Events on January 10-11, 1997 - INTERBALL observations

The large magnetic cloud caused by coronal mass ejection at the Sun on January 6, 1997 came to the Earth at early morning on January 10 and continue to interact with Earth's magnetosphere till January 11 (see for example home page of this event prepeared by Dr. M.Peredo http://www-istp.gsfc.nasa.gov/istp/cloud_jan97/event.html). Here we present some preliminary INTERBALL-1 measurements for these events made by many its instruments (for the description of them and PIs see http://www.iki.rssi.ru/tail/list.html).

During the days discussed here INTERBALL-1 satellite was in the magnetosphere (MS) near its dusk flunk - see the Fig.1 for compearing.

Due to magnetosphere compression by ion density increasing at the shock wave on the leading edge of the cloud INTERBALL-1 crossed the magnetopause (MP) several times during the interval 01-11 UT on January 10 - see the position of the first crossing on the Fig.1 and the plots of ion flux (by VDP instrument) and magnetic field ( by FM-3I instrument) behavior on the Fig. 2, 3.

Several features of the magnetopause crossings and magnetosheath (MSH) and magnetosphere (MS) observations are shown on the Fig. 4 (ion dynamic spectrograms and plasma bulk parameters at the MSH/MS by CORALL instrument), Fig. 5 (electron energy-time spectrograms by ELECTRON instrument) and Fig.6, 6a (fluxes of energetic particles - protons and electrons at the range about 20-100 keV by DOK-2 instrument).

Fast (~10 s) 3-D ion velocity distributions from SCA-1 plasma analyzer are available in the time interval 03:30 19:30 UT on January 10. Several magnetopause crossings witin the time interval from ( 03:31 till ( 05:13 UT can be identified from the dynamic spectra (Fig. 7 a and c) and calculated moments (Fig. 7 b and d). Reconnection signatures in the magnetosheath: ion flux dropouts, double beams and plasma jetting are seen in upper four dynamic spectra (sunward hemisphere), as well as short-period bursts of ions in lower 4 dynamic spectra (untisunward hemisphere). Measurements in the tail also show reconnection signatutes and indicate newly injected plasma.

The MP positions at the crossings observed on January 10, 1997 are not differ significantly from the average MP position (Fig.1), because the increasing of the plasma pressure isn't very high. Indeed, the ion flux at the MSH equal (in maximum) about 6E+08 cm-2s-1 (Fig.2). For velocity about 300 km/s (Fig.5) it gives us the value of dynamic plasma pressure about 3 nPa - not far above the average value (2 nPa). As is seen from Fig. 2, 4, 6 the moments of MP crossings observed by integral Faraday cup (VDP), ion (CORALL) and electron (ELECTRON) spectrometers coincide very well (including a short (20 min.) exit to MSH around 11.10 UT). As it's seen from ion and electron energetic spectra, before magnetic cloud arrival INTERBALL-1 was located on the closed field lines in the plasma sheet. After MP crossings satellite moved through boundary layers, tail lobes and returned to the disturbed plasma sheet.

Necessary to mention the unusual behaviour of magnetic field in this period (Fig. 3) - field magnitude strongly increases when satellite exits to MSH and field is directed mainly along Xse axes. Fluxes of energetic protons (Fig.6,6a) increase strongly near the multiple MP crossings at 3:20-4:20 UT and at the distubed plasma sheet.

The most dramatic features took place at the early morning on January 11 when the trailing edge of this cloud came to the Earth (see Fig. 8 - ion flux by VDP , Fig. 9 - magnetic field by FM-3I, Fig. 10 - ion dynamic spectrograms by CORALL, Fig. 11 - electron energy-time spectrograms by ELECTRON) .

These pictures also show us the several MP crossings during interval 1 - 3:30 UT. The ion density at the trailing edge of the cloud has a huge value - about 20 times (!) more than the average values for the solar wind. Due to such increasing of density magnetosphere was strongly compressed and the INTERBALL-1 observed several magnetopause crossings at the distance about 7Re closer to the Earth relative to the average one - see the position of the first one on the Fig. 1.

The value of ion flux at the interval 01.20-02.10 UT was about 5.2E+09 cm-2s-1 (see the Fig. 8) and sometimes above the upper threshold of VDP instrument (never observed before during 1995-1996). For the bulk velocity about 300 km/s (see Fig.10) it means the highest ion density more than 170 cm-3 (!!!). These values of velocity and density give us the dynamic plasma pressure about 40-50 nPa. The model magnetopause position calculated for such high pressure coincides well with INTERBALL-1 observations - see light lines at the Fig.1

The value of magnetic field at the magnetosheath wasn't very high during this interval - about 30-40 nT. The field at the MSH was directed mainly perpendicularly to Xse (Bx-component is very small - about 5 nT, but Bz equal about 20-35 nT) - see the Fig. 9.

Many features of plasma flow at the magnetosheath and magnetosphere at this interval are observed by CORALL and ELECTRON instrument - see the Fig. 10, 11. The ion and electron energy spectrogram obtained at the morning on January 11 show clearly the MSH measurements from 01:20 till 02:10 UT in accordance with other instruments. Processing of ion data allow us to determine the ion bulk velocity and the ion temperature at the MSH and MS.

Comparing of VDP and CORALL density estimation show us that at the discussed period the ion flow at the sheath consist from very dense and cold core recorded by VDP and hot halo with low density, measured by CORALL because its acceptance cone is deflected by 20 deg. from Sun-Earth line.

It is interesting to note that electrons with energies 30 - 200 eV demonstrate bidirectional streaming along the magnetic field direction (which coincide with X-axis) in the time intervals 2.30 - 3.15 UT, 3.37 - 3.55 UT and later on January 11. At the same times the very intensive ion flow with energy 100 - 1000 eV is seen as the signature of the boundary layer

It 's necessary to emphasize that comparison of INTERBALL-1 observations during January 10-11, 1997 with the similar ones made onboard WIND and GEOTAIL spacecraft gives us in the most of points very reasonable qualitative and quantitative agreement.

This material was prepared by INTERBALL scientific team members - G.Zastenker, P.Eiges, A.Fedorov, M.Nozdrachev, N.Borodkova, K. Kudela, O. Vaisberg, L.Avanov, V.Smirnov, A.Skalsky, N.Nikolaeva, V.Lutcsenko, Yu.Yermolaev, P.Dalin