SUBSTORM EVENT ON NOVEMBER 24, 1996

Prepared by V.A.Stepanov, A.A.Petrukovich, Yu.I.Galperin, V.A.Sergeev, Yu.I.Yermolaev, L.M.Zelenyi, R.A.Kovrazhkin

This is a preliminary summary of the event on November 24, 1996, considered during the INTERBALL Workshop in Kiljavanranta, Finland, February 1998. The main attention at the INTERBALL workshop was devoted to the activation at 21:45 UT and onset at 22:27 UT.

Substorm Overview

21:10 UT   Start of the growth phase
  • IMF becomes southward
  • start of pressure increase in the magnetotail
    • 21:10 - 22:00 UT   Pronounced plasma sheet thinning (Bz decrease)
    21:48 UT   Localized activation (pseudobreakup?) - see below
    22:25 - 22:27 UT   Onset of the expansion phase
  • pressure maximum
  • plasmasheet flow becomes tailward
    • 23:07 UT   Start of recovery, pressure minimum


    SUBSTORM ONSET TIMING

    22:25 UT   Breakup at Amderma
    Start of sharp plasmasheet pressure increase (by GEOTAIL)
    22:27 UT   Breakup at other stations (IMAGE, Dixon, Leirvogur, Niemegk)
    Plasmasheet pressure maximum (by GEOTAIL)


    PRELIMINARY CONCLUSIONS

    1.  First (local?) sign of onset at 22:25 UT at Amderma MLT (dawnward of GEOTAIL).

    2.  Global onset at 22:27 UT in the magnetotail, at nightside auroral zone and midlatitude magnetometers.

    Activation At 21:45 UT

    Pulses in the solar wind and IMF during southward IMF Bz period
    A change in the IMF Bz (from -5.5 to 0 nT), solar wind plasma density and velocity variations, at 21:25 UT.

    Particle burst observed inside the Polar Cap and in tail lobes
    A short burst of particles detected by the Auroral Probe particle detectors during the Polar Cap crossing at 21:45 UT, almost simultaneously with the Tail Probe detectors registration of the particle burst inside the North Lobe.

    DATA DESCRIPTION

     During the growth phase, an interesting feature was detected in the solar wind: a small perturbation in Bz near the 21:25 UT (change from -5.5 to 0 nT), also seen in the plasma parameters. According to the WIND position (Xgsm = 72 Re, Ygsm = -18 Re) and particle velocities, time delay needed to take into account solar wind travelling time is approximately 18 minutes.

     The LANL-080 picture shows the electron intensity profiles at the geosynchronous orbit. A small dip indicated by the black line is most probably caused by the magnetic field decrease, unfortunately unsupported by the onboard magnetometer measurements because of their absence.

     Magnetometers data from some ground stations could be seen here. The pseudobreakup at 21:48 UT, probably related to the observed IMF disturbance, is indicated by the left black line. The look of these magnetograms imply that there was a current between Tromso and Kiruna.

     The INTERBALL Auroral probe particle detectors observed a particle burst inside the Northern Polar Cap. ION particle spectrometer data are presented here separately for electrons and ions. It is seen that particle energy lies below 1 keV.

     The INTERBALL Tail probe ELECTRON particle spectrometer data snapshot taken in the North Lobe shows a burst of electrons of 1 keV and below, rather isotropic, but somewhat like counterstreaming at 143 eV energy. CORALL particle spectrometer data detected 1 keV ions.

     The INTERBALL Tail probe detected ion burst a minute later than its subsatellite MAGION-4 (top panel), located 2000 km earthward from the Tail probe. On the bottom panel there is a Tail probe plasma flux, on the middle panel - MAGION-4 plasma flux.

     It should be pointed that Auroral and Tail probes detected particles of almost the same energy. Here is a picture representing the respective positions of the satellites in GSE coordinate system. The field lines on which Auroral and Tail probes were located, being traced to 100 km altitude, appear to have a very close position in the ILAT-MLT frame, and close to the IMAGE longitude.

    SUMMARY

    1. A plasma burst observed inside the Polar Cap by the Auroral probe detectors. Similar burst observed by the Tail probe in the North Lobe.

    2. From the ground-based magnetometers data, a pseudobreakup was seen at the moment corresponded to the burst.

    3. Detected solar wind disturbance might approximately (considering the appropriate time delay) be related to the burst.

    4. The plasmasheet pressure pulse was seen by GEOTAIL at the moment of the plasma burst registration.

    UNCLEAR QUESTIONS

    1. The solar wind mini-cloud and the plasma burst:

    2. The plasma burst: where did it come from?

    ACKNOWLEDMENTS

    1. Auroral and Tail probes:

    2. WIND data:

    3. GEOTAIL data:

    4. LANL data:

    5. IMAGE data:

    6. Amderma, Dixon data:

    We are grateful to S.Perraut and T.Bosinger for valuable comments during the discussion.