Written: Jul 25, 1994 by Vassilis
Modified: Sep 5, 1994 based on comments by Steve Christon and Christian Jacquey
Modified: Sep 14, 1994 based on comments by Don Mitchell and Don Williams
Modified: Oct 16, 1994 to provide to GEM campaign coordinators Lyons and Maynard
-----------------------------1993-MAR-17/18---------------------------
PERIOD: 2330-0130 UT
EPIC observed a velocity dispersed ion signature at 0020 UT lasting for about 15 minutes. Most energetic ions are seen first followed by less energetic ones. An electron beam is on either side of the ion intensification. Pancake distribution of ions is observed when the ion fluxes are low, probably indicative of mantle plasma.
-----------------------------1993-MAR-20------------------------------
PERIOD: 0130-0330 UT
This period is signified by the lack of intense ion fluxes until ~0310 UT. At that time a tailward proton/oxygen anisotropy is observed. Despite the lack of intense ion fluxes the electrons are present in high fluxes and exhibiting a moderate (factor of 5) tailward anisotropy.
PERIOD: 0330-0530 UT
EPIC observed a tailward proton anisotropy throughout the interval with fluxes most intense at 0355-0400 UT, at 0408-0418 UT and 0423-0435 UT.
-----------------------------1993-MAR-21------------------------------
PERIOD: 0000 - 0600 UT
EPIC observed tailward streaming of protons and oxygen. The fluxes of the ions increased in intensity at ~0340 UT and remained high until after 0600 UT. The most intense event of the period entire period between 0000-1000 UT started at 0555 UT. Tailward anisotropic electrons preceded the ion intensity increase by at least 2 science records.
-----------------------------1993-MAR-24------------------------------
At 0200 UT GEOTAIL was at the the lobe/mantle as a pancake distribution is observed at channel P2 (see C2 plot between 0200-0227). At 0227 an intensification of fluxes at all channels is seen (e.g. STICS channel HR0, ICS channels P2, M2). At 0242 UT the foil in front of the ICS detector is set (as signified by the line at the bottom of the panel, below the annotations) and as a result the fluxes at ICS become lower. The foil does not affect STICS channel HR0, though. HR0 shows the peak intensity of fluxes at around 0240 UT, i.e., before the foil was placed at ICS. At the time of peak intensity the fluxes were less anisotropic than during the beginning of the event, possibly signifying that the spacecraft was closer to the neutral sheet. After 0245 UT the fluxes decreased and became more anisotropic. The event is reminiscent of a PSBL-PS-PSBL crossing during a passage of a plasmoid/flux rope, that is usually accompanied by bipolar Bz and follows ground activity onset. However, this event lacks a clear bipolar Bz signature and we thus refrain from calling it a plasmoid.
-----------------------------1993-MAR-25------------------------------
PERIOD: 0430-0630 UT
EPIC observed tailward streaming throughout the interval. An intensification of the fluxes at ~0540 UT signifies probably heating of the plasma. Intense tailward anisotropy and fluxes are observed at 0600 UT lasting for about 8 minutes.
-----------------------------1994-JAN-11------------------------------
PERIOD: 0530-0730 UT
EPIC observed a flux intensification starting at 0605, predominantly in the protons. This was followed by Oxygen intensification at 0615. The fluxes of both species exhibit tailward anisotropy (factor of 100). The proton fluxes peak at 0635, considerably before the Oxygen fluxes, which peak at 0647. A second flux increase of the protons occurs after the Oxygen fluxes decrease. The proton flux increases are accompanied by mostly isotropic electrons. After the second proton flux increase an electron beam follows the gradual reduction of the proton fluxes.
-----------------------------1994-JAN-12------------------------------
PERIOD: 0350-0550
At 0405 a peak of ion fluxes seen in both protons and Oxygen, with earthward anisotropy. The flux increase is bounded between ~0400 and 0410 by pancake distribution ions reminiscent of mantle plasmas. The electrons are also anisotropic streaming earthward during this period (0400-0410) and also exhibit pancake type distribution along with the ions. The entry to the PSBL/PS is accompanied by significant duskward anisotropies indicative of a remote sensing of the approaching boundary.
At 0450 gradient anisotropy in both protons and Oxygen indicate an approaching boundary again. An electron beam is seen at the boundary and it is accompanied by an ion beam in both protons and Oxygen. The beams are streaming tailward. Within less than one minute the fluxes become less anisotropic and but still streaming tailward. The bipolar magnetic field signature and the associated energetic particle behavior point towards a tailwad moving plasmoid. The fluxes intensify in the second half of the plasmoid (after 0505 UT) in both electrons and ions, and the anisotropies become even more pronounced. The cutoff of the fluxes at the trailing edge of the plasmoid is quite sharp at 0518, with clear effects of remote sensing of a spatial boundary, and protons dissappearing first while oxygen decreases more gradually followed by an electron edge at the outermost edge of the plasmoid.
-----------------------------1994-JAN-13------------------------------
PERIOD: 00:00-0200
Earthward proton anisotropies between 0025-0037, followed by duskward-then tailward anisotropies. Intense fluxes do not start until 0045, and they are initially mildly anisotropic, then gradually more anisotropic. An abrupt exit to the lobe and re-entry to the PSBL/PS takes place between 0105-0110. Upon reentry, oxygen ions are peaked in intensity while ICS (60 keV) protons peak in intensity at 0123, later than the oxygen and the STICS (low energy) protons.
Electrons are mildly anisotropic with tailward anisotropy throughout most of the interval.
PERIOD: 0215-0415
Three distinct flux intensification events are seen at Geotail by EPIC. An earthward streaming one:
We wee both protons and oxygen and mildly anisotropic electrons between 0220-0235. Event also accompanied by significant gradient effects.
