Hi Erik,

We have a couple of ways now of telling if a solar storm might come to Earth. First, if there's a big flare near the center of the solar disk, it may result in a storm that reaches Earth. Also, a coronal mass ejections (CME), which is a major part of a solar storm, has a certain appearance when seen from the coronagraph on the near-Earth spacecraft SOHO. If it's headed towards Earth, it make a white ring around the Sun as seen in a SOHO coronagraph image. We call these "halo CMEs." Of course,we also now have the two twin STEREO spacecraft (see http://stereo.gsfc.nasa.gov/) with coronagraphs that can see two views of a CME simultaneously. These spacecraft are now looking at the Sun from quite a different viewpoint than SOHO..And using these spacecraft, we can determined if the CME is going to impact Earth.

Paulett