M. N. Nozdrachev

Magnetopause motion driven by interplanetary magnetic field variations

We use previously reported observations of hot flow anomalies (HFAs) and foreshock cavities to predict the characteristics of corresponding features in the dayside magnetosheath, at the magnetopause, and in the outer dayside magnetosphere. We compare these predictions with Interball 1, Magion 4, and GOES 8/GOES 9 observations of magneto-pause motion on the dusk flank of the magnetosphere from 1800 UT on January 17 to 0200 UT on January 18, 1996. As the model predicts, strong (factor of 2 or more) density enhancements bound regions of depressed magnetosheath densities and/or outward magnetopause displacements. During the most prominent event, the geosynchronous spacecraft observe an interval of depressed magnetospheric magnetic field strength bounded by two enhancements. Simultaneous Wind observations indicate that the intervals of depressed magnetosheath densities and outward magnetopause displacements correspond to periods in which the east/west (By) component of the interplanetary magnetic field (IMF) decreases to values near zero rather than to variations in the solar wind dynamic pressure, the north/south component of the IMF, or the IMF cone angle.

Multispacecraft measurements of plasma and magnetic field variations in the magnetosheath: Comparison with Spreiter models and motion of the structures

Abstract Large (from tens of percent up to several times) ion flux (or density) and magnetic field magnitude variations are typical magnetosheath features. Case and statistical comparisons of simultaneous solar wind observations, magnetosheath observations, and the gasdynamic model for the magnetosheath flow of Spreiter et al. (Planet. Space Sci. 14 (1966) 223) show that two types of magnetosheath plasma and magnetic field variations exist: • in some cases, they are a repetition or amplification of solar wind or IMF disturbances which pass through the bow shock; • but in the most cases, these variations are endogenous; i.e., they originate inside the magnetosheath. Persistence times and/or correlation lengths for the magnetosheath plasma variations were investigated via detailed comparison of simultaneous magnetosheath measurements from several spacecraft. For small separation distances (about 0.5RE) we used the satellite pair INTERBALL-1/MAGION-4; for larger distances (up to 10–30RE on the same or on the opposite flanks of the magnetosheath) we used the INTERBALL-1/GEOTAIL/IMP 8 measurements. In some cases, we observed a remarkable coincidence of the magnetosheath plasma behavior from the spacecraft separated by more than 10RE. It seems that the compression plasma structures move tailward together with the magnetosheath plasma flow.

High and low frequency large amplitude variations of plasma and magnetic field in the magnetosheath: Radial profile and some features

Abstract Variations in magnetosheath parameters, such as the ion flux and the magnitude of the magnetic field, over a wide range of frequencies are much larger than the variations in the undisturbed solar wind. We present the results of a statistical investigation of magnetosheath variations using a large database of high time resolution (ls) INTERBALL-1 measurements and 1 min resolution IMP 8 data. Radial profiles of the ion flux and the standard deviations of the ion flux on 1-minute intervals were obtained for dusk and dawn flanks of the magnetosheath. These profiles are similar on the dawn and dusk flanks of the magnetosheath and for high and low frequency variations. The amplitude of the high frequency variations depends on the angle between the bow shock normal and interplanetary magnetic field direction; variations are much larger behind quasi-parallel bow shocks.

Ramp nonstationarity and the generation of whistler waves upstream of a strong quasiperpendicular shock

A number of models have been proposed to explain the observation of low frequency (LF) whistler waves in the upstream region adjacent to the ramp of the quasiperpendicular part of the Earths bow shock. One such model relates these waves to the nonlinear dynamics of the ramp itself. Two aspects of this model, the plasma frame spectrum of the turbulence and the occurrence of nonlinear waves propagating away from the shock in the upstream region have already been shown to be in agreement with observations. A third aspect, the interaction and energy transfer between these nonlinear waves and the whistler turbulence, is studied by applying high order spectral analysis to Interball magnetic field data. Evidence for the nonlinear coupling between these two types of waves and the possible transfer of energy are presented.

