RADIATION STORM: A low-level radiation storm is underway as solar protons swarm around our planet. Ranked S1 on NOAA space weather scales, the storm poses no serious threat to astronauts or satellites. Nevertheless it is a nuisance. Minor radiation storms can cause occasional reboots of computers onboard spacecraft and add “snow” to spacecraft imaging systems. This SOHO coronagraph image of the sun, taken during the early hours of July 20th, is a good example:

Each of the speckles in the image (a handful are circled) are caused by protons hitting the spacecraft’s CCD camera. During minor storms it is possible to see through this kind of snow. During severe storms, such images become practically opaque.

The protons were accelerated toward Earth by an M7-class solar flare on July 19th. Although the blast site (sunspot AR1520) was on the farside of the sun, the protons were able to reach Earth anyway, guided toward our planet by backward-spiralling lines of magnetic force.

from:    spaceweather.com