High-Resolution Spectral and Anisotropy Characteristics of Solar Protons During the GLE N(circle)73 on 28 October 2021 Derived with Neutron-Monitor Data Analysis

The first ground-level enhancement of the current Solar Cycle 25 occurred on 28 October 2021. It was observed by several space-borne and ground-based instruments, specifically neutron monitors. A moderate count-rate increase over the background was observed by high-altitude polar stations on the South Pole and Dome C stations at the Antarctic plateau. Most of the neutron monitors registered only marginal count-rate increases. Using detrended records and employing a method verified by direct space-borne measurements, we derive the rigidity spectra and angular distributions of the incoming solar protons in the vicinity of Earth. For the analysis, we employed a newly computed and parameterized neutron-monitor yield function. The rigidity spectra and anisotropy of solar protons were obtained in their time evolution throughout the event. A comparison with the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron (SOHO/ENRE) experiment data is also performed. We briefly discuss the results derived from our analysis

A new model of cosmogenic production of radiocarbon 14C in the atmosphere

We present the results of full new calculation of radiocarbon 14C production in the Earth atmosphere, using a numerical Monte-Carlo model. We provide, for the first time, a tabulated 14C yield function for the energy of primary cosmic ray particles ranging from 0.1 to 1000 GeV/nucleon. We have calculated the global production rate of 14C, which is 1.64 and 1.88 atoms/cm2/s for the modern time and for the pre-industrial epoch, respectively. This is close to the values obtained from the carbon cycle reservoir inventory. We argue that earlier models overestimated the global 14C production rate because of outdated spectra of cosmic ray heavier nuclei. The mean contribution of solar energetic particles to the global 14C is calculated as about 0.25% for the modern epoch. Our model provides a new tool to calculate the 14C production in the Earth's atmosphere, which can be applied, e.g., to reconstructions of solar activity in the past.Comment: Published in EPSL, 337, 114, 201

Ionization effect in the Earth’s atmosphere due to cosmic rays during the GLE # 71 on 17 May 2012

Abstract Nowadays the systematic study of the possible effect of precipitating high-energy particles on atmospheric physics and chemistry is in great expansion. Most of the recent models studying the precipitating energetic particles effects in the Earth’s atmosphere are based on reliable quantification of the induced ionization, that is, the cosmic ray impact ionization, which is extensively studied over the last decade. While the galactic cosmic rays are the main source of ionization in the Earth’s stratosphere and troposphere, the energetic particles of solar origin can significantly enhance the ion production following strong solar eruptions, specifically over the polar caps. A particular interest represents solar protons observed by ground-based detectors, viz. the so-called ground level enhancements (GLE), observed as an increase of the count rate of e.g. neutron monitors. Here, employing 3-D Monte Carlo model, we computed the solar protons induced atmospheric ionization during the moderate GLE # 71 on 17 May 2012. The ion production rates were computed during various stages of the event as a function of the altitude above sea level using derived by verified model particles spectra. The 24 h averaged ionization effect relative to the average due to the galactic cosmic rays was computed at several depths in the atmosphere

Preface to measurement, specification and forecasting of the Solar Energetic Particle (SEP) environment and Ground Level Enhancements (GLEs)

Abstract The Sun emits energetic particles following eruptive events such as solar flares and Coronal Mass Ejections (CMEs). Solar Energetic Particles (SEPs) arrive in bursts known as Solar Particle Events (SPEs), which penetrate into the Earth’s magnetosphere. SEPs with large enough energy induce a complicated atmospheric cascade, which secondary particles lead to an enhancement of count rate of ground-based detectors e.g. Neutron Monitors (NMs). This class of SEPs is therefore referred as Ground Level Enhancements (GLEs). The characterisation of the high-energy SEPs environment with corresponding space weather effects is important for space flights, aviation, and satellite industry. In this topical issue recent developments, addressing important user needs in the space radiation environment domain are published. Some articles are relevant to the specification of the SEP environment whilst others focus on space weather prediction of SEP fluxes. Catalogues based on measurement and processing of SEPs including ground-based data, and modelling of aircrew radiation exposure during major events are also presented

Current status and possible extension of the global neutron monitor network

Abstract The global neutron monitor network has been successfully used over several decades to study cosmic ray variations and fluxes of energetic solar particles. Nowadays, it is used also for space weather purposes, e.g. alerts and assessment of the exposure to radiation. Here, we present the current status of the global neutron monitor network. We discuss the ability of the global neutron monitor network to study solar energetic particles, specifically during large ground level enhancements. We demonstrate as an example, the derived solar proton characteristics during ground level enhancements GLE #5 and the resulting effective dose over the globe at a typical commercial jet flight altitude of 40 kft (≈12,200 m) above sea level. We present a plan for improvement of space weather services and applications of the global neutron monitor network, specifically for studies related to solar energetic particles, namely an extension of the existing network with several new monitors. We discuss the ability of the optimized global neutron monitor network to study various populations of solar energetic particles and to provide reliable space weather services