Two tailward streaming ones:
One between 0322-0335 with an electron beam at the edge of the lobe to PSBL interface, followed by ion beam that becomes more isotropic in the middle of the event and more anisotropic again at the trailing end of the event. The above signatures in conjunction with the magnetic field profile are reminiscent of a tailward moving plasmoid.
Another between 0405-0415, whereby an electron beam encompasses forward and trailing edge of the structure, which is also reminiscent of a tailward moving plasmoid.
-----------------------------1994-JAN-14------------------------------
PERIOD: 0000 UT - 1200 UT
1) 0530-0730 UT
Electrons isotropic throughout the interval except for at approximately 0718 UT when tailward electron anisotropy is evident lasting for 2 science records.
Protons (HRO H+) and Oxygen (M2 CNO) exhibit anisotropy reversals: At 0530 anisotropy is mild and earthward. At 0545 anisotropy becomes tailward. A Duskward anisotropy is seen at 0600 UT. It continues until 0620 UT. At 0620 UT the anisotropy becomes earthward and at ~0640 it switches to tailward. The tailward anisotropy continues throughout the rest of the plot (0730 UT). The anisotropy becomes the strongest at ~0710 UT.
PERIOD: 1600 UT - 2400 UT
1) 1600-1630
Prior to 1600 UT earthward and tailward ion anisotropies accompanied with duskward component gradient anisotropy. Tailward anisotropies become dominant at around 1600 UT. They continue until 1628 UT, when we enter the PSBL. We still pick up the duskward particles due to finite gyroradius effects at the lobe; those particles are still streaming tailward. Electrons are isotropic throughout this period, indicating closed field lines.
2) 1630-1700
Anisotropy is predominantly tailward with electrons isotropic until 1650. Between 1650 and 1703 electrons become more and more anisotropic with frequent beam-like behavior.
3) 1700-1730
At 1700 we almost exit to lobe. That skimming of the PSBL results in an electron beam followed by tailward streaming ions. The ion anisotropy switches to earthward at 1705 until 1712. At 1712 we exit to the outermost plasma sheet layers and see again- tailward streaming ions followed by electron beams. As we leave the PSBL or skim it three times these phenomena repeat (electron beams ion dispersion) and there is apparent gradient of energetic particles due to finite gyroradii effects.
During the above interval the electrons are isotropic at 1704-1711 and only during brief periods in the rest of interval.
It appears as if the current sheet energetic particles are streaming earthward but the PSBL particles are streaming tailward. Not infrequently we get contributions from both earthward and tailward populations and the total anisotropy is the result of one population being more abundant than the other.
4) 1730-1800
An entry to the PSBL at 1733 is accompanied by electron and ion
beams streaming tailward. Earthward ion anisotropy and isotropic electrons accompany the inner layers of the plasma sheet much like the previous crossings. There are no beams present at the lobe/PSBL interface at 1748. Electrons rise from near-background at 1753 and are isotropic, indicating closed field lines until after 1800. Ions are near background as foil is in position after 1747.
5) 1800-1930
Electrons are mostly isotropic in this period. ICS ions are most of the time at low flux levels, near background, due to presence of foil, until 1915. Occasionally between 1810 and 1830 the 60 keV ions exhibit duskward anisotropy indicating remote sensing of the hot plasma sheet.
At 1915 when the foil is released the ions are seen to stream tailward.
6) 1930-2030
Tailward ion streaming continues with quasi-periodic intensity enhancements. The character of the anisotropy changes at 1939: Ions become more beam like. No sign of electron beams but mild electron tailward anisotropy is present until 1947. The ion beams stop at 1954 but the electron beams start. Ions are still anisotropic, fluxes less intense, but electrons are more aniso- tropic frequently showing tailward streaming beams, until 2025. At 2025 electrons exhibit bidirectional anisotropy while the ions are still streaming tailward. Exit to lobe/outer PSBL at 2030. All species drop out except for H+.
Above interval is consistent with a plasmoid moving tailward. While at the earthward side of the plasmoid, we observe the post-plasmoid plasma sheet after 2000 UT.
Species are mostly H+ and He2+ (i.e., solar wind).
7) 2030-2130
We reenter the plasma sheet at 2040 UT. Frequent entries to and exits from the plasma sheet out to the lobe are accompanied by earthward ion beams, indicating activity has shifted tailward of Geotail. Electrons are isotropic (closed field lines). This may be considered as the neutral line having retreated tailward of Geotail. This scenario continues until 2140.
8) 2130-2240
Earthward anisotropies are replaced by tailward streaming at 2142 close to the neutral sheet. The absence of frequent crossings of the plasma sheet/lobe indicate a thick plasma sheet. The mild anisotropies present indicate that there is no beaming of particles but rather mild flows. Tailward flows are followed by duskward-then earthward flows until exit to lobe at 2230 UT.
H+ and CNO all participate: SW and ionospheric populations are both present during the flow reversal of 2130. Both SW and ionospheric contributors are also present between 2140-2230
9) 2240-2400
Reentry to plasma sheet at 2242. Ions are seen anisotropic in the tailward direction with electrons isotropic. Ion anisotropy becomes stronger at 2254 with beams interspersed within more mildly anisotropic particles. Ion anisotropy becomes gradually more pro- nounced until 2340. Fluxes begin to drop at 2320 as we exit to lobe. Electrons become mildly anisotropic at 2310 and exhibit beams at 2325. The above are reminiscent of tailward end of a plasmoid, whose core is at 2245-2305. This is like a FROP (Lui et al GRL 1994). Foil goes in position at 2315.