MeV Proton Flux Research Articles

10.1007/s11208-008-1008-x

The solar flare of November 4, 2001, at 16.03–16.57 UT (GOES soft X-ray class X1.0, optical importance 3B, and coordinates N06W180) is used as an example to investigate the relationship between sporadic VHF radio bursts and charged particle fluxes (of both solar and magnetospheric origins) at an altitude of 500 km. The radio background intensity was recorded at frequencies of 280, 300, 151, and 500 MHz by nondirectional ground-based mid-latitude radio antennas spaced ∼700 km apart. The results of our radio measurements are compared with the dynamics of 0.2–12 MeV electron and 1–5 MeV proton fluxes based on data from the MKL instrument onboard the CORONAS-F satellite (the orbit altitude and inclination are 500 km and 82.5°, respectively).

GRADUAL SOLAR ENERGETIC PARTICLE EVENT ASSOCIATED WITH A DECELERATING SHOCK WAVE

On 2000 April 4-6 the Energetic and Relativistic Nuclei and Electron particle telescope on the Solar and Heliospheric Observatory spacecraft observed a major solar energetic particle (SEP) event associated with two coronal mass ejections (CMEs) separated by approximately 8 hr. The first CME was accompanied by a low-frequency type II radio burst observed by the WAVES receivers on the Wind spacecraft. Analysis of the high-precision measurements of the {approx}20 MeV proton flux anisotropy, model fitting of the type II dynamic spectrum, and SEP transport modeling support the idea that the shock wave of the first CME was an efficient accelerator for {approx}20 MeV protons during only the first 6 hr after the launch. This shock gradually slowed down, weakened, and became transparent for the protons produced by the second eruption behind the previous CME. The main production of SEPs due to the two successive eruptions continued together for 12 hr. The near-Earth SEP event was additionally amplified by the SEP mirroring in the interplanetary magnetic field draping at the edge of an old CME beyond the Earth's orbit, which made the SEP intensity-time profiles more prolonged than would be expected based on the assumption of SEP transport in the standardmore » solar wind.« less

The effects of hard‐spectra solar proton events on the middle atmosphere

The stratospheric and mesospheric impacts of the solar proton events of January 2005 are studied here using ion and neutral chemistry modeling and subionospheric radio wave propagation observations and modeling. This period includes three SPEs, among them an extraordinary solar proton storm on 20 January, during which the >100 MeV proton fluxes were unusually high, making this event the hardest in solar cycle 23. The radio wave results show a significant impact to the lower ionosphere/middle atmosphere from the hard spectrum event of 20 January with a sudden radio wave amplitude decrease of about 10 dB. Results from the Sodankylä Ion and Neutral Chemistry model predict large impacts on the mesospheric NOx (400–500%) and ozone (−30 to −40% NH, −15% SH) in both the northern (winter) and the southern (summer) polar regions. The direct stratospheric effects, however, are only about 10–20% enhancement in NOx, which result in −1% change in O3. Imposing a much larger extreme SPE lasting 24 hours rather than just 1 hour produced only about 5% ozone depletion in the stratosphere. Only a massive hard‐spectra SPE with high‐energy fluxes over ten times larger than observed here (>30 MeV fluence of 1.0 × 109 protons/cm2), as, e.g., the Carrington event of 1859 (>30 MeV fluence of 1.9 × 1010 protons/cm2), could presumably produce significant in situ impacts on stratospheric ozone.

Importance of predicting the dose temporal profile for large solar energetic particle events

