ISTP Sun-Earth Connections 
April 7-11, 1997

image from polar's uvi instrument

Observations by the POLAR Ultra Violet Imager at 01:21 EDT on April 11, 1997, showing the aurora coming down past the US-Canada border (note Hudson Bay northward of the bright aurora region).

An GIF movie of these POLAR UVI images is available here.

A GIF movie of images of the aurora in X-Rays, observed by the POLAR PIXIE imager is available here.

Click here to see a view of the Aurora over Boston and Comet Hale-Bopp.

Access to Data and Information:

Event Summary (as of 15:00 EDT, 4/11/97)

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.

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 recorded.

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 4/10.

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.

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Last Updated: 04/11/97