Abstract
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. Using state-of-the-art cosmic ray cascade and chemistry-climate models, we successfully reproduce the observed variability of cosmogenic isotope 10Be, around 775 AD, in four ice cores from Greenland and Antarctica, thereby validating the models in the assessment of this event. We add to prior conclusions that any nitrate deposition signal from SEP events remains too weak to be detected in ice cores by showing that, even for such an extreme solar storm and sub-annual data resolution, the nitrate deposition signal is indistinguishable from the seasonal cycle. We show that such a severe event is able to perturb the polar stratosphere for at least one year, leading to regional changes in the surface temperature during northern hemisphere winters.
Highlights
Solar energetic particle (SEP) events have been shown to affect the Earth’s atmosphere due to the depletion of stratospheric ozone[1,2] and to be potentially hazardous for life on Earth due to the following increase of solar ultra-violet (UV) irradiance at the surface[3]
The model results are representative for a hemispheric estimate, which after local rescaling is sufficient for the analysis of relative annual variability, as used in our study
Based on our 3-D modelling results and observational data analysis, we conclude that the solar energetic particle (SEP) event of 774–775 AD was able to decrease the stratospheric ozone for more than one year and to modulate the surface weather
Summary
Solar energetic particle (SEP) events have been shown to affect the Earth’s atmosphere due to the depletion of stratospheric ozone[1,2] and to be potentially hazardous for life on Earth due to the following increase of solar ultra-violet (UV) irradiance at the surface[3]. The event was short in duration (possibly including several pulses) with a very hard energy spectrum, as estimated using the ratio of different cosmogenic isotopes[9] It was 40–50 times stronger than the largest directly observed event (23-Feb-1956)[6,9], making the event the strongest known during the last 11 millennia[4,12]. It is so distinct in the 10Be data (Fig. 1 and Fig. S1 in Supplementary Materials (SM)) that it serves as a tie point for ice core dating[10]. We model this event and its atmospheric effects and compare it to extensive ice core data
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