Welcoming for NMDB@Athens conference

Prof. H. Mavromichalaki on behalf of the organizing committee welcomes everyone to the 'NMDB@Athens' conference. The obituaries for Dr. Evgenia Eroshenko and Prof. Lev Dorman who recently passed away are following

Cosmic radiation exposure of aviators for solar cycles 23 and 24

Assessing the radiation exposure of aviators and frequent flyers requires the study of the cosmic ray showers inside the Earth’s atmosphere. DYASTIMA / DYASTIMA-R is a Geant4 based software application, implemented by the Athens Cosmic Ray Group which allows the study of the evolving secondary particles cascades inside the atmosphere, as well as radiation dosimetry calculations (ambient dose equivalent rate) at different atmosphe - ric altitudes, geographic coordinates and magnetic cut-off rigidity. Results for various scenarios, as calculated by DYASTIMA/DYASTIMA-R, are provided as a federated product through the European Space Agency Space Situational Awareness of the Space Radiation Service Centre Network, while the DYASTIMA software is provi- ded through the Athens Neutron Monitor Station (A.Ne.Mo.S.) portal. Initial results for the assessment of the radiation exposure during the last Solar Cycles 23 and 24 are presented in this work, covering the most usual flying altitudes. The results indicate the dependence of the dose rate on the magnetic cut-off rigidity threshold, with higher dose rates at high geographic latitudes, as well as the anti-correlation of cosmic ray intensity with the solar activity, as higher dose rates are observed during solar minimum conditions

Precursory signals of Forbush decreases with and without shock wave

Many previous studies have shown that before the beginning of a Forbush Decrease (FD) of the cosmic ray intensity, a precursor signal can be observed. All these surveys were focused on FDs that are associated with a sudden storm com- mencement (SSC). In this work we demonstrate that precursors could also be observed in events without a SSC that is determined by an abrupt increase of the interplanetary magnetic field. The type of precursory signals and their diversity among the events are the main purpose of this study. We try to figure out similarities and differences on the signals and the associated events from both categories in the last fifty years, from 1969 to 2019, using the same selection criteria of the under investigation FDs. Simultaneously the orientation of the upcoming solar disturbances in comparison to the way they configure the increase of the interplanetary magnetic field and create these signals are discussed

Magnetospheric effects on cosmic rays during the magnetic storm of March 2015

Cosmic ray variations of magnetospheric origin during the magnetic storm on 17th of March 2015 were studied. Cosmic ray intensity data were obtained from the neutron monitor database (NMDB) and the data of the Dst index were taken from World Data Center for Geomagnetism, Kyoto. The global survey method was employed for the calculation of changes in the cutoff rigidities throughout the storm. A correlation analysis between the Dst index and the calculated cutoff rigidity variations was performed for each cosmic ray station. The most essential decrease in cutoff rigidities occured when the Dst index was around the value of -234nT. A latitudinal distribution of the cutoff rigidities was acquired, showing that the maximum effect took place at mid-latitude stations with rigidities around 8-10GV. During the examined event the maximum change in cutoff rigidity was observed at Athens station where the decrease of the cutoff rigidity reached the value of 1.07GV. Furthermore, corrections of cosmic ray intensity due to the magnetospheric effect were calculated using the derived cutoff rigidities showing a discperancy with the observed values at mid- and low- latitude stations

Relationship of the characteristics of large Forbush decreases and the heliolongitude of their sources

In this investigation the different features and characteristics of Forbush decreases, with emphasis on large For- bush decreases (≥4%) and their association to solar sources, are being examined. According to the heliolongitude of the solar source, the events under study were separated into three subcategories: western (21º ≤ heliolongitude ≤ 60º), eastern (-60º ≤ heliolongitude ≤ -21º) and central (-20º ≤ heliolongitude ≤ 20º). The selected events cover the time period 1967 - 2017. The ‘Global Survey Method’ was used for analyzing the Forbush decreases, along with data on solar flares, solar wind speed, geomagnetic indices (Kp and Dst), and interplanetary magnetic field. In ad - dition, the superimposed epoch method was applied in order to plot the time profiles for the aforementioned group of events. This detailed analysis reveals interesting results concerning the features of cosmic ray decreases in re- gard to the heliolongitude of the solar sources. Moreover, it is also shown that large Forbush decreases, regardless of the heliolongitude of the solar source, are accompanied by increased geomagnetic activity and increased aniso- tropy, including anisotropy before the events, which can serve as a typical precursor of Forbush decreases

