A GIF movie of images of the aurora in X-Rays, observed by the POLAR PIXIE imager is available here.
A Flare and a Coronal Mass Ejection were observed by the EIT and LASCO
instruments on the Solar and Heliospheric Observatory (SOHO)
at 14:00 UT on April 7.
Timeline of Solar Observations:
The flare was also recorded by the GOES geosynchronous satellites in agreement with the SOHO EIT and Yohkoh X-ray images.
- 14:00 - Flare
- 14:01 - 14:50 Shock
- 15:00 - CME
The WIND/WAVES instrument detected Type III emissions at 13:59
UT on April 7, consistent with the SOHO observations of the flare, followed closely by a Type II burst of radio waves (consitent with ground-based radio telescope observations from Potsdam, Germany and Nancay, France). This type II emission, associated with
the CME shock, was tracked from a fraction of a solar radii to about 10-12 solar radii and represents the first occassion that
WIND/WAVES and SOHO/LASCO/EIT have been able to make SIMULTANEOUS observations.
Based on SOHO observations and experience with previous events
of this nature, the SOHO team predicted the structure was travelling
towards Earth at a speed, in the plane of the sky, of 700 km/sec,
implying arrival at Earth by 00:00 UT on April 10.
**** UPDATE from 4/11/97, 12:00 EDT
In situ observations from the WIND and SOHO experiments detected
the possible arrival of solar ejecta material starting at around
00:00 UT on 4/11, preceeded by possible shocked sheath material
starting around 18:00 UT on 4/10. The solar ejecta material started
with a strong southward IMF possibly innitiating substorm activity.
In addition, the WIND WAVES team sees high thermal noise (starting around 13:00 UT on 4/10) indicating an increased ratio between the core and halo component of the electron temperature.
Ground-Based magnetometer measurements from the Canadian CANOPUS
array showed an intensification of activity, deflections of a few
100's of nT at around 01:30 UT on 4/11. The large storm commencement
was shortly after 03:00 UT on 4/11; deflections to -1000 nT were
The POLAR UVI imager detected an auroral brightening on the
dayside at 19:50 UT on 4/10; subsequently intense auroral activity
ensued beginning at approximately 22:26 UT on 4/10. Poleward edge of
the auroral oval in the midnight sector is observed to start
expanding toward the magnetic pole at approximately 22:32 UT.
From Geoff Reeves: The team from the LANL geosychronous satellites
reported a decrease in fluxes of energetic particles (electrons and
protons) at about 1745 UT on 4/10. The decrease in electrons with
energies of 0.7-1.8 MeV on satellite 1994-084 was about a factor of
10. That satellite was very near midnight local time. In the lower
energy (10s-100s keV) particles it looks very much like a growth
phase for a substorm. The decrease in fluxes occurred over about 10
min as opposed to the "classic" 0.5-1.0 hour growth phase. While this
is not the "typical" behavior I also wouldn't say it was all that
"unusual" - i.e. if we weren't expecting the CME to hit I wouldn't
have taken note.
Addition from Geoff Reeves: What we saw was a fairly abrupt drop in the energetic particle fluxes on the night side starting at about 17:45 UT on April 10. This was associated with an earthward motion of the plasma sheet as seen in the MPA plasma data. The
fluxes remained depressed until about 2240 UT when we saw the first injection. Injection activity continued but diminished over the next 8 hours. There was certainly a solid magnetospheric reaction but Dst remained around 0 and the injection activity was
not unusually strong.
Eyewitness reports of aurora in New Hampshire on the evening of
Eyewitness reports of aurora seen overhead at Millstone Hill Observatory, Gloucester and Boston in Massachussetts on the evening of 4/10.
From J. Steinberg: The WIND/SWE data at about 13:45 UT on 4/11
show about 8% alpha/proton ratio - another indicator of ejecta,
suggesting this was indeed connected with the CME emitted on 4/7.
From T. Onsager: Observed stretching of the magnetotail is evident
from the decrease in electron fluxes seen by the GOES satellites.
From R. Greenwald: A big equatorward push in the convection
region was observed using the SuperDARN radar between 02:00 and 04:00
UT on 4/11.