Title:	Past Solar Storms: The links between solar storms and solar activity
DNr:	NAISS 2024/5-423
Project Type:	NAISS Medium Compute
Principal Investigator:	Raimund Muscheler <raimund.muscheler@geol.lu.se>
Affiliation:	Lunds universitet
Duration:	2024-08-30 – 2025-03-01
Classification:	10503
Keywords:

Abstract

Our Sun is a remarkably stable energy source, crucial for life on Earth. However, the Sun exhibits variations over a wide range of timescales. Occasionally, violent eruptions on the Sun’s surface, known as solar storms, release energetic particles that can damage our modern society. For example, one of the largest known solar storms, the “Carrington Event,” occurred in 1859, significantly affecting the telegraph system, one of the few systems dependent on electricity at that time. Today, the Sun is constantly monitored, and a wealth of information about its variability has been obtained from ground-based and satellite observations. However, historical observations and indirect proxy data demonstrate that the Sun can produce solar storms orders of magnitude larger than those observed during the space era. Presently, we do not know the recurrence rate of large solar storms or how these events are linked to solar activity. Mapping these linkages may help us understand the underlying processes and predict the risks of future events. To fill this important knowledge gap, cosmogenic radionuclides (e.g., Be-10 and Cl-36) measured from ice cores could serve as “natural detectors” of past solar activity. However, significant uncertainty remains in using Be-10 and Cl-36 as reliable solar proxies. These radionuclides are produced in the atmosphere, but measurements are taken from ground archives (e.g., ice cores). Therefore, it is crucial to evaluate how transport and deposition processes influence the solar signal in the radionuclides measured from ice cores. Supported by my ERC Advanced Grant (2025-2029), titled "Past Solar Storms: The Links Between Solar Storms and Solar Activity," I will employ two state-of-the-art global climate models to simulate the transport and deposition processes of cosmogenic radionuclides: ECHAM6.3-HAM2.3 (https://redmine.hammoz.ethz.ch/projects/hammoz) and GEOS-Chem (https://geoschem.github.io/). Control simulations over the present period and a series of sensitivity simulations will be performed. The first control simulation will focus on the recent 70 years to model the atmospheric transport and deposition of Be-10 and Cl-36 with two climate models, one of which will be driven by re-analysis data in an effort to better understand the link between climate, meteorological and solar signals in ice core radionuclide data and to identify know solar storm events in radionuclide data that presently cannot be robustly inferred. The second aspect will focus on sensitivity tests and paleo-events where the theoretical expectations for solar storm signals will be re-assessed (hemispheric biases, Be-10 and Cl-36 differences, local differences, accumulation rate dependencies). These simulations aim to significantly advance our knowledge of the transport and deposition processes of cosmogenic radionuclides, therefore reducing uncertainties in their application as natural detectors of past solar activity.