SSDOO Supports Solar-Terrestrial Event Study

Volume 13, Number 1, March 1997
By Mauricio Peredo

The Coronal Mass Ejection (CME) - Magnetic Cloud Event of January 6-11, 1997, has generated a great deal of interest in the space physics community. Detailed studies of the period are well underway among the International Solar-Terrestrial Physics (ISTP) teams and collaborating missions and observatories. The NASA Space Science Data Operations Office (SSDOO) is contributing to these efforts by making all the ISTP Key Parameter data available electronically via the CDAWeb system at URL http://cdaweb.gsfc.nasa.gov. Users can readily produce plots or ASCII listings of the available data. For reference, a summary of the event follows.

Event Summary

For the first time ever the satellites of the ISTP "Observatory" have tracked a solar eruption all the way from a CME expelled from the Sun, through interplanetary space, until it hit the Earth's magnetic environment, causing there violent disturbances and spectacular auroral displays. The initial expulsion occurred on the Sun on January 6, 1997, and a resulting magnetic cloud hit the Earth on January 10, 1997.

The ISTP "Observatory" tracks a Sun-Earth Connections Event.

The Sun often erupts. It flings out white-hot ionized gas (actually hotter than white-hot, to where it glows in X-rays) with explosive violence. Only occasionally is this gas aimed at Earth, however, and it is even more unusual for scientists to be watching the potentially disruptive mass ejection (as they were in this case) just as it leaves the Sun. This fact made it possible to alert other scientific teams of possible activity they might observe two to three days later, that being the time normally required for such ejecta to traverse the 93-million mile void from Sun to Earth. Thus, while this was not the first or the largest event of this nature to be detected, the ISTP "Observatory" includes a complement of spacecraft and ground-based missions that allow study of this "space storm" on a scale never accomplished before.

Observation of the Coronal Mass Ejection leaving the Sun from the SOHO/LASCO instrument.

Initial evidence of the event was reported during an ISTP Science Workshop at NASA's Goddard Space Flight Center on January 7-9, 1997. Scientists from the joint NASA-European Space Agency satellite SOlar and Heliospheric Observatory (SOHO) showed evidence that a CME, directed toward Earth, had been emitted from the Sun. Based on previous observations of such events, scientists predicted it would arrive at Earth on January 10, 1997. SOHO and NASA's WIND spacecraft in interplanetary space between the Sun and the Earth confirmed the passage of a magnetic cloud 30 million miles thick and taking about 24 hours to pass through on its journey through interplanetary space. As the cloud engulfed Earth, its magnetic field and a trailing burst of plasma 30 times denser than the normal solar wind generated a "One-Two Punch" that compressed the front of the magnetosphere (the magnetic bubble that shields Earth from the energetic particles spewn from the Sun) inside geosynchronous orbit at 6.6 Earth radii (normally it lies about 10 Earth radii away) and resulted in intense geomagnetic activity. Preliminary estimates suggest that at the height of the event the electrical power dissipated in the aurora (both Northern and Southern Hemispheres) was about 1400 Gigawatts, almost double the electrical power generating capacity of the United States (approximately 700 Gigawatts).

SOHO and WIND in-situ observations reveal a magnetic cloud is headed toward Earth.

The ISTP science teams are thus trying to assemble the anatomy of this event as it evolved from start to finish. This includes its three-dimensional structure and evolution as it influenced the magnetosphere. A theoretical effort is also underway to help fill in observational gaps. Fortunately, the data cover the event fairly thoroughly and can readily be used to gauge the ability of theoretical or numerical models to "predict" the effect of events like this one. The results will be available to agencies that are interested in directing technical investigations regarding possible reported effects on communications systems and geosynchronous spacecraft.

Auroral activity resulting from magnetoshperic compression.

Auroral activity resulting from magetospheric compression.

A snapshot from the computer simulation of the event showing the (log) density pattern and volume dominated by the Earth's magnetic field.

An event home page has been set up on the World Wide Web to disseminate information on the event and to provide access to the available data. The event page is accessible at http://www-istp.gsfc.nasa.gov/istp/cloud_jan97/event.html

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Miranda Beall, beall@nssdca.gsfc.nasa.gov, (301) 286-0162
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.

Erin D. Gardner, gardner@nssdca.gsfc.nasa.gov, (301) 286-0163
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.



NASA home page GSFC home page GSFC organizational page

Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 24 MAR 1997 [EDG]