It has been proposed that proton intensities on the stream‐limited plateau present a minimal radiation hazard to astronauts, and hazardous intensities occur upon coronal‐mass‐ejection‐driven shock arrival at the spacecraft. Forecasts then need only predict the arrival time and severity of the shock prior to its arrival at the spacecraft. We evaluated dose to the bone marrow, eye, and skin for the largest events since 1996, in terms of the >10 MeV proton flux, prior to and after shock arrival. Doses at shock arrival were compared to the space‐permissible exposure limits (SPELs), and for five of the seven events, limits were exceeded for aluminum shielding thicknesses up to 3 g cm−2 prior to the arrival of the shocks. The 30‐d SPELs have been exceeded as early as 9 h after event initiation, but more generally, sometime between 20 and 50 h after event initiation. These results suggest that one cannot simply predict the arrival time and intensity of a shock if exceeding the 30‐d SPELs is to be avoided. Similarly, waiting for the shock to arrive at a sentinel spacecraft such as the Advanced Composition Explorer to provide a 1‐h warning of shock intensity may not prevent one from exceeding the 30‐d SPELs. In order to predict when 30‐d SPELs will be exceeded for a given event, one must forecast the dose temporal profile associated with that event.

Search for the relationship between background VHF radio bursts and energetic particle dynamics based on data from the MKL instrument onboard the CORONAS-F satellite

The solar flare of November 4, 2001, at 16.03–16.57 UT (GOES soft X-ray class X1.0, optical importance 3B, and coordinates N06W180) is used as an example to investigate the relationship between sporadic VHF radio bursts and charged particle fluxes (of both solar and magnetospheric origins) at an altitude of 500 km. The radio background intensity was recorded at frequencies of 280, 300, 151, and 500 MHz by nondirectional ground-based mid-latitude radio antennas spaced ∼700 km apart. The results of our radio measurements are compared with the dynamics of 0.2–12 MeV electron and 1–5 MeV proton fluxes based on data from the MKL instrument onboard the CORONAS-F satellite (the orbit altitude and inclination are 500 km and 82.5°, respectively).

Electrochemical behaviour of gold and stainless steel under proton irradiation and active RedOx couples

Model experiments are reported where proton beams delivered by the cyclotron located at CERI (CNRS-Orléans) are used for irradiating AISI 316L/water and Au/water high purity interfaces with 6 MeV protons. The free exchange potentials at the interfaces are recorded as a function of time at room temperature in situ before, under, and after proton irradiation. The evolutions are compared to those calculated for the Nernst potentials associated with the radiolytic RedOx couples. It is shown how the comparison gives evidence that five radiolytic species – O 2 , H 2O 2, HO 2 −, HO 2 and O 2 − – exchange electrons at the Au interfaces in a range of dose rates that vary over three orders of magnitudes, i.e. 0.0048 < dr(10 7 Gy h −1) < 4.8. The balance between the electron exchanges at Au interfaces is adjusted by the RedOx reactions associated with the above species. The free exchange potential reaches the same steady value for Au and AISI 316L interfaces irradiated at high doses, ≥2.5 × 10 7 Gy, (0.020 ± 0.025) V versus NHE. Such low values are the first ones to be reported. The HO 2 and O 2 − radical disproportionations play a key role and control the potential at the interfaces under 6 MeV proton flux. This role is generally mostly overlooked for gamma irradiation.

Scanning an Interplanetary Magnetic Cloud Using High‐Energy Protons

We applied a numerical modeling of the solar energetic particle (SEP) event inside a magnetic cloud in the solar wind to analyze the 17-22 MeV proton flux anisotropy observed on 1998 May 2 with the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The analysis revealed a strong intermittency of the SEP transport parameters when different magnetic tubes were convected past the spacecraft. The estimated mean free path value varies over 1 order of magnitude, from ~2 to ~20 AU. The SEP event has been modeled with a prolonged injection of particles from a new CME into the previous ejecta comprising a set of magnetic loops. Both the prompt, direct proton flux and the delayed, counterstreaming flux were observed in the beginning and maximum phase of the event, but then the counterstreaming flux waned. The lack of counterstreaming protons can be explained either by the very fast escape of high-energy protons from the magnetic cloud, before they could complete one bounce in a narrow loop, or by the proton injection predominantly into one leg of a wide loop. An imprint of the magnetic compression at the leading part of the CME can be also found in the proton flux anisotropy data of SOHO/ERNE. These findings illustrate how high-precision anisotropy measurements and a numerical modeling can provide a kind of probe for the CME structure.

