HAO Colloquium - Ilya Usoskin, Univ. of Oulu, Finland

Extreme solar events: What can we expect of the Sun?

Strong eruptive events can sporadically take place on the Sun, leading in particular to the so-called solar particle storms, accompanied by very intense fluxes of solar energetic particles (SEPs). Such events, while being unnoticeable several decades ago, form a serious issue for Space Weather nowadays and pose deadly hazards for technological devices and even human lives outside the protective Earth's atmosphere and magnetosphere. Such events have been studied for nearly 70 years, with the strongest directly observed solar particle storm occurring on 23-Feb-1956 when a ~5000 % enhancement over the galactic cosmic-ray background was recorded on the ground. If such event occurred today, it would have strong technological consequences. But can even stronger storms appear? How often? What could be the "worst case scenario''? The era of direct measurements of SEP events by space-borne detectors covers 40-50 years, and by ground-based instruments about 70 years, which is too short to answer these questions. An overview of different indirect method is presented here with a search for extreme SEP events, including cosmogenic isotope (14C, 10Be, 36Cl) in terrestrial archives and lunar rocks, as well as an extensive statistic of the superflares on sun-like stars.

Considering all data in their diversity and recent achievements in this field, it is argued that the event of 775 AD may serve as the worst case scenario of an extreme solar particle storm, and that we do not expect much stronger events on the megayear timescale.

Date and time: 
Wednesday, July 17, 2019 - 2:00pm to 3:00pm