Proton Events Research Articles

Features of Radio Signal Propagation in the VLF Range at High Latitudes during Solar Proton Events

Features of Radio Signal Propagation in the VLF Range at High Latitudes during Solar Proton Events

Subunit gating resulting from individual protonation events in Kir2 channels

Inwardly rectifying potassium (Kir) channels open at the ‘helix bundle crossing’ (HBC), formed by the M2 helices at the cytoplasmic end of the transmembrane pore. Introduced negative charges at the HBC (G178D) in Kir2.2 channels forces opening, allowing pore wetting and free movement of permeant ions between the cytoplasm and the inner cavity. Single-channel recordings reveal striking, pH-dependent, subconductance behaviors in G178D (or G178E and equivalent Kir2.1[G177E]) mutant channels, with well-resolved non-cooperative subconductance levels. Decreasing cytoplasmic pH shifts the probability towards lower conductance levels. Molecular dynamics simulations show how protonation of Kir2.2[G178D], or the D173 pore-lining residues, changes solvation, K+ ion occupancy, and K+ conductance. Ion channel gating and conductance are classically understood as separate processes. The present data reveal how individual protonation events change the electrostatic microenvironment of the pore, resulting in step-wise alterations of ion pooling, and hence conductance, that appear as ‘gated’ substates.

Incubation of protonated NADH or NADPH with ortho-aminobenzaldehyde generates a novel fluorescent nicotinamide dihydroquinazoline condensate

Incubation of reduced nicotinamide adenine dinucleotide (NADH) but not oxidized NAD+ with ortho-aminobenzaldehyde (oABA) generated an uncharacterized chromophore with an absorption peak characteristic of a dihydroquinazoline condensate. This chromophore is responsible for a non-specific signal in a diamine oxidase (DAO) activity assay based on the generation of fluorescent dihydroquinazoline structures directly from DAO substrates.Herein we show that at pH values below 3.0 the glycosidic bond of NADH/NADPH is broken releasing double protonated dihydro-nicotinamide (dihydro-NAM), which consequently condensates with oABA to a novel dihydroquinazoline chromophore and fluorophore, namely the 6- or 8-carbamoyl-5H,7H,8H,9H-10λ⁵-pyrido[2,1-b]quinazolin-10-ylium isomer (CMPQ). The second protonation event closely correlates with the pKa of the N1 nitrogen of C5-protonated dihydro-NAM and fluorophore stability. The fusion partner of oABA is likely the iminium of the primary acid product of dihydro-NAM after glycosidic bond hydrolysis and before irreversible cyclization.Trapping of protonated dihydro-NAM from NADH or NADPH with oABA allows quantification of these dinucleotides. Despite almost a century of research studying acid-catalyzed molecular rearrangements of NADH and NADPH, new and surprising details can be discovered.

Search for sources of solar cosmic rays in weak events

Some of the weak solar proton events recorded by the Earth observer, in which protons with energy E 10 MeV were observed, are really particles accelerated by a shock wave in interplanetary space. They can be associated with a flare and a coronal mass ejection ten of hours before the observed proton event, which ensure the injection of particles into the process of their subsequent acceleration in interplanetary space.

Geoefficiency of Sporadic Phenomena in Solar Cycle 24

The specific features of solar cycle 24 are discussed, including cosmic ray variations, characteristicsof solar flares, proton events, coronal mass ejections, and the level of geomagnetic activity. It is shownthat in terms of the sunspot number and other manifestations of solar activity, cycle 24 turned out to be themost modest one over the last 100 years of observations. A significant decrease in the geoefficiency of varioussolar events is described, which manifested itself in a smaller number and magnitude of Forbusheffects recorded on the Earth, the enhancements of the fluxes of protons and electrons of different energies,and geomagnetic storms.