Destruction of the tertiary ozone maximum during a solar proton event

Ozone observations from the GOMOS instrument together with a coupled ion and neutral chemistry model are used to study the effects of the January 2005 solar storms on the polar winter middle atmosphere. The model results indicate strong HOx and NOx enhancements in the mesosphere, and simultaneous ozone depletion maximizing between 70–80 km. During strong proton forcing GOMOS measurements show the destruction of the tertiary ozone maximum, observed at polar latitudes near 72 km before the events. This altitude is concurrent with the largest HOx enhancements in the model results. We observe for the first time the disappearance of the tertiary ozone maximum, and determine the underlying cause. With subsiding proton forcing GOMOS measurements show the reappearance of the tertiary ozone maximum, returning to normal values by January 24. Our results indicate that even moderate solar events (&gt;10 MeV proton flux of &gt;5000 pfu) can cause significant ozone depletion (&gt;70%) in the middle atmosphere.

Evidence of Enceladus and Tethys microsignatures

We present evidence of two icy satellite microsignatures in the Cassini LEMMS data. Just upstream of Enceladus, a deep and narrow decrease in the flux of several MeV electrons is consistent with a recent absorption by that moon. This microsignature is collocated with a deep depletion in the MeV proton flux. The proton feature is much wider than the satellite diameter, suggesting multiple interactions and/or losses to the E Ring and neutral gas. An observed increase in proton flux toward the planet suggests a possible inner magnetospheric source. A decrease in the low energy electron intensity downstream of Tethys is also consistent with a microsignature approximately the size of the satellite that has drifted slightly toward the planet near midnight. Modeling suggests that microsignatures near Tethys' orbit would persist for more than a complete rotation of Saturn and the radial diffusion coefficient is about 10−9 RS2/s.

Modeling a large solar proton event in the southern polar atmosphere

We have modeled the effects of the Sodankylä Ion Chemistry model (SIC) electron density profiles on VLF propagation across the southern polar region during the first few days of the 4–10 November 2001 solar proton event (SPE). The results show that the SIC model is accurately reproducing the changes in ionization during the SPE. These results were obtained by approximating the SIC electron density profiles to the Wait β and h′ profiles where the densities were below 1000 el cm−3, a limitation that means during SPEs the technique is typically sensitive in the altitude range 50–60 km. The calculated values of β and h′ were applied to the part of the propagation path poleward of the L = 4 boundary for the Hawaii (NPM)–Halley great circle path. Comparing the change in amplitude of NPM at Halley during the SPE with the GOES satellite proton flux measurements, we observe a good correlation and thus conclude that the variability observed in the VLF data is primarily caused by &gt;50 MeV proton fluxes. This suggests that the SPE produced ionization dominates all other precipitation sources at these altitudes during 4 and 5 November 2001. Consequently, these results suggest that the assumption made during the SIC modeling runs of 4–5 November 2001 of only having proton precipitation and no significant energetic electron precipitation was reasonable. Our work strongly suggests that VLF subionospheric propagation is a reliable tool for the study of SPEs and that it is particularly effective when used in conjunction with an atmospheric model such as SIC.

The 1998 May 2-3 Magnetic Cloud: An Interplanetary "Highway" for Solar Energetic Particles Observed with SOHO /ERNE

Using the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), we have measured the 17-22 MeV proton flux anisotropy during the 1998 May 2-3 solar energetic particle (SEP) event, when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The ability of the SOHO/ERNE to measure particle fluxes with high angular resolution makes it a unique instrument for observing SEPs under weak scattering conditions. During most of the first 4 hr of the SEP event that started shortly after 14 UT on 1998 May 2, the proton intensity parallel to the magnetic field was ~1000 times higher than in the perpendicular direction. The ERNE observations indicate that the magnetic flux-rope structure of the CME provides a "highway" for transport of solar energetic protons with a parallel mean free path of at least 10 AU. The particle telescope ERNE/High Energy Detector was able to measure the proton angular distribution, which was narrow to an extent that it could not be resolved with other instruments. Within 30-45 minutes after the onset of the proton event, a counterstreaming flux was also identified. The ERNE data also revealed a narrow magnetic tube in which protons were much less anisotropic than in the rest of the rope. We briefly discuss the implications of these findings for the origin and structure of the CME.

