QUESTION:
If a solar flare from the sun was to reach the earth, what types of effects
would it have on the earth and its weather?

ANSWER from Bryan Miller on May 2, 1996:
Visible solar flares or prominences never actually reach the earth, but
we definitely feel the effects of these solar storms.  Flares produce
high energy ultraviolet and X-ray radiation which cause disturbances in
the Earth's ionosphere and make long distance radio communication more
difficult.  High levels of solar activity can heat the Earth's upper
atmosphere, causing it to expand and producing more drag on satellites
in low Earth orbit.  The flares also accelerate charged particles which
produce aurorae, or northern lights, when they get trapped by the
Earth's magnetic field.  Both the radiation and the charged particles
are dangerous to astronauts in Earth orbit.  Exposure to solar flares
can increase the risk of an astronaut to getting cancer or to having
children with birth defects.  Therefore, spacecraft and spacesuits are
designed with shielding to protect the astronauts.  Solar flares have
little, if any, effect on the Earth's weather.