Characteristics of Solar Proton Events during Periods of the Reversal of the Sun’s Magnetic Field over the Last Six Solar Cycles

Characteristics of Solar Proton Events during Periods of the Reversal of the Sun’s Magnetic Field over the Last Six Solar Cycles

Solar Proton Events and Forbush Decreases with the Same Sources

Solar Proton Events and Forbush Decreases with the Same Sources

Characteristics of solar proton events during the periods of Sun’s magnetic field reversal in the last 6 solar cycles

Characteristics of solar proton events during the periods of Sun’s magnetic field reversal in 19–24 solar activity cycles have been considered. In each of these solar cycles periods of time with duration of 8–12 months have been found, during which the number of solar events, total and maximal proton fluences were lower and the energy spectra were softer, than during the periods of equal duration before and after that. In most of the considered cycles the mentioned periods occurred after the cycle maximum or during the local “Gnevyshev minima”.

Solar relativistic electrons and protons on October 28, 2021 (GLE73)

The proton event of October 28, 2021, which was accompanied by the first in the current 25th cycle and the 73rd in the history of observations, a ground-based enhancement in the intensity of cosmic rays (GLE73), is considered. The development of the parent flare lasted more than 10 min against the background of the highest energy release simultaneously creating the conditions both for acceleration of the coronal mass ejection (CME) and acceleration of charged particles to relativistic energies. The similarity of time intensity profiles of relativistic electrons and protons in the Earth’s orbit indicates a stochastic mechanism of their acceleration. The X1.0 eruptive flare on October 28, 2021, is similar in hard X-ray emission to the M5.1 flare on May 17, 2012 (GLE71). The relatively late start of the increase in the fluxes of relativistic electrons and protons in the Earth’s orbit compared to the GLE71 event is explained by the location of the flare on October 28, 2021 (S26W05) and the southward launch of the CME.

Isolated Solar Cosmic Ray Events Caused by Energetic Storm Particles (ESPs)

Based on the catalogs of solar proton events for the 23rd and 24th solar cycles, events were chosenthat lacked a reliable source of particles but were accompanied by interplanetary and geomagnetic disturbances.As a rule, these events involve small proton fluxes that are detected near the Earth. All of the selectedevents occurred during the arrival of shock waves to the Earth, suggesting that they were likely caused by thearrival of energetic storm particles. It has been shown that flares accompanied by coronal mass ejections,which occurred tens of hours before the onset of the increase in particle fluxes in Earth’s orbit, could be thesource of these events. The selected events exhibited several specific features. Only one of them was accompaniedby a single shock front, while the others had two or three shock waves. The time profile of the eventsresembled a structure bounded by two shock fronts, suggesting that the shock waves likely accelerated andconfined the particles within a limited region of space.

Features of Radio Signal Propagation in the VLF Range at High Latitudes during Solar Proton Events

In this paper, we study the amplitude and phase characteristics of VLF signals of an anthropogenicorigin during solar proton events using the methods of a computational experiment. We consider the events ofOctober 30, 2003 and January 23, 2012. Electron density profiles are plotted using data from the VHF EISCATincoherent scatter radar located in Tromsø, Norway. Based on the processed data of computational experiments,that under the conditions of solar proton events, mainly amplitude distortions of VLF signals wereshown to be observed while there is a frequency dependence of the magnitude of distortions of the signals ofthe RSDN-20 long-range navigation radio system. The signal phases of the RSDN-20 system are less affectedby weak solar proton events. The effect of the lower boundary of the Earth-ionosphere waveguide in the casesof propagation of signals from the RSDN-20 system over the surface of land and ocean during a solar protonevent was studied.

