Sunspots begin as small dark areas known as pores.
These pores develop into full-fledged spots in a few
days, with maximum development occurring in about 1
to 2 weeks. When sunspots decay the spot shrinks in
size and its magnetic field also decreases in size. This
life cycle may consist of a few days for small spots to
near 100 days for larger groups. The larger spots
normally measure about 94,500 miles (120,000 kin)
across. Sunspots appear to have cyclic variations in
intensity, varying through a period of about 8 to 17
years. Variation in number and size occurs throughout
the sunspot cycle. As a cycle commences, a few spots
are observed at high latitudes of both solar
hemispheres, and the spots increase in size and number.
They gradually drift equatorward as the cycle
progresses, and the intensity of the spots reach a
maximum in about 4 years. After this period, decay sets
in and near the end of the cycle only a few spots are left
in the lower latitudes (5° to 10°).
Plages are large irregular bright patches that
surround sunspot groups. (See fig. 1-2). They normally
appear in conjunction with solar prominences or
filaments and may be systematically arranged in radial
or spiral patterns. Plages are features of the lower
chromosphere and often completely or partially
obscure an underlying sunspot.
Solar flares are perhaps the most spectacular of the
eruptive features associated with solar activity. (See fig.
1-2). They look like flecks of light that suddenly appear
near activity centers and come on instantaneously as
though a switch were thrown. They rise sharply to peak
brightness in a few minutes, then decline more
gradually. The number of flares may increase rapidly
over an area of activity. Small flare-like brightenings
are always in progress during the more active phase of
activity centers. In some instances flares may take the
form of prominences, violently ejecting material into
the solar atmosphere and breaking into smaller
high-speed blobs or clots. Flare activity appears to vary
widely between solar activity centers. The greatest flare
productivity seems to be during the week or 10 days
when sunspot activity is at its maximum.
brightness. In general, the higher the importance
classification, the stronger the geophysical effects.
Some phenomena associated with solar flares have
immediate effects; others have delayed effects (15
minutes to 72 hours after flare).
Solar flare activity produces significant disruptions
and phenomena within Earths atmosphere. During
solar flare activity, solar particle streams (solar winds)
are emitted and often intercept Earth. These solar
particles are composed of electromagnetic radiation,
which interacts with Earths ionosphere. This results in
(electrically charging neutral particles), photo chemical
changes (absorption of radiation), atmospheric heating,
electrically charged particle motions, and an influx of
radiation in a variety of wavelengths and frequencies
which include radio and radar frequencies.
Some of the resulting phenomena include the
detection. This is due to ionization, incoming radio
waves, and the motion of charged particles. Satellite
orbits can be affected by the atmospheric heating and
satellite transmissions may be affected by all of the
disturbances like the aurora borealis and aurora
electrically charged particles within the ionosphere.
Of the nine planets in our solar system, Earth is the
third nearest to (or from) the Sun. Earth varies in
distance from the Sun during the year. The Sun is 94
million miles (150,400,000 km) in summer and 91
million miles (145,600,000 km) in winter.
Earth is subject to four motions in its movement
through space: rotation about its axis, revolution around
the Sun, processional motion (a slow conical movement
or wobble) of the axis, and the solar motion (the
movement of the whole solar system with space). Of
the four motions affecting Earth, only two are of any
importance to meteorology.