Atmospheric cosmic ray induced ionization and radiation affecting aviation

Cosmic radiation is a major factor of ionization of the Earth’s atmosphere. Both solar and galactic cosmic rays, which depend on solar activity and geomagnetic field, affect the radiation exposure in the atmosphere. Several models have been created for the estimation of the ionization and radiation dosimetry. In this work, as regards the ionization rate computations the CRAC:CRII model by the University of Oulu (https://cosmicrays.oulu.fi/CRII/CRII.html) was used, while for the estimation of the ambient equivalent dose rate (dH*(10)/dt) we used the validated software DYASTIMA / DYASTIMA-R by the University of Athens (http://cosray.phys.uoa.gr/index.php/applications/dyastima). Both tools are of great importance as they allow us to calculate the respective quantities all over the globe, at the entire atmosphere and for different time periods and solar cycle phases. The study concerns the last two solar cycles 23 and 24 (1996–2019) and specific flight levels of commercial aviation (FL310, FL350 and FL390). The dependance of CRII and dH*(10)/dt on geomagnetic cut-off rigidity, solar activity, cosmic ray intensity, as well as the altitude inside the atmosphere, affect the radiation exposure of the air crew members and frequent flyers, which make the results very interesting for the aviation industr

The updated GLE alert system by ANEMOS

Ground level enhancements (GLEs) of cosmic radiation are the result of solar energetic particles (SEPs) arriving at the Earth, potentially causing major damage to technological systems, but also posing a threat for human health. Intense SEPs, such as the GLE events, can influence the radiation exposure of aircrafts and consequently increase the radiation dose on human crew, but also have an impact on satellites and affect the design of space missions, i.e electronic devices onboard the satellite platforms etc. Therefore, predicting such events is challenging and one of the most important aspects of space weather research. In this work the updated GLE Alert++ System of the Athens Neutron Monitor Station (A.Ne.Mo.S.) implemented by the Athens Cosmic Ray Group of the National and Kapodistrian University of Athens (NKUA) is being presented. Moreover, the innovations of the updated system in relation to the previous version of the GLE Alert Plus are introduced. Finally, the most recent and the first of solar cycle 25 GLE event, GLE73, is discussed. This event was registered by several stations of the worldwide ground-based neutron monitor network. An accurate alert was issued successfully by the ESA R-ESC federated product GLE Alert Plus, as well as by the updated GLE Alert++ System of the NKUA/A.Ne.Mo.S. It should be emphasized that GLE Alert++ signal by NKUA/A.Ne.Mo.S. was issued 45 minutes earlier than the one issued by GOES satellites

THE GROUND-LEVEL ENHANCEMENT OF 2012 MAY 17: DERIVATION OF SOLAR PROTON EVENT PROPERTIES THROUGH THE APPLICATION OF THE NMBANGLE PPOLA MODEL

In this work, we apply an updated version of the Neutron Monitor (NM) Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model, in order to derive the characteristics of the ground-level enhancement (GLE) on 2012 May 17 (GLE71), the spectral properties of the related solar energetic particle (SEP) event, the spatial distributions of the high-energy solar cosmic ray fluxes at the top of the atmosphere, and the time evolution of the locationoftheGLEsource.Ourmodeling,baseduniquelyontheuseofground-levelNMdata,leadstothefollowing mainresults.TheSEPspectrumrelatedtoGLE71wasrathersoftduringthewholedurationoftheevent,manifesting some weak acceleration episodes only during the initial phase (at " 01:55‐02:00UT) and at " 02:30‐02:35UT and " 02:55‐03:00UT. The spectral index of the modeled SEP spectrum supports the coronal mass ejection‐shock driven particle acceleration scenario, in agreement with past results based on the analysis of satellite measurements. During the initial phase of GLE71, the solar proton source at the top of the atmosphere was located above the northernhemisphere,implyingthattheasymptoticdirectionsofviewingofthenorthernhemisphereNMsweremore favorably located for registering the event than the southern ones. The spatial distribution of the solar proton fluxes at the top of the atmosphere during the main phase manifested a large variation along longitude and latitude. At the rigidity of 1GV, the maximum primary solar protonflux resulted on the order of" 3# 10 4 part. m $2 s$ 1 sr $1 GV$ 1

NMDB@Athens: Hybrid symposium on cosmic ray studies with neutron detectors

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

Derivation of relativistic SEP properties through neutron monitor data modeling

The Ground Level Enhancement (GLE) data recorded by the worldwide Neutron Monitor (NM) network are useful resources for space weather modeling during solar extreme events. The derivation of Solar Energetic Particles (SEPs) properties through NM-data modeling is essential for the study of solar-terrestrial physics, providing information that cannot be obtained through the exclusive use of space techniques; an example is the derivation of the higher-energy part of the SEP spectrum. We briefly review how the application of the Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model (Plainaki et al. 2010), can provide the characteristics of the relativistic SEP flux, at a selected altitude in the Earth's atmosphere, during a GLE. Technically, the model treats the NM network as an integrated omnidirectional spectrometer and solves the inverse problem of the SEP-GLE coupling. As test cases, we present the results obtained for two different GLEs, namely GLE 60 and GLE 71, occurring at a temporal distance of ~ 11 years