Radioluminescence of alumina during proton and heavy ion irradiation

Radioluminescence (RL) of sapphire and polycrystalline alumina (p-Al 2O 3) under 8 MeV proton (flux 2 × 10 12 proton/cm 2s), 150 MeV argon (4.3 × 10 8 ion/cm 2 s) and 253 MeV krypton (4.3 × 10 8 ion/cm 2 s) ion irradiation has been measured in the UV and visible ranges. The processes causing the changes of RL of sapphire with a dose differ from those of p-Al 2O 3. Radiation-induced annealing of oxygen vacancies in p-Al 2O 3 occurs with decreasing F +-band. Inhomogeneous distribution of traps associated with grain boundaries causes electrical charging of microscopic regions in p-Al 2O 3 and an increase of F-band of RL. The accumulation of charge carriers at traps increases excitation probability of F +-center and results in growth of F +-band of sapphire. A ratio of initial to saturation intensity of the F +-band increases with increasing the linear energy loss of incident particles.

Ulysses observations of solar energetic particles from the 14 July 2000 event at high heliographic latitudes

At the time of the solar flare on the Bastille Day of 2000, the Ulysses spacecraft was at 3.17 AU from the Sun, 62° south in heliographic latitude, and 116° in longitude east of the Earth. Solar wind and magnetic field measurements by Ulysses indicate that the coronal mass ejection (CME) of this event had a limited size in both latitude and longitude, although it was a halo CME as seen in the Solar and Heliospheric Observatory coronagraph images. The event produced large fluxes of energetic particles up to energies &gt;100 MeV at both Ulysses and the Earth. Enhancements of energetic particles were immediately observed at the Earth, with their onset times consistent with the velocity dispersion due to the streaming of particles along magnetic field lines from the location of particle acceleration in the corona to the Earth. To the contrary, at Ulysses, the energetic particles from the solar event were not detected until 4–11 hours later, and the increases of particle intensity were much more gradual. The onset times of particles in different energy channels were not organized by particle speed; rather they depended on both particle rigidity and speed, indicating that the transport of particles to Ulysses at high latitudes had a diffusive nature. The first‐order anisotropy in the 40–90 MeV proton flux was significantly larger than what is expected from the Compton‐Getting effect for many hours after the onset. The direction of the first‐order anisotropy was not along the projection of local magnetic fields onto the scan plane of the detector and it was not affected by the polarity of the field either, indicating that the particles did not arrive at Ulysses through propagation along magnetic field lines and rather much of the anisotropy was produced by cross‐field diffusion in the presence of a cross‐field density gradient pointing toward the low latitude direction. All these observations are consistent with easy particles transport across the mean heliospheric magnetic fields. The apparent difficulty for the theory is that the observations require a cross‐field diffusion that is too fast to be explained by random walk of field lines due only to supergranulation.

In-flight observations of the radiation environment and its effects on devices in the SAC-C polar orbit

This paper presents particle flux measurements and single event effect (SEE) data obtained with Influence of Space Radiation on Advanced Components (ICARE) on the SAC-C orbit (707 km, 98.2/spl deg/) for the period November 2000-June 2002. An increase of 10 MeV proton flux in the belts is clearly observed and correlated to solar proton events associated with magnetic storms. SEU rate measurements are presented for SRAM and DRAM devices, and their response to solar events shows SEU rate increases (up to a factor of 115) correlated with high-energy protons (E/spl ges/84 MeV).

Cosmic rays activity and monthly number of deaths: a correlative study.

