The level of auroral activity is directly related to the level of solar
activity. The solar wind and other solar activities blast charged particles
away from the sun. The interaction between these charged particles and
Earth's magnetic field produces the aurora.
The solar connection
The surface of the sun is not a quiet place, it
seethes with burning gases and massive explosions that blow millions of
tons of charged particles into space.
Loops and arches in the corona
are giant fountains of super-
heated gas
click to see larger image
Solar activity affecting the aurora:
Solar Wind:
the streams of charged particles that produce the aurora come from the
corona, the outermost layer of the sun's atmosphere. The corona is exceedingly
hot, measuring more than one million degrees. The high temperature causes
hydrogen atoms to split into protons and electrons. The resulting gas
of charged particles is called plasma, which is electrically conductive.
The solar plasma is so hot that it breaks free of the sun's gravitational
force and blows away from the surface in all directions. The movement
of this plasma is called solar wind. The intensity of the solar wind and
the magnetic field carried by it change constantly. When the solar wind
blows stronger, we see more active and brighter aurora on Earth.
Helpful links:
Space
Weather Guide
from NASA's Sun-Earth
Connection Education Forum
"Living
in the atmosphere
of the Sun"
Big
Bear solar
observatory website
click to watch a movie of
a comet and a CME
(420 kb MPEG)
Coronal mass ejections are, as the name implies, massive explosions of the corona. Made of plasma and threaded with the sun's magnetic field lines, coronal mass ejections are responsible for gusts of solar wind. They can be very damaging if they collide with Earth. They can disrupt radio communications, damage satellites, and even be hazardous to astronauts if they are outside the spacecraft.
Sunspots
click to see larger image
Sunspots appear as small dark dots on the sun's surface. They appear dark because they are cooler than the surrounding surface. Intense explosions often occur around sunspots which can cause "gusts" of solar wind.
Sunspot cycle: The number of sunspots on the sun's surface changes on a fairly regular cycle, which scientists refer to as the sun's 11-year cycle variation. Sunspot activity, and hence auroral activity, tends to peak every 11 years. This peak is called the Solar Maximum. The last solar maximum was in 2001, the next is expected around 2012. The chances of seeing the aurora at lower latitudes is affected by the sunspot cycle, but chances at higher latitudes are not dependent as the auroral oval is normally present.
Sunspot cycle
click to see larger image
Coronal holes: strong solar wind can also blow out unexpectedly from a quiet region of the sun. While examining the x-ray images of the solar corona, scientists discovered large dark holes referred to as coronal holes. The coronal hole, which tends to develop after the sunspot cycle peaks, can last more than 12 months. Because the sun completes one rotation in 27 days (Earth completes one rotation in 24 hours), the solar wind from the coronal hole "hits" Earth every 27 days.
Particles from a coronal hole
strike Earth every 27 days
click image to see a Flash movie (32kb)
coronal hole
click to see larger image
rotating sun movie
(2447 kb MPEG)
Increased auroral activity
When the solar wind blows strong, the auroral oval
becomes brighter and wider. In the sky, the aurora appears bright, active,
contains more colors, and can be seen further south than normal. While
a quiet aurora displays only pale green curtains, more active ones will
have a pink band at the bottom edge and exceptionally strong ones will
glow deep red at the top. As the auroral oval expands, the aurora can
be seen further south of where it normally occurs. Throughout history,
reports of the aurora appearing as a red glow in the northern sky have
been recorded in countries as far south as Japan, Mexico, Iran, and Italy.
In these cases, the viewers were observing the extensive red upper portion
of an extremely powerful aurora.
Geophysical Institute
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site last modified: August 2003 maintained by Asahi Aurora
Web Manager