On the contrary to popular belief, solar storms caused by solar flares and coronal mass ejections tend to decrease the intensity and the amount of cosmic radiation received on the Earth’s surface. This phenomenon, also known as the Forbush decrease, can last for days or even weeks, as recorded by NASA. The only humans exposed to higher doses of radiation after a coronal mass ejection can be astronauts outside their space ship, like those taking a spacewalk. Aside from the totally different harmful ground effects of major solar storms caused by fluctuations in the Earth’s magnetic field and mainly affecting electrical power grids, this is another very important reason why NASA and other similar worldwide institutions keep constantly and carefully monitoring solar activity, particularly before scheduled extravehicular activities.
Everyone on Earth and even astronauts inside a space station or a rocket actually get a lower than usual dose of radiation during an average solar storm. The reason for this is that solar storms suppress the more dangerous, powerful and deeper penetrating cosmic rays.
This has to do with the nature and different energy levels (speed) of the particles hitting our planet: solar storms release high-energy protons which are however still considered as low-energy cosmic rays and as such easily stopped by the Earth’s magnetic field, ionosphere and the molecules of the atmospheric gases and moisture on Earth, or by a hull of a space station, airplane or satellite in orbit. On the other hand, supercharged particles of the very high energy cosmic radiation from outside the Solar System penetrate much deeper through the Earth’s shields mentioned above and some of them reach the surface.
But when a strong solar wind is present, it actually forms a protective surrounding flow of lower energy particles that acts like a shield, slowing down the far more powerful and more dangerous cosmic rays before they hit Earth. Imagine the solar wind particles as if they were rain and cosmic rays as much faster and heavier hail, falling under different angles so that the faster and more dangerous hail melts and slows down while mixing with slower but denser rain showers, and as a result the ice doesn’t rip through the umbrella (Earth’s shields).
So just like you don’t have to worry much about radiation from cell phones, there’s no need to wear a tinfoil hat during a solar storm, because you may be receiving less radiation than usual. However, if it’s a major one you should be concerned about your electrical appliances and other devices connected to the power grid, because major solar storms can cause blackouts and problems with power grids through variations in the Earth’s magnetic field.
Read more about the shielding effect of solar storms at:
Who’s Afraid of a Solar Flare?
By Dr. Tony Philips of NASA
The Forbush Decrease on Wikipedia