New consistent and precise computations of the production of five cosmogenic radioisotopes, ⁷Be, ¹⁰Be, ¹⁴C, ²²Na, and ³⁶Cl, in the Earth's atmosphere by cosmic rays are presented in the form of tabulated yield functions. For the first time, a detailed set of the altitude profiles of the production functions is provided which makes it possible to apply the results directly as input for atmospheric transport models. Good agreement with most of the earlier published works for columnar and global isotopic production rates is shown. Altitude profiles of the production are important, in particular for such tasks as studies of strong solar particle events in the past, precise reconstructions of solar activity on long‐term scale, tracing air mass dynamics using cosmogenic radioisotopes, etc. As an example, computations of the ¹⁰Be deposition flux in the polar region are shown for the last decades and also for a period around 780 A.D. and confronted with the actual measurements in Greenland and Antarctic ice cores.

Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ fluxes are presented. The measurements are based on 100 million ${}^4\mathrm{He}$ nuclei in the rigidity range from 2.1 to 21 GV and 18 million ${}^3\mathrm{He}$ from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the ${}^3\mathrm{He}/{}^4\mathrm{He}$ flux ratio is measured for the first time. Below 4 GV, the ${}^3\mathrm{He}/{}^4\mathrm{He}$ flux ratio was found to have a significant long-term time dependence. Above 4 GV, the ${}^3\mathrm{He}/{}^4\mathrm{He}$ flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law $\propto R^{\mathrm{\Delta }}$ with $\mathrm{\Delta }=-0.294\pm 0.004$. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies.

The Sun is magnetically active and often produces eruptive events on different energetic and temporal scales. Until recently, the upper limit of such events was unknown and believed to be roughly represented by direct instrumental observations. However, two types of extreme events were discovered recently: extreme solar energetic particle events on the multi-millennial time scale and super-flares on sun-like stars. Both discoveries imply that the Sun might rarely produce events, called extreme solar events (ESE), whose energy could be orders of magnitude greater than anything we have observed during recent decades. During the years following these discoveries, great progress has been achieved in collecting observational evidence, uncovering new events, making statistical analyses, and developing theoretical modelling. The ESE paradigm lives and is being developed. On the other hand, many outstanding questions still remain open and new ones emerge. Here we present an overview of the current state of the art and the forming paradigm of ESE from different points of view: solar physics, stellar–solar projections, cosmogenic-isotope data, modelling, historical data, as well as terrestrial, technological and societal effects of ESEs. Special focus is paid to open questions and further developments. This review is based on the joint work of the International Space Science Institute (ISSI) team #510 (2020–2022).

New recently installed high-altitude polar neutron monitors (NMs) have made the worldwide NM network more sensitive to strong solar energetic particle (SEP) events, registered at ground level, namely ground-level enhancement (GLE) events. The DOMC/B and South Pole NMs in addition to marginal cut-off rigidity also possess lower atmospheric cut-off compared to the sea level. As a result, the two high-altitude polar NM stations are able to detect lower energy SEP events, which most likely would not be registered by the other (near sea level) NMs. Here, we consider several candidates for such type of events called sub-GLEs. Using the worldwide NM database (NMDB) records and an optimization procedure combined with simulation of the global NM network response, we assess the spectral and angular characteristics of sub-GLE particles. With the estimated spectral characteristics as an input, we evaluate the effective dose rate in polar and sub-polar regions at typical commercial flight altitude. Hence, we demonstrate that the global NM network is a useful tool to estimate important space weather effects, e.g., the aircrew exposure due to cosmic rays of galactic and/or solar origins.