What does the 304A solar parameter measure?

  1. The ratio of x-ray flux to radio flux, correlated to sunspot number
  2. UV emissions at 304 angstroms, correlated to the solar flux index
  3. The solar wind velocity at 304 degrees from the solar equator, correlated to solar activity
  4. The solar emission at 304 GHz, correlated to x-ray flare levels