arXiv subjects

Alexander Mishev

Publications and source records attributed to Alexander Mishev.

9 recordsLinked to original sources

arXiv2026

The First Four Ground-Level Enhancements in the 1940s: Investigation, Digitisation, and Analysis of Forgotten Data

Intense solar eruptions occasionally accelerate solar energetic particles (SEPs) and can trigger ground-level enhancements (GLEs). Among the 77 known GLEs, the first four GLEs, #1 -- 4 in the 1940s took place before the advent of the standard neutron monitors and were missing from the International GLE Database. This data gap challenged their quantification. To overcome this difficulty, we systematically gathered, digitised, and quantified contemporaneous cosmic-ray records pertaining to these GLEs. These data allow us to reconstruct the temporal evolution, with the 1 -- 15 min resolutions, of these GLEs, and broaden their geographical coverage to a global scale. GLEs #1 and #3 exhibited gradual increases in their rise times, measured at 45 +/- 15 and 105 +/- 15 min, respectively. In contrast, GLEs #2 and #4 both exhibited abrupt increases of 15 +/- 15 min. We also compared integral ionisation increase on the standard ionisation chambers and their local geomagnetic cutoff rigidities Pc to qualitatively compare these GLE's spectral hardness: Our result indicates that their spectra are extremely hard for GLEs #2 and #4 and mildly hard for GLEs #1 and #3. GLE #3 showed the greatest integral ionisations for polar detectors among them.

astro-ph.SR↗

arXiv2024

The Solar and Geomagnetic Storms in May 2024: A Flash Data Report

In May 2024, the scientific community observed intense solar eruptions that resulted in a great geomagnetic storm and auroral extension, highlighting the need to document and quantify these events. This study mainly focuses on their quantification. The source active region (AR 13664) evolved from 113 to 2761 millionths of the solar hemisphere between 4 May and 14 May. AR 13664's magnetic free energy surpassed 10^33 erg on 7 May, triggering 12 X-class flares on 8 -- 15 May. Multiple interplanetary coronal mass ejections (ICMEs) were produced from this AR, accelerating solar energetic particles toward Earth. According to satellite and interplanetary scintillation data, at least 4 ICMEs erupted from 13664 eventually overcoming each other and combining. The shock arrival at 17:05 UT on 10 May significantly compressed the magnetosphere down to ~ 5.04 RE, and triggered a deep Forbush Decrease. GOES satellite data and ground-based neutron monitors confirmed a ground-level enhancement from 2 UT to 10 UT on 11 May 2024. The ICMEs induced exceptional geomagnetic storms, peaking at a Dst index of -412 nT at 2 UT on 11 May, marking the sixth-largest storm since 1957. The AE and AL indices showed great auroral extensions that located the AE/AL stations into the polar cap. We gathered auroral records at that time and reconstructed the equatorward boundary of the visual auroral oval to 29.8{\deg} invariant latitude. We compared naked-eye and camera auroral visibility, providing critical caveats on their difference. We also confirmed global enhancements of storm-enhanced density of the ionosphere.

astro-ph.SR↗

arXiv2021

High-altitude polar NM with the new DAQ system as a tool to study details of the cosmic-ray induced nucleonic cascade

A neutron monitor (NM) is, since the 1950s, a standard ground-based detector whose count rate reflects cosmic-ray variability. The worldwide network of NMs forms a rough spectrometer for cosmic rays. Recently, a brand-new data acquisition (DAQ) system has been installed on the DOMC and DOMB NMs, located at the Concordia research station on the Central Antarctic plateau. The new DAQ system digitizes, at a 2-MHz sampling rate, and records all individual pulses corresponding to secondary particles in the detector. An analysis of the pulse characteristics (viz. shape, magnitude, duration, waiting time) has been performed, and several clearly distinguishable branches were identified: (A) corresponding to signal from individual secondary neutrons; (B) representing the detector's noise; (C) double pulses corresponding to the {shortly separated nucleons of the same} atmospheric cascades; (D) very-high multiple pulses which are likely caused by atmospheric muons; and (E) double pulses potentially caused by contamination of the neighbouring detector. An analysis of the waiting time distributions has revealed two clearly distinguishable peaks: peak (I) at about 1 msec being related to the intra-cascade diffusion and thermalisation of secondary atmospheric neutrons; and peak (II) at 30--1000 msec corresponding to individual atmospheric cascades. This opens a new possibility to study spectra of cosmic-ray particles in a single location as well as details of the cosmic-ray induced atmospheric cascades, using the same dataset.

astro-ph.IM↗

arXiv2020

Current status and possible extension of the global neutron monitor network

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 $\#$5 and the resulting effective dose over the globe at a typical commercial jet flight altitude of 40 kft ($\approx$ 12 200m) 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.

physics.space-ph↗

arXiv2016

Computation of ion production rate and short, mid and long term ionization effect by cosmic rays during Bastille day event

