Atmospheric impact of the strongest known solar particle storm assessed

An exceptional solar particle storm, the strongest during the last ten thousands of years, is able to perturb the polar stratosphere for at least one year and lead to winter temperature rises up to several degrees centigrade in the Northern Hemisphere. Knowing the effects of a worst-case scenario of such a hazardous event will help in risk evaluation for solar particle storms.

Solar particle storms are sporadic events caused by powerful eruptions on the Sun that may affect Earth in different ways. In particular, they lead to failure and disruptions of modern navigation and communication technologies and to radiation hazards for astronauts and transpolar jet crews and passengers. Hundreds and thousands of such events have been detected during the last decades, and impacts of some of them have been assessed as hazardous. But what could be the worst case scenario? What kind of event can we expect from our Sun on a bad day?

An international team combining 11 groups from six countries (Australia, Finland, Italy, Japan, Russia, Switzerland), led by scientists from Switzerland and Finland, has studied the atmospheric effect of the strongest known solar particle storm which occurred in the late Spring or early Autumn of 774 AD, more than 1200 years ago.

No direct measurements are available for that event, of course. Using data from cosmogenic beryllium-10 measured in polar (Arctic and Antarctic) ice cores and radiocarbon (carbon-14) in tree rings, the team has demonstrated that the extreme solar particle storm of 774 AD may reliably serve as the worst case scenario for the solar radiation hazard on the time scale of tens of thousands of years. This sets a strong observational constraint on the risk evaluation of severe solar particle storms.

Using a multi-proxy reconstruction, the team has evaluated the possible atmospheric and climatic impact of such a severe event and showed that it is able to perturb the polar stratosphere for at least one year. This will lead to regional changes in the surface temperature up to several degrees centigrade during Northern Hemisphere winters, which is a conservative upper limit for the immediate effect of solar particle storms.

The University of Oulu was represented by PhD student Eleanna Asvetsari and professor Ilya Usoskin, working in the frameworks of the ReSoLVE Centre of Excellence, who performed detailed state-of-the-art modelling of the cosmogenic radionuclide production and transport during the extreme event in the conditions corresponding to 775 AD.

The research was published in the Scientific Reports series of the Nature Group on 28th of March 2017.

Research report:

Sukhodolov, T., I.G. Usoskin, E. Rozanov, E. Asvestari, W. Ball, M.A.J. Curran, H. Fischer, G. Kovaltsov, F. Miyake, T. Peter, C. Plummer, M. Severi, W. Schmutz, R. T, Atmospheric impacts of the strongest known solar particle storm of 775 AD, Sci. Rep., 7, 45257 2017 (doi: 10.1038/srep45257)

Photo: JAXA/NASA

Last updated: 6.4.2017