Coronal Mass Ejections


** Coronal Mass Ejections **

/Click on the images to see a bigger picture./

Some of the most dramatic space weather effects occur in association with
eruptions of material from the solar atmosphere into interplanetary space.
These eruptions are known as coronal mass ejections, or CMEs. A large CME
can contain 10.0E16 grams (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. The coronal image below shows the
release of a CME at the Sun.

The event occurring here is on the side of the Sun – or the limb – which
means that it will not affect us here on Earth. Sometimes, however, CMEs
occur on the front side of the Sun in a location directly in front of
Earth. These events appear to be very different when viewed from Earth.
Instead of looking like a "bubble" of plasma, they form a circle of bright
light around the Sun. This light is much dimmer than the Sun itself which
is why you need to put a disk in front of the disk of the Sun in order to
see what goes on around it. An example of such a "halo" event is shown in
the picture below.

Near solar activity maximum, the sun produces about 3 CMEs every day,
whereas near solar minimum it produces only about 1 CME every 5 days. 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.

CMEs are sometimes associated


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