O. N. Kryakunova

Large episodes of solar activity of the 25th cycle, an extreme Forbush decrease event on 19 January 2026, a series of Forbush effects in November 2025, and an event of ground-level enhancement (GLE 77) on 11 November 2025 have left prominent traces in the monitoring data obtained at a height of 3340 m a.s.l. from the detector facilities of the Tien Shan High-Mountain Cosmic Ray Station. The effects these events have caused on the flux of galactic cosmic rays in the several-GeV energy range, as registered with the standard NM64-type neutron supermonitor, are compared here with their influence on the local neutron and gamma radiation background in the high-mountain environment, which was observed in the counting rate records of the thermal neutron and MeV-order-energy gamma radiation detectors also installed at the station.

During the NMDB Meeting 2025, which took place in March 2025 in Athens, Greece, more than 40 contributions (oral and e-posters) were presented. Particular emphasis was given to the intense events of solar, interplanetary and geomagnetic nature that occurred in 2024. The topics of the NMDB upgrade and expansion (with new neutron measurements and other scientific programs) as well as the importance of cosmic ray intensity measurements over time and the development of new applications were addressed. In the following overview, a brief description of the meeting’s contributions is provided.

An intensive disturbance of the heliosphere originating from a series of solar flares at the end of May 2025 revealed itself as an extremely strong Forbush decrease in the flux of galactic cosmic rays, which was observed at the worldwide network of neutron monitoring starting from 1 June 2025. Together with an effect on the intensity of cosmic rays measured at a height of 3340 m a.s.l. by a standard NM64 neutron supermonitor of the Tien Shan High-Mountain Cosmic Ray Station, the impact of this event was detected here as a synchronous depression in the counting rates of thermal neutrons and hard gamma rays, the background intensity of which is also continuously tracked in the environment of the station. This observation may be profitable for development of an alternative technique applicable for studying large disturbances in the heliosphere, besides using the traditional method of neutron monitor. An analysis of the frequency of the events of multiple-neutron generation in the Tien Shan supermonitor demonstrated that the influence of the heliosphere disturbance on the hadronic component of cosmic rays did most distinctively reveal itself in the energy range of (3–20) GeV.

В работе представлен анализ события, зарегистрированного 1-10 июня 2025 г. нейтронным монитором AATB (Алматы, Казахстан, 3340 м над уровнем моря, жесткость геомагнитного обрезания R = 5.9 ГВ). Амплитуда понижения интенсивности космических лучей, зарегистрированной нейтронным монитором, составила около 12 %, что позволяет отнести событие к числу больших Форбуш-эффектов. Источником возмущений явилась активная область AR 14100, в которой произошла серия вспышек классов M3.4 и M8.1 (30–31 мая 2025 г.), сопровождавшихся быстрыми гало-CME корональными выбросами масс (КВМ) типа гало со скоростями до 1700 км/с. Сопоставление данных нейтронного монитора с межпланетными параметрами показало классическую структуру межпланетного КВМ, включающую межпланетную ударную волну 1 июня, 05:45 UT, область возмущенной сжатой плазмы и область коронального выброса до 2 июня, 01:10 UT. Событие сопровождалось развитием сильной геомагнитной бурей, пик которой пришёлся на 2 июня. Результаты демонстрируют тесную взаимосвязь между солнечной активностью, динамикой межпланетного КВМ и модуляцией потоков галактических космических лучей ГКЛ, подчёркивая значимость комплексного подхода к диагностике и прогнозированию космической погоды.

Solar eruptive events such as flares and coronal mass ejections can accelerate charged particles up to nearly relativistic energies producing so-called solar energetic particles (SEPs). Some of those SEPs can propagate towards Earth and be registered by, e.g., particle detectors onboard satellites. Favourable acceleration conditions make strong SEP events possible with a high flux of high-energy (> 500 MeV) protons, which can be registered even on the ground by neutron monitors (NMs) as rapid enhancements of their count rate over the background. Such events are accordingly called ground-level enhancements (GLEs). GLEs are rare, with only 73 events registered from 1942 to 2023, and three more GLEs 74 – 76 occurred in 2024, close to the maximum of solar activity. In this work, we report GLE 75 that happened on 8 June 2024, initially missed during real-time monitoring, but identified retrospectively. The SEP event, which induced the GLE, was associated with a flare from the solar active region 13697 (13664 on the previous solar rotation). It caused statistically significant increases in the count rate of NMs Dome C, South Pole, and Peawanuck, as well as in the proton intensity measured by Geostationary Operational Environmental Satellite GOES-16. Here, we show the GLE in NM data, describe the procedure of evaluation of its statistical significance, and present the analysis with reconstruction of the spectral and angular SEP distributions.

