Cradle-to-Grave During Solar Minimum:
The Space Weather Event of January 1997
Contents:
- Cradle-to-Grave Observations
- Unusual at Solar Minimum
- Quotes and Anecdotes
- Chronology
- Useful Sources
- Images
Cradle-to-Grave Observations:
The exceptional observations made during the space weather event of January 1997 were initiated mainly by chance. At a workshop on January 7 at NASA's Goddard Space Flight Center, scientists reviewed images of solar activity taken the previous day. The segment from the Solar and Heliospheric Observatory's Large-Angle Spectrometric Coronagraph (an instrument that blocks the bright disk of the Sun, making visible the faint corona around it) happened to show a halo-like feature around the Sun: the front of a huge bubble of plasma known as a coronal mass ejection, headed toward Earth. The halo was first noticed in images from 17:30 UT (Univeral Time) on January 6 and was tracked in the coronagraphs for the next nine hours as it moved out into space. The scientists predicted that Earth would be affected in about three days, the time it would take for the cloud to travel from the Sun. Observatories in space and on the ground were placed on alert.
On January 8, the first signs of the plasma cloud's approach appeared in data from the Wind satellite's WAVES instrument. The instrument detected Type II radio bursts coming from the cloud and decreasing in frequency as the cloud moved closer to Earth. Using this information, scientists could track it through space. Once the bubble of plasma came within a million miles of Earth, it could affect its first satellite directly. SOHO saw the speed and density of the solar wind jump up at 00:10 UT on January 10; around 04:00 UT, the speed rose again to 520 km/sec (just over a million miles an hour), while the density fell. Wind detected the magnetic cloud a distance of 70 Earth radii upstream from Earth at 04:40 UT; eighteen minutes later, it was at Earth.
Auroral activity began suddenly around the poles as more than a million total amps of current flowed through the ionosphere. The northern lights were seen shining above Alaska, Canada, and Scandinavia, while communications in Antarctica were disrupted and flights grounded because of the progressing magnetic storm. The 30-million-mile-wide cloud then took an entire day to pass Earth. Just when things were calming down, early on January 11, a very high-density region at the end of the cloud smacked the planetary magnetic field with a huge pressure pulse, energizing radiation belts around the equator even further. After that last blow from space, the disturbance at Earth cooled off and was essentially over by the end of the day.
The importance of the January 1997 space weather event lies in the wealth of data collected. From the first identification of the cloud at the January 7 workshop, the International Solar-Terrestrial Physics (ISTP) program coordinated observations of the event. ISTP's four main satellites watched the passage of the storm along with at least ten other satellites. ISTP satellites SOHO, Wind, and Geotail were directly on line with the cloud at the time, giving an excellent view. About fifteen radar networks and magnetometer chains on the ground also contributed data, with four ISTP theory centers providing modeling and interpretation. The ISTP program allowed, for the first time, collection and coordination of these data so a picture of the magnetic storm could be drawn from its inception to its end -- from cradle to grave.
A few unusual characteristics came along with the event, however. The boundary of Earth's
magnetic field area, the magnetopause, normally comfortably outside the orbit of all
geosynchronous satellites, was rammed in toward Earth by the pressure pulse at the end
of the cloud. Suddenly, a few geosynchronous satellites found themselves outside the
protective shell of the magnetosphere. This magnetopause-crossing was the first of its
kind to occur while the interplanetary magnetic field was pointed northward. (Typically,
only a southward IMF allows dramatic effects to occur at Earth.)
Also, shortly after the pressure pulse pushed back the magnetopause and excited electrons
in the radiation belts, AT&T's Telstar 401 communications satellite went silent. At 11:15 UT
on January 11, telemetry and communications links failed, cutting off ABC, Fox, and PBS
signals. The $200 million spacecraft, launched in 1993, became space junk eight years
before it should have. The day before, another
satellite had experienced voltages twice as high as the normal level,
warning that the electronic systems of satellites could be
significantly effected. Solar origins of the failure could not be
confirmed (both because inspection of the damage was impossible and for insurance reasons),
but the coincidence of the storm and the failure were enough for some scientists to
feel certain. Even though the intensity of the storm was only average, therefore,
its effect on the general TV-watching public could have been great.
Quotes and Anecdotes:
Unusual at Solar Minimum:
The January 1997 event was not the biggest storm ever. In fact, it was a fairly average
disturbance, appropriate to the solar minimum period in which it fell. The auroral displays
caused by the magnetic storm (although pronounced in images from Polar, below)
were barely more widespread than normal. The Dst index, an index of geomagnetic activity based on
the strength of Earth's magnetic field near the equator, fell only to -84 nT, a respectable but
not striking minimum for a magnetic storm.
Chronology (all times Universal Time):
[January 6, 1997]
15:50 -- CME leaves solar surface (estimated)
17:30 -- First signs of halo CME detected by SOHO/LASCO
18:50 -- Full CME seen on SOHO/LASCO inner coronagraph
[January 8, 1997]
02:00 -- Type II radio bursts first detected by Wind/WAVES
[January 10, 1997]
00:10 -- Solar wind speed and density rise (SOHO/CELIAS)
00:50 -- Wind detects shock
01:00 -- Diffuse aurora seen in Alaska, Canada
04:30 -- Solar wind speed rises again; density falls (SOHO/CELIAS)
04:40 -- Magnetic cloud arrives at Wind
04:58 -- Magnetic cloud arrives at Earth
[January 11, 1997]
01:00 -- High density solar wind compresses magnetosphere
01:00 -- Radio bursts end
11:15 -- Telstar 401 experiences abrupt failure of telemetry
Useful Sources:
Images from the Event:
USA Today's story on the cradle-to-grave observations
LASCO C3 four-panel image of the halo CME
Images of the aurora from the Polar satellite
Sequence of VIS images showing the progression of the aurora
VIS images showing sudden storm commencement
