2001-10-26 | SCIENCE
'Tis the Season for Auroras
Solar activity does not depend
on the Earth's seasons, yet geomagnetic storms are much more common around the
time of the equinoxes—that
is, early Autumn and Spring. Geomagnetic storms erupt when bursts of magnetized
gas from the Sun (called coronal
mass ejections or CMEs) or gusts of solar
wind collide with Earth's magnetic field (the magnetosphere).
Electrons and protons that are normally trapped
in the magnetosphere are knocked loose by the blasts from the Sun, and rain
down to the Earth, creating brilliant auroras.
Although auroras are normally only visible near the poles, during Spring and Autumn
they can spread
all the way to the middle latitudes.
Where
Earth's and the Sun's magnetic fields meet, Earth's magnetic field is pointing
north. If the Sun's
magnetic field happens to be pointing south, it can partially cancel out
Earth's. This north-south alignment is most common during Spring and Autumn.
It accounts for much of the seasonal increase in auroras, but not nearly all.
Scientists are still trying to determine what other factors are at work.
A magnetosphere may be necessary
for a planet to support life. Earth's magnetosphere protects Earth life
from harmful radiation from the solar wind and CMEs. Solar storms have recently
been shown to deplete
Earth's ozone layer temporarily. When Mars
lost its own magnetosphere, the solar
wind eroded much of the planet's atmosphere.
More on this story
Full text of original item
from NASA, Oct 26, 2001
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