Volt Lutsenko

Plasma sheet ion injections into the auroral bulge: Correlative study of spacecraft and ground observations

Multiple and sporadic time-of-flight velocity dispersed ion structures (TDIS) are systematically observed above the ionosphere at ∼3 Re altitude by Interball/Auroral spacecraft near the poleward edge of the auroral bulge. These events represent direct snapshots of the impulsive ion acceleration process in the equatorial plasma sheet which allow us to study the details of the connection between ionospheric and plasma sheet manifestations of the magnetospheric substorm. Two events are analyzed during which the spacecraft footpoints passed over the Scandinavian ground network. We found that the TDIS correlate with the intensifications of westward current and auroral activations at the poleward edge of the bulge, which confirms the association of these dispersed ion beams with the temporal evolution of impulsive reconnection in the tail. Furthermore, we present direct evidence of an active neutral line in the magnetotail during one of the events using plasma sheet measurements made concurrently by the Interball/Tail and Geotail spacecraft. The 2–3 min repetition period of these ∼1 min long activations indicates a fundamental time constant of the substorm instability. On the other hand, the estimated injection distances of the energy-dispersed ions were inferred to be smaller than the estimated position of the reconnection region in the tail. We also found that the TDIS ion beams are released within the closed plasma flux tubes deep inside the plasma sheet, and yet they are synchronized with auroral activations at the poleward boundary. These facts imply that the ion beams are formed in a spatially extended region of the plasma sheet rather than in the close vicinity of the neutral line. We argue that braking of the reconnection-induced fast flow bursts when they interact with the closed plasma flux tubes and the earthward propagating fast wave electric field generated in the braking region may be important in forming the observed multiple, sporadic, energy-dispersed ion beams.

Almost monoenergetic ions near the Earth's magnetosphere boundaries

More than 200 cases of energetic ion beams with an energy spectrum consisting of 1–3 narrow lines were observed during a period from August 1995 to August 1998 in the Earths magnetosheath and in the region upstream of the Earths bow shock. The observations are from the DOK-2 experiment on board of the Interball-1 spacecraft. Because the relative width at half maximum of these lines is of only 15–30%, we use the term “Almost Monoenergetic Ions” (AMI) for these events. Ion energy values varied for different events from 30 to 600 keV but were almost unchanged during each event. In two peak spectra the energy values ratio was 1:2 and in three peak spectra the ratios were 1:2:(5–6). Such line spectra cannot be explained by current models of particle acceleration or escape from the magnetosphere. We propose a hypothesis explaining the origin and main features of AMI as solar wind ions acceleration in a strong electrostatic field burst in a small region, possibly on the magnetopause or on the bow shock.

Cusp and boundary layer observations by INTERBALL

Abstract Interball Tail Probe was launched on August 2, 1995 together with its subsatellite MAGION-4 into a highly elliptical orbit with apogee at 31 RE and inclination 63 degrees. During the course of one year all local times are visited. In this paper we will present initial results obtained from measurements in the cusp, mantle and eveningside plasma sheet in January, 1996. It is found that the cusp was well defined and persistent at altitudes of 4–10 RE. In one case both the main satellite and the subsatellite were in the cusp proper for two uninterrupted hours. We believe this to be the first ever multi-point satellite observation of the high-altitude cusp. The data indicate that the cusp was very stable with a wide entry area and that plasma entry took place at high latitudes rather than at the subsolar point. Pressure pulses, possibly due to Alfven waves were found. Sunward and antisunward moving plasma was measured simultaneously during a case of northward IMF but no convection was discovered. Plenty of plasma of cusp/magnetosheath type was also found mixed with plasma sheet plasma both equatorward of the cusp and in the eveningside plasma sheet.

Anomalous interaction of a plasma flow with the boundary layers of a geomagnetic trap

Using the data from the Interball-1, GEOTAIL, THEMIS and CLUSTER satellites, we propose a mechanism of anomalous magnetosheath dynamics. This mechanism yields that plasma boundaries can be locally deformed over distances comparable to its thickness. In particular, the magnetospheric boundary, the magnetopause, is deformed over distances up to a few Earth radii (RE) under the pressure of supermagnetosonic plasma streams (SPSs), instead of reacting to plasma pressure decreases, as it was previously thought. Supermagnetosonic plasma streams having a kinetic pressure a few times larger than the solar wind pressure and the magnetic pressure behind the magnetopause, can crush the magnetopause and even push it outside the mean bow shock position, as determined through the average pressures balance. Anomalous magnetosheath dynamics is initiated by plasma flow anomalies (FAs), triggered by rotational discontinuities, by jumps in the solar wind pressure and by interplanetary shocks, which all interact with the bow shock. We show that the generation mechanism for SPSs, adjacent to the FA, is connected with the compensation of the FA flow reduction by the SPS enhanced flow, which is produced by polarization electric fields at the FA edges. Statistically, SPSs are extreme events, relayed with intermittency and multifractality inside the boundary layers of the geomagnetic trap. In this way, SPSs provide “long-range” interactions between global and microscales. A similar role may be played by fast concentrated flows in the geomagnetic tail, in fusion devices, in astrophysical plasmas and in hydrodynamics.