Subunit gating resulting from individual protonation events in Kir2 channels

Subunit gating resulting from individual protonation events in Kir2 channels

Subunit gating resulting from individual protonation events in Kir2 channels

Subunit gating resulting from individual protonation events in Kir2 channels

Effect of solar proton events on test mass for gravitational wave detection in the 24th solar cycle

Free-falling cubic Test Masses (TMs) are a key component of the interferometer used for low-frequency gravitational wave (GW) detection in space. However, exposure to energetic particles in the environment can lead to electrostatic charging of the TM, resulting in additional electrostatic and Lorentz forces that can impact GW detection sensitivity. To evaluate this effect, the high-energy proton data set of the Geostationary Operational Environmental Satellite (GOES) program was used to analyze TM charging due to Solar Proton Events (SPEs) in the 24th solar cycle. Using the Geant4 Monte Carlo toolkit, the TM charging process is simulated in a space environment for SPEs falling into three ranges of proton flux: (1) greater than 10 pfu and less than 100 pfu, (2) greater than 100 pfu and less than 1000 pfu, and (3) greater than 1000 pfu. It is found that SPEs charging can reach the threshold within 535 s to 18.6 h, considering a reasonable discharge threshold of LISA and Taiji. We demonstrate that while there is a somewhat linear correlation between the net charging rate of the TM and the integrated flux of ge 10 MeV SPEs, there are many cases in which the integrated flux is significantly different from the charging rate. Therefore, we investigate the difference between the integral flux and the charging rate of SPEs using the charging efficiency assessment method. Our results indicate that the energy spectrum structure of SPEs is the most important factor influencing the charging rate. Lastly, we evaluate the charging probability of SPEs in the 24th solar cycle and find that the frequency and charging risk of SPEs are highest in the 3rd, 4th, 5th, 6th, and 7th years, which can serve as a reference for future GW detection spacecraft.

The 17 April 2021 widespread solar energetic particle event

Context.A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s−1that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min.Aims.We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons.Methods.We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes.Results.A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event.Conclusions.In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110° covered by distinct SEP injections, which is also supported by our SEP transport modeling.

Coronal Propagation of Solar Protons during and after Their Stochastic Acceleration

Solar protons in eruptive flares are stochastically accelerated in a wide spatial angle, and then they are effectively kept behind the expanding coronal mass ejection (CME) front, which can either bring protons to the magnetic-field line going to a remote observer or carry them away. We consider 13 solar proton events of cycle 24 in which protons with energy E 100 MeV were recorded and were accompanied by the detection of solar hard X-ray (HXR) radiation with E 100 keV by an ACS SPI detector and γ-radiation with E 100 MeV by the FermiLAT telescope with a source in the western hemisphere of the Sun. The first arrival of solar protons into the Earth’s orbit was determined in each event by a significant “proton” excess over the ACS SPI background during or after the HXR burst. All events were considered relative to our chosen zero time (0 min) of parent flares. The “early” arrival of protons to the Earth’s orbit (+20 min), which was observed in four events, corresponds to the “fast” acceleration of electrons (10 MeV/s). The “late” arrival of protons (+20 min) corresponds to the “slow” acceleration of electrons (1 MeV/s) and was observed in six events. In three events, a “delayed” arrival of protons (+30 min) was observed, when the CME propagation hindered the magnetic connection of the source with the observer. The direction of CME propagation is characterized in the catalog (SOHO LASCO CME Catalog) by the position angle (PA). The observed PA systematizes the times of the first arrival of protons and the growth rate of their intensity. The PA parameter should be taken into account in the analysis of proton events.

The Northern and Southern Hemispheric Asymmetries of Mesospheric Ozone at High Latitudes During the January 2012 Solar Proton Events

AbstractObservations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and simulations by the Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) are used to analyze the impacts of the January 2012 solar proton events (SPEs) on mesospheric ozone at high latitudes. The mesospheric ozone at high latitudes decreased evidently with the increasing proton flux and ionization rates during SPEs. The results of SABER and WACCM‐X both showed that maximum mesospheric ozone depletion reached 100% in the North Hemispheric (NH) high latitudes during SPEs while only 40% in the South Hemispheric (SH) high latitudes. The SPEs‐caused ozone changes simply occurred below 85 km and the ozone changes observed by SABER above 85 km may be associated with day‐to‐day variations. WACCM‐X simulations showed NOx (N, NO, and NO2) increased over 600% in both the northern and southern high latitudes during SPEs, while HOx (H, OH, and HO2) increased over 300% in the NH high latitudes and only over 30% in the SH high latitudes. HOx is the main ozone‐depleting substance because the reactions of NOx are less capable of depleting ozone than the reactions of HOx. Due to the difference in sunlight between the northern and southern hemispheres, ozone, HOx, and NOx exhibited significant northern and southern hemispheric asymmetries. Meanwhile, an increase in ozone after the SPEs was reported but not explained by previous studies. Here it is shown that the decreases in the HOx caused the increases in ozone after the SPEs.

