This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Radiation from space is constantly entering Earth's atmosphere, but how much of it reaches the altitudes used by commercial aircraft depends not only on height and location, but also on the activity of the sun. A new study based on high-altitude balloon measurements over southern Israel has mapped these changes through the atmosphere and found that radiation levels at aviation altitudes rise as solar activity falls.
The study, published in the Journal of Geophysical Research: Atmospheres, was conducted by Dr. Roy Yaniv of Hebrew University of Jerusalem and Sheba Medical Center; Professor Yoav Yair of Reichman University; and Professor Colin Price of Tel Aviv University. The researchers analyzed measurements collected during six balloon launches from southern Israel between 2014 and 2016.
The balloons, equipped with radiation sensors, climbed as high as approximately 35 kilometers (22 miles), allowing the team to understand how atmospheric ionization and radiation changed from near the ground to well above the altitudes used by passenger aircraft. The measurements revealed a clear vertical pattern. Radiation increased as the balloons climbed, reaching its highest levels at around 17 to 20 km (11 to 12 miles) above Earth before declining again.
This peak, known as the Regener-Pfotzer maximum, is created as high-energy cosmic rays entering the atmosphere collide with atmospheric particles and produce cascades of secondary particles. At approximately 10 km (6 miles), around the altitude at which commercial aircraft typically cruise, the researchers measured gamma-equivalent radiation dose rates of roughly 0.9 to 1.3 microsieverts per hour. The relatively low levels measured over Israel compared with some higher-latitude regions are consistent with the stronger geomagnetic shielding found in the Eastern Mediterranean.
But altitude was only part of the story. The team also found that radiation levels changed during the solar cycle. When solar activity is high, the sun's magnetic influence helps shield the solar system from harmful galactic cosmic rays.
During periods of lower solar activity, more of these energetic particles can reach Earth's atmosphere. Accordingly, the researchers observed higher radiation levels when solar activity was lower. The measured relationship showed a negative correlation of r = -0.71, although the researchers stress that the limited number of observations means that this correlation should be considered indicative rather than statistically definitive.
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