Turbulent Boundary Layer at the Border of Geomagnetic Trap

A new phenomenon was discovered on the basis of analysis of the Interball project data. A hot plasma flow is thermalized through the formation of “long-operating” vortex streets and local discontinuities and solitons in a distributed region over polar cusps. Plasma percolation through the structured boundary and secondary reconnection of fluctuating magnetic fields in a high-latitude turbulent boundary layer account for the main part of solar wind plasma inflow into the magnetospheric trap. Unlike local shocks, the ion thermalization is accompanied by the generation of coherent Alfvén waves on the scales ranging from ion gyroradius to the radius of curvature of the averaged magnetic field, as well as by the generation of diamagnetic bubbles with a demagnetized heated plasma inside. This “boiling” plasma has a frequency region where the spectrum is different from the Kolmogorov law (with slopes 1.2 and 2.4 instead of 5/3 or 3/2). The fluctuation self-organization in the boundary layer (synchronization of three-wave decays) was observed on certain frequency scales.

The January 10–11, 1997 magnetic cloud: Multipoint measurements

The WIND and IMP 8 spacecraft detected a magnetic cloud upstream of Earths bow shock on January 10–11, 1997 while the INTERBALL-1, MAGION-4, GEOTAIL, and LANL-084 satellites were in the vicinity of the magnetopause and crossed it many times. Based on these multipoint observations we have determined the velocity of the magnetopause motion induced by the abrupt changes in the solar wind dynamic pressure during this event, and also the velocity of propagation through the magnetosheath of the structures connected with the magnetic cloud. Using the determined velocities, we tried to find the spatial orientations and dimensions of the observed disturbances. The estimated orientation of the interplanetary shock driven by the magnetic cloud is interpreted as a consequence of the local deformation of the cloud surface. The timing of measurements made by the aforementioned satellites suggests that the strong density enhancement behind the magnetic cloud is limited in spatial extent. We attribute this enhancement to the interaction of the magnetic cloud with the ambient solar wind plasma.

Plasma and Magnetic Field Variations in the Magnetosheath: Interball-1 and ISTP Spacecraft Observations

The results of an experimental study of plasma and magnetic field fast variations in the magnetosheath are presented. A comparison of the measurements with predictions following from gasdynamic model was made on different time scales. It is shown that variations of magnetosheath parameters cannot be explained neither by variations in the interplanetary medium nor by a motion of the magnetosheath as a solid body. These variations are several times larger than simultaneous solar wind plasma and interplanetary magnetic field variations on the same time scale. The level of these variations was studied as a function of the direction of IMF. Performed comparison of simultaneous magnetosheath observations carried out by IMP 8, GEOTAIL, and INTERBALL-1 has shown that the observed variations can be considered as structures originating in the subsolar region and propagating downstream with the magnetosheath speed.

PROJECT INTERSHOCK: COMPLEX ANALYSIS OF THE BOW SHOCK CROSSING ON 7 MAY 1985

Abstract Complex analysis of the bow shock crossing of Prognoz 10-Intercosmos satellite on 7 May, 1985, indicates that two different groups of electrons with the energies 30–100 keV and 5–10 keV are observed near the shock front. This reguires at least two different acceleration mechanisms to explain their nature.

Solar wind structure dynamics by multipoint observations

Abstract Six-hour segments of simultaneous solar wind plasma and interplanetary magnetic field data from RAP 8, WIND and 1NTERBALL-1 are used to compare correlations of the plasma and interplanetary magnetic field for the same solar wind structures. Magnetic field structures are, on average, as well-correlated as plasma structures. The averaged on large statistics cross-correlation coefficient is equal to 0.75 for ion flux and 0.71 for IMF magnitude comparison. But for many individual 6-hour segments the difference between plasma and IMF correlations is rather large. We find that good IMF correlations coincide with good plasma correlations 65% of the time but that good plasma correlations coincide with good IMF correlations only 44% of the time. Also the dependence of ion flux correlations on the IMF cone angle was studied for two sets of data. The plasma correlations increase as the IMF cone angle increases, suggesting plasma structures may be elongated parallel to the IMF.

The role of nonlinear interaction in the formation of LF whistler turbulence upstream of a quasi‐perpendicular shock

The role of the nonlinear interaction in developed low-frequency turbulence has been experimentally studied upstream of the ramp of a quasiperpendicular shock. The study has been carried out by application of the methods of bispectral analysis and wavelet decomposition to the Active Magnetospheric Particle Tracer Explorer Ion Release Module and Interball Tail Probe magnetic field data. It is shown that three-wave processes play a key role in the formation of the spectrum of the turbulence. Experimental results presented and previous theoretical considerations lead to the conclusion that energy is transfered from a narrow maximum frequency pumped by nonlinear dynamic processes to lower and higher frequencies.