Radioprotection for Astronauts' Missions: Numerical Results on the Nomex Shielding Effectiveness.

Space missions with humans expose the crews to ionizing radiation, mainly due to the galactic cosmic radiation (GCR). All radiation protection programs in space aim to minimize crews' exposure to radiation. The radiation protection of astronauts can be achieved through the use of shields. The shields could serve as a suit to reduce GCR exposure and, in an emergency, as a radiation shelter to perform necessary interventions outside the space habitat in case of a solar proton event (SPE). A space radiation shielding that is suitable for exploration during space missions requires particular features and a proper knowledge of the radiation type. This study shows the results of numerical simulations performed with the Geant4 toolkit-based code DOSE. Calculations to evaluate the performance of Nomex, an aramidic fiber with high mechanical resistance, in terms of dose reduction to crews, were performed considering the interaction between protons with an energy spectrum ranging from 50 to 1100 MeV and a target slab of 20 g/cm2. This paper shows the properties of secondary products obtained as a result of the interaction between space radiation and a Nomex target and the properties of the secondary particles that come out the shield. The results of this study show that Nomex can be considered a good shield candidate material in terms of dose reductions. We also note that the secondary particles that provide the greatest contribution to the dose are protons, neutrons and, in a very small percentage, α-particles and Li ions.

Radiation Aspect of Two Orbit Inclination Options of the Russian Orbital Service Station

The contribution to the effective dose from cosmic radiation of the Earth’s radiation belts, galactic cosmic rays, and solar proton events for astronauts located in the large-diameter working compartment of the service module of the ISS is considered. It is shown that for quasi-stationary sources of cosmic radiation, a change in the orbital inclination of 51.6° by 97.0° does not lead to significant variations in the average daily effective dose rate. When considering the contribution to the effective dose from solar-flare protons, the dose load on astronauts can increase by ten or more times.

A vibrational spectroscopic approach to elucidate the molecular mechanism behind the channel activity of viroporins.

The prevalence of diseases caused by pathogenic viruses and the scarcity of treatment and vaccination options call for extensive research of the molecular mechanisms underlying the function of these viruses. Small hydrophobic viral proteins with ion channel activity, so-called viroporins, are involved in the virus particle entry into and release from the host cell. One of these viroporins, the Influenza A M2 channel, has shown to be the target for anti-viral drugs motivating spectroscopic investigations of other viroporins to understand their relevance as potential anti-viral treatment targets. We used the Influenza A M2 viroporin as a model system to establish a vibrational spectroscopic approach to examine the gating mechanism and proton conductance of this pH-activated proton channel. In this work, we immobilized reconstituted M2 on a self-assembled monolayer bound to a nanostructured gold film that can be used for surface-enhanced infrared absorption (SEIRA) spectroscopy. Employing pH-induced SEIRA difference spectroscopy we monitor protonation events and changes in the α-helix amide I absorption due to a pH-dependent channel opening that leads to proton conductivity. Furthermore, the surface selection rule of SEIRA enabled us to observe the reorientation of the α-helical structures associated with the channel opening in-situ. Combining the spectroscopic data with computational vibrational spectroscopic calculations we model the large-scale reorganization of M2's α-helices, and by this quantify the opening angle of the channel transitioning from closed to the activated state. We aim to utilize this approach to enable a combined structural and functional analysis of viroporins of current relevance.