Spectra of high energy electron precipitation and atmospheric ionization rates retrieval from balloon measurements.

The bremsstrahlung from high and relativistic energy electron precipitation (HEEP) measured with balloon based instruments provides information on energy spectra and fluence of the precipitating energetic electrons allowing calculations of the atmospheric ionization. HEEP from the outer radiation belt at the subauroral region causes an increase in the ionization rates down to about 20 km altitudes. We study the variability in the ionization rate using the balloon observations of secondary bremsstrahlung initiated by HEEP.

Author Correction: Solar superstorm of AD 774 recorded subannually by Arctic tree rings.

The authors became aware of a mistake in the data displayed in Fig. 1 and Supplementary Table 2 of the original version of the Article. Specifically, the C production values were printed out in the code before the conversion between the omnidirectional fluence and the flux.

Solar superstorm of AD 774 recorded subannually by Arctic tree rings.

Recently, a rapid increase in radiocarbon (C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete.

Atmospheric impacts of the strongest known solar particle storm of 775 AD.

Sporadic solar energetic particle (SEP) events affect the Earth's atmosphere and environment, in particular leading to depletion of the protective ozone layer in the Earth's atmosphere, and pose potential technological and even life hazards. The greatest SEP storm known for the last 11 millennia (the Holocene) occurred in 774-775 AD, serving as a likely worst-case scenario being 40-50 times stronger than any directly observed one. Here we present a systematic analysis of the impact such an extreme event can have on the Earth's atmosphere.