INTERBALL magnetotail boundary case studies

Abstract We present two examples of INTERBALL-1 data near both the high and low-latitude tail magnetopause (MP) under disturbed conditions. For the high-latitude case, MAGION-4 data determine the scales of the MP current sheets which are in the order of 100–500 km for the main ones, 50–200 km for Flux Transfer Events (FTEs) and a few km for the fine structures and ULF turbulence. The MP speed was 15–30 km/s. The energetic protons in the magnetosheath (MSH) provide evidence of reconnection upstream of the spacecraft (S/C). The tailward flows grow for the northward MSH magnetic field when the reconnection site is believed to be shifted tailward of the cusp. The inner boundary layer (BL) after the disturbance consists of tailward and earthward flowing plasma of MSH origin and cold mantle plasma flowing tailward The earthward flow is evidence of reconnection tailward of the S/C, which is regarded as a specific feature of the disturbed conditions. Local production of a plasma-sheet-like plasma at high latitudes is argued based on the inner BL plasma characteristics. The following features are observed in both cases: (a) FTEs 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 a few km with extra heating especially parallel to the magnetic field; (d) outer turbulent boundary layers with a deflected magnetic field; (e) ions with time-energy dispersion-like features and deflected ion fluxes. In the downstream dawn region at the transition between the low-latitude boundary layer and the plasma sheet (LLBL/PS), multiple MP encounters are observed. In the LLBL parallel electron intensifications correlate with ULF magnetic fluctuations.

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.

Energetic ions upstream of the Earth's bow shock: INTERBALL-1 survey

Abstract A statistical survey of energetic ions (> 20 keV) observed by the DOK2 experiment on Interball-1 during foreshock intervals from 1996 to 1998 is presented. Flux levels depend on the connection geometry, with higher values at quasi-parallel shocks, particularly at lower energies. The decrease of flux in diffusive events with distance from the bow shock is consistent with results from earlier surveys performed closer to the bow shock. The energy spectra are softer for quasi-parallel than quasi-perpendicular connections. The reflected ions have musch softer spectra. The cumulative frequencies for flux level occurrence patterns exhibit differences for quasi-parallel and quasi-perpendicular geometries up to approximately 200 keV.

Medium energy proton fluxes outside the magnetopause: INTERBALL-1 data

Abstract The extensive data set of the DOK2 energetic proton measurements indicates a decrease of flux at 22 – 29 keV based on the distance from the magnetopause within the magnetosheath. In the region upstream from the bow shock the signatures expected for the preferential acceleration of protons at quasiparallel shocks are found in the data. In addition to the proton leakage from the magnetosphere observed in several experiments, the observations confirm the importance of bow shock acceleration for the population of medium energy protons in the near upstream region.

Acceleration of electrons at the quasi-perpendicular bow shock according to intershock data

Abstract The structure of intense fluxes of energetic electrons ≳ 30 keV observed near the quasi-perpendicular bow shock is investigated. It is shown that electrons are accelerated only in the cases when the angle θ Bn between magnetic field lines and the normal to the shock surface is very close (± 2°) to 90°. This result is in a good agreement with the theory.

The Structure of Ion Spectra in Outer Regions of the Ring Current: The November 13, 1995 Event

We present the results on variations of ion spectra in the energy range from 1 keV to 3 MeV. The spectra measured onboard the INTERBALL Tail Probe satellite on November 13, 1995, during the satellites passage from the dipole field lines to the lines stretched into the magnetotail are analyzed. The data of the CORALL, DOK-2, and SKA-2 instruments are used to reconstruct the ion spectra. It is shown that, when the ion spectrum along the satellite trajectory is averaged over 2-min intervals, it is smooth up to geocentric distances of 6RE. With decreasing distances, the form of the particle spectra in the region under consideration remained virtually unchanged (region from L = 11RE down to L= 6RE) and only insignificant variations of the energy of the spectral maxima are observed. Possible reasons for the observed regularities are discussed.