For the past month, solar activity has been low. The last big burst of solar activity happened on May 5th when an X2-class solar flare erupted from the sun's eastern limb. Since then ... quiet. To investigate the effect of low solar activity on the atmosphere, and the students of Earth to Sky Calculus have been launching helium balloons at ~weekly intervals. Equipped with X-ray and gamma-ray sensors, the balloons measure ionizing radiation all the way from ground level to the stratosphere. Here are the results:
Increased Cosmic Rays
During the past month of low solar activity, ionizing radiation in the stratosphere has increased by 10%. This may seem counterintuitive, but there is a simple explanation: The radiation we measure is dominated by cosmic rays--a mix of subatomic particles, X-rays and gamma-rays that come from outside the solar system. Explosions on the sun (especially CMEs) tend to push these cosmic rays away from Earth. During the past month, however, there have been relatively few CMEs. Fewer CMEs means more cosmic rays. Yin-yang.

Cosmic rays are an important form of space weather. They matter to anyone who steps foot on an airplane. According to NASA, a 100,000 mile frequent flier will absorb a dose of radiation equivalent to 10 chest X-rays--all from cosmic rays. Cosmic rays have also been linked to cloud cover, lightning, and they may play some role in climate change.

If the sun remains quiet, cosmic rays could increase even more. Stay tuned for updates from the stratosphere.