Extreme solar particle events (ESPEs) are rare and the most potent known processes of solar eruptive activity. During ESPEs, a vast amount of cosmogenic isotopes (CIs) 10Be, 36Cl and 14C can be produced in the Earth’s atmosphere. Accordingly, CI measurements in natural archives allow us to evaluate particle fluxes during ESPEs. In this work, we present a new method of ESPE fluence (integral flux) reconstruction based on state-of-the-art modeling advances, allowing to fit together different CI data within one model. We represent the ESPE fluence as an ensemble of scaled fluence reconstructions for ground-level enhancement (GLE) events registered by the neutron monitor network since 1956 coupled with satellite and ionospheric measurements data. Reconstructed ESPE fluences appear softer in its spectral shape than earlier estimates, leading to significantly higher estimates of the low-energy (E<100 MeV) fluence. This makes ESPEs even more dangerous for modern technological systems than previously believed. Reconstructed ESPE fluences are fitted with a modified Band function, which eases the use of obtained results in different applications.

41 thousand years ago, the Laschamps geomagnetic excursion caused Earth’s geomagnetic field to drastically diminish to ~4% of modern values and modified the geomagnetic dipole axis. While the impact of this geomagnetic event on environmental factors and human lifestyle has been contemplated to be linked with modifications in the geospace environment, no concerted investigation has been conducted to study this until recently. We present an initial investigation of the global space environment and related plasma environments during the several phases of the Lachamps event using an advanced multi-model approach. We use recent paleomagnetic field models of this event to study the paleomagnetosphere with help of the global magnetohydrodynamic model BATS-R-US. Here we go beyond a simple dipole approximation but consider a realistic geomagnetic field configuration. The field is used within BATS-R-US to generate the magnetosphere during discrete epochs spanning the peak of the event. Since solar conditions have remained fairly constant over the last ~100k years, modern estimates of the solar wind were used to drive the model. Finally, plasma pressure and currents generated by BATS-R-US at their inner boundary are used to compute auroral fluxes using a stand-alone version of the MAGNIT model, an adiabatic kinetic model of the aurora. Our results show that changes in the geomagnetic field, both in strength and the dipole tilt angle, have profound effects on the space environment and the ensuing auroral pattern. Magnetopause distances during the deepest phase of the excursion match previous predictions by studies like Cooper et al. (2021), while high-resolution mapping of magnetic fields allow close examination of magnetospheric structure for non-dipolar configurations. Temporal progression of the event also exhibits rapid locomotion of the auroral region over ~250 years along with the movement of the geomagnetic poles. Our estimates suggest that the aurora extended further down, with the center of the oval located at near-equatorial latitudes during the peak of the event. While the study does not find evidence of any link between geomagnetic variability and habitability conditions, geographic locations of the auroral oval coincide with early human activity in the Iberian peninsula and South China Sea.

A new model of cosmogenic tritium (H) production in the atmosphere is presented. The model belongs to the CRAC (Cosmic-Ray Atmospheric Cascade) family and is named as CRAC:3H. It is based on a full Monte-Carlo simulation of the cosmic-ray induced atmospheric cascade using the Geant4 toolkit. The CRAC:3H model is able, for the first time, to compute tritium production at any location and time, for any given energy spectrum of the primary incident cosmic ray particles, explicitly treating, also for the first time, particles heavier than protons. This model provides a useful tool for the use of H as a tracer of atmospheric and hydrological circulation. A numerical recipe for practical use of the model is appended.

The worldwide network of neutron monitors (NMs) is the primary instrument to study cosmic-ray variability on time scales of up to 70 years. Since the 1950s, 147 NMs with publicly available data have been in operation, and their records are archived in and distributed through different repositories and data sources. A comprehensive analysis of all available NM datasets (300 datasets from 147 NMs) is performed here to check the quality and consistency of the data. The data sources include World Data Center for Cosmic Rays (WDCCR), the Neutron Monitor Database (NMDB), the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation (IZMIRAN) and individual station/institution databases. It was found that The data from the same NM can be non-identical and of different quality in different sources. We give and tabulate here a recommendation for the optimal data source of each NM. We also present here a list of 29 ‘prime’ stations with the longest and most reliable data. Verified datasets for these prime stations are provided as supplementary information.

We compare results of the solar high-energy proton detection with the neutron monitor network in Ground Level Enhancement (GLE) events and the data of pion-decay gamma-ray emission produced by high-energy protons interacting at the Sun. Observational data support the idea of a common origin of the GLE-producing protons and the protons interacting at the Sun to produce sustained gamma-ray emission. Then we discuss capabilities of the CME bow-shock acceleration models to explain the observational data and argue for the flare and CME synergy in production of high-energy protons in the long duration events.

We present a new open-source tool for magnetospheric computations, that is modelling of cosmic ray propagation in the geomagnetosphere, named the “Oulu - Open-source geomagneToSphere prOpagation tool” (OTSO). A tool of this nature is required in order to interpret experiments and study phenomena within the cosmic ray research field. Within this work OTSO is applied to the investigation several ground level enhancement events. Here, we demonstrated several applications of OTSO, namely computation of asymptotic directions of selected cosmic ray stations, effective rigidity cut-off across the globe at various conditions within the design, general properties, including the magnetospheric models employed. A comparison and validation of OTSO with older widely used tools such as MAGNETOCOSMICS was performed and good agreement was achieved. An application of OTSO for providing the necessary background for analysis of two notable ground level enhancements is demonstrated and the their spectral and angular characteristics are presented.