Atmospheric radiation and Earth to Sky Calculus have just released a new batch of cosmic ray balloon data. Their conclusion: Atmospheric radiation is near a 5-year high. This plot shows a 15% increase since the monitoring program began in 2015.

What's happening up there? The answer is "Solar Minimum." During the nadir of the 11-year solar cycle, the sun's magnetic field weakens, allowing extra cosmic rays from deep space to penetrate the solar system. These cosmic rays are hitting Earth's atmosphere, creating an intensifying spray of secondary cosmic rays that we detect with sensors onboard our balloons.

The graph, above, shows that Solar Minimum is underway. Recently, NASA and NOAA announced the onset of a new (but still feeble) solar cycle. Eventually, Solar Cycle 25 will bend the cosmic ray curve down again. But when?