Based on measurements of magnetospheric electron fluxes with energies >2 MeV in geostationary orbits, solar wind (SW) velocity, and geomagnetic activity for the period 1995–2023, a catalogue of electron flux enhancements (with fluence exceeding 108 particles cm−2 st−1 d−1) has been compiled. For the events of this catalogue, interplanetary disturbances have been determined, after which high-energy electron fluxes (HEEF) begin to increase, and their solar sources have been established. It is found that in 97.2 per cent of cases, one of the solar sources of interplanetary disturbances that led to electron flux increases were high-speed streams from coronal holes (HSSs from CHs), in particular only HSSs from CHs were observed in 52.5 per cent of events, and in the remaining cases, HSSs from CHs were observed together with coronal mass ejections (CMEs) after solar flares and/or filaments disappearance. The average behaviour of the HEEF, SW velocity, and geomagnetic activity indices for events associated with the arrival of an HSS from CH to the Earth is obtained. It is shown that electron flux enhancements events associated with interplanetary disturbances from HSSs from CHs and from CMEs differ in duration and maximum electron fluence.

The Forbush effects (FEs) in cosmic rays associated with interplanetary disturbances caused by the disappearance of solar filaments (DSFs) outside active regions (ARs) are considered. In total, 481 FEs were detected for 1995–2023 using the database of Forbush Effects and Interplanetary Disturbances (FEID). The behavior of the cosmic ray density was calculated using the Global Survey Method (GSM). The distributions of the FE numbers depending on their duration and magnitude, as well as on the characteristics of the interplanetary and near-Earth medium, were obtained. It is found that the average duration of such FEs (33.4 ± 0.5 h) is almost the same as for events associated with CMEs from ARs, but the average magnitude is much smaller (0.83 ± 0.03%). It is also shown that coronal mass ejections (CMEs) caused by DSFs are often low-speed interplanetary disturbances (with an average maximum SW speed of 423.2 ± 3.5 km/s), the velocities of which are close to the speed of the background solar wind (SW). During FEs associated with CMEs after DSFs outside ARs, on average, unsettled geomagnetic activity is observed. Magnetic storms were recorded only in 19% of events. Lower values of FE magnitude and geomagnetic activity are associated with weakened magnetic fields and low speeds of such interplanetary disturbances.

A brief overview is given regarding the presentations delivered at the NMDB@Athens meeting which was held, in a hybrid fashion, in September 2022. Participants joined both remotely but also physically at the National and Kapodistrian University of Athens, Greece. Unlike traditional cosmic ray meetings and conferences where the focus is mainly on the science related to neutron monitor measurements, the ›NMDB@Athens‹ meeting uniquely also addresses hardware issues related to these instruments and, importantly, also databases where different data products can be accessed by a growing and increasingly diverse user base. The present overview outlines and introduces the more detailed articles contained in the proceedings.

Changes in the intensity of galactic cosmic rays on Earth and beyond the boundary of the magnetosphere occur earlier than an increase in the flux of high-energy magnetospheric electrons with energy >2 MeV in the geostationary orbit, so the behavior of galactic cosmic rays before and during electron flux enhancements can provide valuable information about the processes occurring in near-Earth space at this time. The density and vector anisotropy of galactic cosmic rays for 453 events of high-energy magnetospheric electron flux enhancements over the period 1996-2020 were calculated by the Global Survey Method (GSM). Some examples of these events, which are characteristic of different classes of solar sources, are considered. The behavior of the density and vector anisotropy of galactic cosmic rays before and during electron flux enhancements in events connected with the arrival at Earth of high-speed streams from coronal holes, coronal mass ejections associated with solar flares or disappearing solar filaments is revealed.

Coefficients of correlation are calculated for the daily electron fluence, solar wind velocity, and the Ар-index of geomagnetic activity with d