The altitude profile of the cosmic ray atmospheric cutoff

Abstract Neutron monitors are the main ground-based instruments for continuous measurements the cosmic-ray intensity operating over more than five decades. Those instruments are energy-integrating detectors with count rates governed by the atmospheric and geomagnetic cutoffs. The geomagnetic cutoff dominates (up to 17 GV in rigidity) over most of the globe. However, it is negligible in the polar regions, and there, the atmospheric cutoff is important. The atmospheric cutoff depends on the elevation of the instrument above sea level (on the atmospheric depth), and it is estimated as ~1 GV for cosmic-ray protons at sea level. However, the cutoff is not precisely known at higher altitudes. This is specifically important for studies based on high-altitude polar neutron monitors, which count rate is solely defined by the atmospheric cutoff. We present a newly estimated altitude profile of the atmospheric cutoff for cosmic-ray protons, which can be used in analysis of both galactic cosmic rays and solar energetic particles. We computed the profile using two methods. The first one is based on Monte Carlo simulation of the cosmic-ray induced cascade in the atmosphere with the PLANETOCOSMICS code. The second one uses recently computed and verified neutron monitor yield function by Mishev et al., 2020, which considers the efficiency of the instrument. Both methods agree reasonably well, though the yield-function based one provides a more conservative result, as expected. There are two definitions of solar-particle sub-GLE (sub-Ground-Level-Enhancement) events by Raukunen et al. (2018) and Poluianov et al. (2018) based on different principles. Considering the derived in this study atmospheric cutoff at altitudes about 3000 m a.s.l., we conclude: there is no contradiction between the definitions

About the altitude profile of the atmospheric cut-off of cosmic rays:new revised assessment

Abstract Cosmic rays, high-energy subatomic particles of extraterrestrial origin, are systematically measured by space-borne and ground-based instruments. A specific interest is paid to high-energy ions accelerated during solar eruptions, so-called solar energetic particles. In order to build a comprehensive picture of their nature, it is important to fill the gap and inter-calibrate ground-based and space-borne instruments. Here, we focus on ground-based detectors, specifically neutron monitors, which form a global network and provide continuous recording of cosmic ray intensity and its variability, used also to register relativistic solar energetic particles. The count rate of each neutron monitor is determined by the geomagnetic and atmospheric cut-offs, both being functions of the location. Here, on the basis of Monte Carlo simulations with the PLANETOCOSMICS code and by the employment of a new verified neutron monitor yield function, we assessed the atmospheric cut-off as a function of the altitude, as well as for specific stations located in the polar region. The assessed in this study altitude profile of the atmospheric cut-off for primary cosmic rays builds the basis for the joint analysis of strong solar proton events with different instruments and allows one to clarify recent definitions and related discussions about the new sub-class of events, so-called sub-ground-level enhancements (sub-GLEs)

Performance of the current and extended global NM network for solar particle registration and analysis

Abstract Over several decades, the global neutron monitor network was extensively and with undoubtful success used to study cosmic ray variations and fluxes of accelerated solar ions, the latter known as solar energetic particles. Recently, it has been used also for space weather purposes, specifically for alerts, and to provide crucial information necessary for assessment of different space weather effects, specifically the assessment of the exposure to radiation at flight altitudes. Here, we discuss the current status and applications of the global neutron monitor network, precisely its capability to study solar energetic particles, namely assessment of their spectral and angular distribution, during strong solar proton events e.g. those leading to ground level enhancements. Several examples are presented, accordingly. We also discuss the existing gaps in the network and propose an improvement of the network, namely a plan for an extension of the existing network with several new stations, in order to provide a more accurate analysis of strong solar proton events and to respond to the current space weather demands and services. We discuss the ability of the optimized global neutron monitor network to study various populations of solar energetic particles and to provide reliable space weather services

Fluences of solar energetic particles for last three GLE events:comparison of different reconstruction methods

Abstract Fluxes of solar energetic particles (SEPs), produced and accelerated in and in the vicinity of the Sun, are an important part of cosmic ray induced terrestrial effects such as ionizing radiation on the Earth’s orbit, which affects the exposure to radiation in space as well as the atmospheric ionization. Calculation of these effects requires the knowledge of the integral fluences of SEPs. High-energy solar particles are subject of special interest since they can significantly contribute to the total radiation dose and/or ionization. The main instrument to study the high-energy SEP events is a network of ground-based neutron monitors (NMs), used over the years to register a specific class of SEP, which is called ground-level enhancement (GLE) events. Up today, we possess records from 72 GLE events. Reconstruction of SEP integral and differential fluxes for GLE events using NM data is not an easy task, requires a careful and precise calculation of particle transport in the magnetosphere, atmosphere, and detector itself. In this work, we compare two methods of fluence reconstruction, “fast” and “full”, for the last three registered GLE events and additionally verify one of them using PAMELA experimental data