Full Dynamical Model (SOCOL:14C-Ex) of 14C Atmospheric Production and Transport in Application to Miyake Events

Abstract

Extreme solar particle events (ESPEs) are caused by rare, enormously strong solar eruptions and can produce globally detectable spikes in tree-ring radiocarbon 14C, known as Miyake events, which serve as precise chronological tie-points and indicators of extreme solar activity. After production, radiocarbon is subjected to the complex carbon cycle, including large-scale atmospheric transport, which is crucially important for fast and strong Miyake events with highly inhomogeneous 14C production. A new 3D dynamical model, SOCOL:14C-Ex, of the radiocarbon atmospheric production and transport is presented here, which can model fast changes in the 14C atmospheric concentrations with high temporal and spatial resolution. Precise response curves of $Δ^{14}$C to a reference ESPE (100xGLE#69) were computed for various event dates. They can be directly applied to analyse Miyake events under different conditions. Seven strong events over the past 14 millennia (AD 993, AD 774, 664 BC, 5260 BC, 5411 BC, 7177 BC, and 12351 BC) were analysed by fitting the reference curves to the available annual D14C data, identifying the most probable values and confidence intervals of their parameters -- strength, event's date and background level. By applying corrections for the geomagnetic and atmospheric (CO2) factors, the strengths of the corresponding ESPEs were assessed. The strongest ESPE is confirmed to be that of 12351 BC, while that of AD 774 remains the strongest event during the Holocene. To conclude, a new tool, based on the radiocarbon atmospheric transport model SOCOL:14C-Ex, is presented to analyse fast changes in the $^{14}$C production.

Figures (10)

• Figure 1: Integral omnidirectional fluence of solar energetic particles, $F(>$$E$) for the GLE #69 (20-Jan-2005) as reconstructed from ground-based and space-borne data (blue curve -- Koldobskiy2021). The red dashed curve is scaled up by a factor $K$=100, representing the reference ESPE spectrum used here.
• Figure 2: Examples of the time response functions of $\Delta^{14}$C to the reference ESPE (Figure \ref{['fig:spectrum']}) for two geographical locations: Central Europe (44.31$^\circ$ N, 5.52$^\circ$ E -- panel a), and Patagonia (41.9$^\circ$ S, 72.67$^\circ$ W -- panel b). Different curves correspond to different dates of the ESPE occurrence, as indicated in the legend: 20-Jan, 01-Apr, 20-Jul, and 20-Oct of year zero (1865 in the simulation), denoted as $t1$ -- $t4$, respectively. Shaded areas approximately indicate the tree growth periods. The results are shown with daily resolution, depicting, in particular, meteorological noise on the synoptic scale.
• Figure 3: Geographical distribution of modelled near-ground overland $\Delta^{14}$C values caused by the reference ESPE, which took place on 20-Jan-1865. The distribution is shown for the day of 20-Jul-1867. The LHS panel depicts the latitudinal zonal (over land) mean.
• Figure 4: An example of interpolating the response curves for the first year of the ESPE. Panel a: full-model calculated responses for 20-Jan (red) and 01-Apr (blue) in the Northern hemisphere -- similar to Figure \ref{['fig:daily']}, along with interpolated curves (grey) shown for every tenth day. Panel b: Similar to panel a, but all the curves start on the event's date.
• Figure 5: Estimated effect of including a Glacial-type biosphere in the model. The plot shows the percentile difference between the near-ground air $^{14}$C concentrations in Southern Europe, averaged over April--September for years following a reference ESPE occurring at the zero date. The concentrations were computed by the SOCOL:14C-Ex model runs for the Glacial and Holocene vegetation types. The difference is shown as Glacial minus Holocene conditions. The error bars represent the statistical uncertainties between model runs.