Press Release

Fireworks Display on the Sun

By SpaceRef Editor
June 7, 2000
Filed under

For the first time during this solar cycle, the Sun put up a spectacular fireworks
display on June 6 with two X-class flares going off in close succession from one and the
same active region of the Sun.

The flares were also associated with a "full halo coronal mass ejection",
which means that a huge cloud of material is ejected in the direction of the Earth,
possibly causing geomagnetic disturbances in 2-4 days.

The X-ray activity was detected by the GOES satellite from the National Oceanic and
Atmospheric Administration’s Space Environment Center (NOAA/SEC).

NOAA’s Space Environment Center and the U.S. Air Force are calling strong geomagnetic
storm levels (Category G3 on the NOAA Space Weather Scale) during June 8 – 9. These storm
levels may cause some or all effects on the following: power system grids may require
voltage corrections, false alarms may be triggered on protection devices, and high
"gas-in-oil" transformer readings may occur. Spacecraft may experience surface
charging, increased drag, and orientation problems may need correction; high-frequency
radio propagation may be intermittent; intermittent low-frequency radio navigation and
satellite navigation problems may occur; and the aurora may be seen as low as 50 degrees.
Isolated radio blackouts are expected during the period.

For more on Today’s Space Weather, visit the NOAA Space Environment Center’s web site

The first powerful X-class solar flare erupted at 1530 UT and the second occurred about
2 minutes later. Soon thereafter, coronagraphs on board the orbiting ESA/NASA Solar and
Heliospheric Observatory (SOHO) recorded a dramatic full-halo coronal mass ejection. NASA
and NOAA space weather forecasters say that the leading edge of the disturbance will
trigger geomagnetic storms — including aurora — when it passes by Earth on June 8.

The SOHO spacecraft recorded the coronal mass ejection using two of its onboard

The LASCO (Large Angle Spectrometric Coronagraph) is able to take images of the solar
corona by blocking the light coming directly from the Sun with an occulter disk, creating
an artificial eclipse within the instrument itself. The position of the solar disk is
indicated in the images by the white circle. The most prominent feature of the corona are
usually the coronal streamers, those nearly radial bands that can be seen shooting off in
all directions from the Sun.

In the LASCO image, the CME appears as a bright front, particularly over the North
Pole, with trailing filamentary material. The plane-of-sky speed of the leading edge of
the halo is about 908 km/s, possibly with some deceleration in the outer part of the C3
field of view. The shadow crossing from the lower left corner to the center of the image
is the support for the occulter disk.

Images and movies of this event are available at the LASCO ftp server:

The other view is from SOHO’s EIT, or Extreme ultraviolet Imaging Telescope. EIT images
the solar atmosphere at several wavelengths, and therefore, shows solar material at
different temperatures. EIT observed the flare and filament eruption beginning at about
15:12 UT. There was also an earlier X1.1 flare and filament eruption from the same region,
that was observed by EIT at about 13:36 UT. This flare was probably associated with an
earlier CME that merged with the halo,

CMEs are responsible for some of the most dramatic space weather effects on Earth. A
large CME can contain a billion tons of matter that can be accelerated to several million
miles per hour in a spectacular explosion. Solar material streaks out through the
interplanetary medium, impacting any planets or spacecraft in its path.

Near solar activity maximum, the period we are in now, the Sun produces about 3 CMEs
every day, whereas near solar minimum it produces only about 1 CME every 5 days.

Not every CME effects the Earth. Those which erupt on the side of the Sun – or the limb
– will not affect us here on Earth. CMEs that occur on the front side of the Sun in a
location directly in front of Earth, such as the event recorded yesterday, can cause major
terresrial reslts of solar variations, including aurorae, proton events and geomagnetic
storms. They can also disrupt communications systems, navigation systems, satellites and
electrical power grids,

The faster CMEs have outward speeds of up to 2000 kilometers per second, considerably
greater than the normal solar wind speeds of about 400 kilometers per second. These
produce large shock waves in the solar wind as they plow through it.

For more information on SOHO, check out:

SpaceRef staff editor.