Sun flare activity may solve unknown source of helium-3 in the atmosphere

Helium abundance measurements in the atmosphere suggest a supply of crustal 4He from natural gas extraction since the beginning of the 20th century. However, the 3He/ 4He ratio of air appears near constant, which calls for an unknown source of 3He to compensate for the contribution of anthropogenic 4He to the atmosphere. Knowing the origin and cycle of 3He in the atmosphere is important, being also an important resource in nuclear fusion reactors and for cryogenic applications. Here, we report 3He/4He variations measured during the massive X9.3 solar flare event of September 6th 2017 in Ny-angstrom lesund, Svalbard islands, near the North Pole. The solar wind was expected to reach the Earth on September 8th. A total of five samples, collected immediately after the solar flare event, showed an excess of 3He, up to 5.5 +/- 1.7 %o (delta 3He), compared to the terrestrial atmospheric isotopic value. If the solar wind, enhanced by solar flares, was fed into the atmosphere by auroral precipitation, it would increase the polar atmospheric helium isotope ratio. The helium would then be diluted by diffusion and the excess 3He would rapidly disappear. Thus, 3He excess supplied by these events may keep the atmospheric 3He/4He constant.