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SPACE SCIENCES

Cosmic radiation decreases as

Solar Cycle 25 takes off

ew data from cosmic ray balloons show that Solar Cycle 25 sun’s magnetic shield, and atmospheric radiation is dropping.
is having an effect on Earth’s atmosphere. Radiation levels in Every time the students launch a balloon, they have to recover
Nthe air above our heads is decreasing as the new solar cycle the payload to get the results--often from rugged mountain peaks
gains strength. Spaceweather.com and the students of Earth to Sky and remote deserts. There’s a little blood, sweat and/or tears in
Calculus have been monitoring the situation for more than six years. each data point. For many of them, this is the best part of the
programme. Their adventures have resulted in an uninterrupted
record of in situ atmospheric radiation measurements now straddling
two solar cycles.
Cosmic rays are a surprisingly “down to Earth” form of space
weather. They can seed clouds, trigger lightning and penetrate
commercial airplanes. According to a study from the Harvard T.H.
Chan school of public health, crews of aircraft have higher rates of
cancer than the general population. The researchers listed cosmic
rays, irregular sleep habits and chemical contaminants as leading
risk factors. Somewhat more controversial studies link cosmic rays
with cardiac arrhythmias and sudden cardiac death.
En route to the stratosphere, our sensors also pass through
aviation altitudes:

The latest plot shows cosmic rays in the stratosphere, measured by
radiation sensors they launch almost once a week from the Sierra
Nevada mountains in California. Recent flights confirm that radiation
levels are decreasing for the first time since 2015.
Cosmic rays come from deep space – mostly from supernova
explosions. To reach the inner solar system, they must fight their way
through the sun’s protective magnetic field. Once cosmic rays reach
Earth, they crash into the top of our atmosphere, creating a spray of
secondary radiation, which is measured using high-altitude balloons.

In this plot, dose rates are expressed as multiples of sea level. For
instance, boarding a plane flying at 25 000 feet exposes passengers
to dose rates ~10x higher than sea level. At 40 000 feet, the
multiplier is closer to 50x. The higher you fly, the more radiation you
will absorb.
The radiation sensors onboard the helium balloons detect X-rays
and gamma-rays in the energy range 10 keV to 20 MeV. These
energies span the range of medical X-ray machines and airport
security scanners.
Data points in the first graph (“Stratospheric Radiation”)
The plot clearly shows the end of Solar Cycle 24. correspond to the peak of the Regener-Pfotzer maximum, which
Atmospheric radiation increased during 2015-2019 because lies about 67,000 feet above central California. When cosmic rays
then Solar Cycle 24 was decaying. The sun’s magnetic field became crash into Earth’s atmosphere, they produce a spray of secondary
weak and uncomplicated; cosmic rays from deep space found it particles that is most intense at the entrance to the stratosphere.
easier to reach earth. The highest measurements towards the end of Physicists Eric Regener and Georg Pfotzer discovered the
2019 correspond with NOAA’s official date of Solar Minimum. Now maximum using balloons in the 1930s and this is what is being
the sun is waking up again. New Solar Cycle 25 is strengthening the measured today. n

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