Coronal mass ejections occur at a rate of a few times a week to
several times per day, depending on how active the Sun may be.
And because of the size of the plasma clouds they produce, the
odds say Earth is going to get hit by a CME from time to time.
Fortunately, our planet is protected from the harmful effects of
the radiation and hot plasma by our atmosphere and by an invisible
magnetic shell known as the magnetosphere. Produced as a result
of Earth's own magnetic field, the magnetosphere shields us from
most of the Sun's plasma by deflecting it into space.
But some energetic particles do enter the magnetosphere from time
to time, funneling in near the North and South Poles, where the
magnetic field is weakest and the magnetosphere is partially open
to space. The rain of plasma into our magnetosphere can induce
magnetic storms, alter Earth's magnetic field as measured on the
ground, and produce the phenomena known as auroras.
Many things can happen in the magnetosphere during a magnetic storm
because a lot of energy is being dumped into the system. When impacted
by plasma from space or even from the far reaches of the
magnetosphere, the electrons, protons, and oxygen ions of Earth's
Van Allen radiation belts become denser, hotter, and faster. Due to
their motion, these particles produce as much as a million amperes
of electrical current, a jolt of power that can decrease the
strength of Earth's magnetic field. Some of the current flows along
Earth's magnetic field lines and into the upper atmosphere. The
passage of electric current through the upper atmosphere and the
loss of electrons and protons from the magnetosphere can cause the
atmosphere to warm and expand, increasing the density
Finally, some of the excited particles in the radiation belts can
plunge into the upper atmosphere, where they collide with oxygen
and nitrogen. These collisions-which usually occur between 40 and
200 miles above ground-cause the oxygen and nitrogen to become
electrically excited and to emit light (fluorescent lights and
televisions work in much the same way). The result is a dazzling
dance of green, blue, white, and red light in the night sky, also
known as aurora borealis and aurora australis ("northern and
southern lights"). Auroras can appear as colorful, wispy curtains
of light ruffling in the night sky, or sometimes as diffuse,
flickering bands. Either way, they tell us that something electric
is happening in the space around Earth.
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