The galactic cosmic rays are the main source of ionization in the Earth stratosphere and troposphere. The induced by primary cosmic ray particles ionization is important in various processes related to atmospheric physics and chemistry, specifically the minor constituents. The ion production in the atmosphere is enhanced compared to the average following major solar energetic particles events, specifically over the polar caps. During the solar cycle 23 we observed several strong ground level enhancements, one of the strongest among them been the Bastille day event on 14 July 2000. In the work presented here we apply a full Monte Carlo 3-D model in order to compute the cosmic ray induced ionization. The model is based on atmospheric shower simulation with the PLANETOCOSMICS code and the ion production rate is considered as a superposition of cosmic rays with galactic and solar origin. The ion production rate is computed as a function of the altitude above the sea level and the short, mid and long term ionization effect relative to the average due to galactic cosmic rays is computed.

astro-ph.HE↗

arXiv2016

Analysis of the ground level enhancements on 14 July 2000 and on 13 December 2006 using neutron monitor data

On the basis of neutron monitor data we estimate the energy spectrum, anisotropy axis direction and pitch-angle distribution of solar energetic particles during two major ground level enhancements (GLE 59 on 14 July 2000 and GLE 70 on 13 December 2006). For the analysis we use a newly computed neutron monitor yield function. The method consists of several consecutive steps: definition of the asymptotic viewing cones of neutron monitor stations considered for the data analysis by computations of cosmic ray particles propagation in a model magnetosphere with the MAGNETOCOSMICS code; computation of the neutron monitor model responses and derivation of the solar energetic particle characteristics on the basis of inverse problem solution. The pitch-angle distribution and rigidity spectrum of high-energy protons are obtained as function of time in the course of ground level enhancements. A comparison with previously reported results is performed and reasonable agreement is achieved. A discussion of the obtained results is included as well their possible application is included.

physics.space-ph↗

arXiv2006

Neutron and Muon Flux Measurements at BEO Moussala towards to Space Weather Research

The existing and in development devices at Basic Environmental Observatory (BEO) Moussala are presented, precisely the experiments connected with space weather and astroparticle studies. The recent results of the secondary cosmic ray measurements using atmospheric Cherenkov light telescope are presented precisely the possibility to study the atmospheric transparency. The final design of neutron flux meter based on SNM-15 detectors is described as well several preliminary experimental and Monte Carlo results. The developed muon telescope based on water Cherenkov detectors is also presented. The scientific potential is discussed, precisely the connection between cosmic ray measurements and the environmental parameters, precisely atmospheric parameters. The project for muon hodoscope and multidirectional Nor Amberd neutron monitor with the preliminary studies is shown, precisely several estimations and the possible design

physics.space-ph↗

arXiv2006

Possible correlation between cosmic ray variation and atmosphere parameters (present status and future activities at BEO Moussala and Alomar observatory)

In this revue are presented several present activities and experiments at Alomar observatory and BEO Moussala and the possibility to investigate the influence of cosmic ray on climate parameters and the impact of cosmic ray to climate change. The general aim of these experiments is to study the possible correlation between cosmic ray variation and atmosphere parameters. The potential to study the possible correlations is discussed. The existing experiments and devices are presented as well these in preparation and commissioning. The scientific potential of future and in preparation experiments is discussed. The possibility to study the space weather at BEO Moussala and Alomar observatory presented. The specific devises precisely the muon telescope, neutron flux-meter, Cherenkov light telescope and muon hodoscope are presented

physics.space-ph↗

arXiv2005

Approximation of lateral distribution of atmospheric Cherenkov light at different observation levels for different primary particles. Applications for cosmic ray studies

This work summarizes the results presented at 29th International Cosmic Ray Conference in Pune India. Generally the aim of this work is to obtain the lateral distribution of the atmospheric Cherenkov light in extensive air showers produced by different primary particles in wide energy range and at several observation levels and to fit the obtained lateral distributions. Using one large detector and partially modified CORSIKA code version are obtained the lateral distributions of Cherenkov light flux densities at several observation levels for different particle primaries precisely at 536 g/cm2 Chacaltaya, 700 g/cm2 Moussala and 875 g/cm2 Kartalska field observation levels for hadronic primaries and gamma quanta in the energy range 1011 eV-1016 eV. On the basis of the solution of over-determined inverse problem the approximation of these distributions is obtained. The same model function for all the primaries is used and for the different observation levels. The different model parameters for the different primaries and levels are obtained. The approximations are compared with polynomial approximation obtained with different method. Both approximations are used for detector efficiency estimation for the different experiments in preparation and estimation of the accuracy of the reconstruction techniques. At the same time inclined showers up to 30 degrees zenith angle are studied at Chacaltaya observation level. The obtained lateral distributions of vertical showers are compared with vertical showers model and the previously obtained approximation. This permits to adjust the reconstruction strategy and to study the model parameters behavior.

astro-ph↗