April 23, 2019: Ten years ago, NASA reported a “perfect storm of cosmic rays.” During the year 2009, radiation peppering Earth from deep space reached a 50-year high, registering levels never before seen during the Space Age.
It’s about to happen again.
Ground-based neutron monitors and high-altitude cosmic ray balloons are registering a new increase in cosmic rays. The Oulu neutron monitor in Finland, which has been making measurements since 1964, reports levels in April 2019 only percentage points below the Space Age maximum of 2009:
What’s going on? The answer is “Solar Minimum.” During the low phase of the 11-year solar cycle, the sun’s magnetic field and solar wind weaken. Cosmic rays find it easier to penetrate the inner solar system. In 2009, the sun experienced the deepest solar minimum in a century. Cosmic rays reaching Earth naturally surged.
Ten years later, solar minimum is back with renewed weakening of the sun’s magnetic field and the solar wind. Again, it’s a “perfect storm.” A panel of experts led by NOAA and NASA recently predicted that the current minimum would reach a nadir in late 2019 or 2020, likely matching the record-setting minimum of 2009. If they’re right, cosmic rays will continue to increase, with a new record possible in the near future.
Cosmic rays cause “air showers” of secondary particles when they hit Earth’s atmosphere. Indeed, this is what neutron monitors and cosmic ray balloons are measuring–the secondary spray of cosmic rays that rains down on Earth.
This spray is of special interest to air travelers. Secondary cosmic rays penetrate the hulls of commercial aircraft, dosing passengers with the whole body equivalent of a dental X-ray even on ordinary mid-latitude flights across the USA. International travelers receive even greater doses.
The International Commission on Radiological Protection has classified pilots as occupational radiation workers because of accumulated cosmic ray doses they receive while flying. Moreover, a recent study by researchers at the Harvard School of Public Health shows that flight attendants face an elevated risk of cancer compared to members of the general population. They listed cosmic rays as one of several risk factors.