from magnetospere and shock drift acceleration. In both cases it is not easy to explain these high-intensity almost monoenergetic proton beams. The problem requires further study.

3.2. The dynamics of ion distribution function near the Earth's bow shock is studied on the basis of quasi-3D measurements of ion energy spectra in the range of 30 - 24200 eV/q with Russian-Cubian CORALL instrument on the INTERBALL/Tail Probe satellite.

The instrument was designed for observations of magnetospheric plasma and measures ions in angular range of 36 to 144 degrees from Earth-Sun direction. Ion populations generated by the Earth bow shock are often observed upstream from bow shock. In the solar wind a stream compressed and heated by passing of very dense magnetic cloud,two types of these ion populations were measured upstream and before the bow shock crossing on August 25, 1995 at 07:37 UT. Both populations were observed in the energy range above 2 keV. At 06:20 UT when angle between direction of interplanetary magnetic field and normal to bow shock was q _Bn ~ 43^o the instrument observed narrow fast (V ~ 800 km/s) field-aligned beam moving from the Earth. At 07:30 when q _Bn ~ 28^o the wide ion pitch-angle distribution was observed. The similar suprathermal ion population is observed in magnetosheath simultaneously with solar wind ion population heated and deflected from Sun-Earth direction. Similarity of observations during mentioned time interval and under usual solar wind conditions allows us to conclude that types of suprathermal ion populations upstream and downstream from bow shock do not depend on the solar wind disturbance generated by the magnetic cloud.

3.3. With the data of fast ion spectrometer SCA-1 on Interball Tail Probe we are testing the hypothesis, proposed on the basis of measurements on Prognoz-8 and Prognoz-10, that the thermalization of ion core on the strong Q-perpendicular shock front is provided by non-stationarity of the shock front. One supercritical Q-perpendicular bow shock crossing is analyzed. The downstream transmitted beam consists of multiple beams with thermal width of about upstream solar wind thermal width. This supports previous suggestion that the heated core of the downstream ion velocity distribution is formed of beamlets originating at patchy and oscillating structure of the shock front.