Are solar / geomagnetic storms real risks for commercial aviation? Background

Solar storms/flares are solar events sending particles in space that are potentially dangerous on Earth. From Wikipedia:


  Solar flares strongly influence the local space weather in the
  vicinity of the Earth. They can produce streams of highly energetic
  particles in the solar wind, known as a solar proton event. These
  particles can impact the Earth's magnetosphere (see main article at
  geomagnetic storm), and present radiation hazards to spacecraft and
  astronauts. Additionally, massive solar flares are sometimes
  accompanied by coronal mass ejections (CMEs) which can trigger
  geomagnetic storms that have been known to disable satellites and
  knock out terrestrial electric power grids for extended periods of
  time.



Source

They are rated by the US NOAA on a scale from 1 to 5. For instance, level 3 events occur about once a year:


  S3 (Strong) - Biological: radiation hazard avoidance recommended
  astronauts on EVA. Passengers and crew in commercial jets at high
  latitudes may receive radiation equivalent to approximately 1 chest
  x-ray.


There are also geomagnetic storms listed on the same page.

Question

Is this a real risk for commercial aviation, if so how do airlines treat this risks on affected routes, e.g.:


How are airlines informed?
Are pilot-in-command informed and allowed to veto a flight?
What do they do regarding exposed crews and passengers?
A pilot in command can always veto, scrub, or divert a flight. Per the Federal Aviation Regulations FAR 91.3(a), "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft." This applies to airline operations (air carriers, FAR Part 121), air taxis and charters (FAR Part 135), and general aviation (FAR Part 91) operations.

A much bigger issue than than the radiation exposure for the people will be the atmospheric effects of the radiation, and how the radiation affects, e.g., satellite navigation. A very strong solar flare can require shutting down some on-orbit satellites to avoid damage—including navigation satellites, such as GPS. A very strong solar flare can ionize the atmosphere to the point it interferes with communications, especially in the HF band used for transoceanic communications.