At www.spaceweather.com September 18th .... on the 12th a CME hit Earth's magnetic field igniting an intense geomagnetic storm - and providing England with a week of summer temperatures. Students launched a helium Balloon into the stratosphere, expecting to measure lots more radiation than normal. Instead, them measured less - a lot less. Why?
Well, it seems that when the CME swept past the Earth it gathered up a lot of cosmic rays that normally occupy the upper atmosphere - sweeping them away. This process was first discovered in the 20th century by Scott Forbush.