We studied the relation between the intensity of cosmic rays, the level of solar/geomagnetic activity, and the monthly numbers of deaths in a large hospital in Israel and in all Lithuania. The Israeli data include 30526 hospital deaths, two groups of fatal suicides (2359, 2763), and 15435 suicidal attempts for two periods of 108 and 236 consecutive months. The national data for the entire Republic of Lithuania include 424925 deaths for the period of 120 consecutive months. Cosmic rays intensity was measured by an Apatity neutron monitor. We obtained the data on solar, geomagnetic radiovawe propagation, ionosphere ionization hours, proton flux of two energy levels (>90 and 60 MeV) from the National Geophysical Data Center at Goddard Space Flight Center, National Space Environment Center at Boulder, Colorado, USA, and from the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Russia. We calculated Pearson coefficients and their probabilities for correlation between monthly space activity level and monthly number of male and female deaths from different causes. Cosmic rays activity revealed significant negative correlation with solar/geomagnetic activity indices and related physical phenomena levels. This activity strongly correlated with flux of protons with the energies >90 MeV proton flux and did not exhibit significant correlation with 60 MeV proton fluxes. Cosmic rays intensity correlation with monthly numbers of deaths was strong for noncardiovascular deaths, suicides, and traffic accidents. The correlation was much weaker for deaths caused by ishemic heart disease and strokes.

A relation between dynamics of coronal mass ejections and production of solar energetic particles

During January 1997-June 1998, the Large Angle Spectroscopic Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft (SOHO) registered 670 coronal mass ejections (CMEs). We compare two groups of the 300-800 km s-1 CMEs: (i) (very) gradually accelerating CMEs with acceleration below , and (ii) impulsively accelerating CMEs with acceleration near the Sun, continuing then with the constant speed across the LASCO field of view. An association of those CMEs with solar energetic particle (SEP) events is studied using the data of the energetic particle experiment ERNE also aboard SOHO. There were no SEP events registered in association with the first group CMEs, whereas about 8% of the second group CMEs produced an enhancement in the ~10 MeV proton flux at SOHO. This result along with a number of additional tests supports an idea that production of SEPs by the moderate speed CMEs depends not only on the final speed but also on the magnitude of acceleration that CME experiences during its liftoff. The SEP-producing CMEs are typified by impulsively accelerating CMEs accompanied by soft X-ray flares and coronal shocks.

Two-parametric representation of the solar and heliospheric protons

Abstract The dynamics of the interplanetary proton spectra in the energy range 1–40 MeV have been investigated using the data obtained on board the IMP-8 (1973–1992) and Meteor (1970–1996) satellites. Phase diagrams of the proton events are constructed in the two-parametric space { Y,g }, where Y=g −1 lg( I p ), g is the differential energy spectral index, I p represents the >1 MeV proton intensity. The results show that the phase trajectories allow separation of the background proton fluxes, proton populations accelerated mainly in the solar flares, at the propagating interplanetary shocks associated with coronal mass ejections and also in the corotating interaction regions between fast and slow solar wind streams. The estimations of the maximal and minimal >1 MeV proton fluxes in the near Earth heliosphere are obtained.

Energetic proton observations at 1 and 5 AU: 1. January–September 1997

We present energetic particle observations by the Ulysses and Wind spacecraft during the years 1997–1998. During this period, Ulysses moved from +19° to −19° in heliographic latitude with heliocentric distances ranging from 4.71 to 5.41 AU. Wind was located near the Earth at 1 AU from the Sun in the ecliptic plane. The proximity of Ulysses to the ecliptic plane allows us to compare proton fluxes at different heliospheric distances and heliolongitudes but at similar latitudes. Enhancements in the energetic (approximately MeV) MeV proton fluxes were observed by both spacecraft in a close temporal association. We quantify this temporal coincidence and we distinguish two time intervals based on the energy range of the proton flux increases and on the solar wind streams observed by the Ulysses spacecraft. Each one of these two periods (period 1, January–September 1997 and period 2, October 1997 to December 1998) corresponds also to a different level of solar activity. We establish a direct correspondence between individual particle flux enhancements observed by both spacecraft throughout period 1. At 1 AU the proton flux enhancements are associated with the occurrence of coronal mass ejections (CMEs) at the Sun. At 5 AU the presence of high‐speed solar wind streams, the contribution of energetic particles from CMEs, and the evolution of the magnetic field structures along which energetic particles propagate determine the final shape of the proton flux enhancements and their time delays with respect to 1 AU. When a solar energetic particle (SEP) event is observed at 1 AU, particle flux enhancements associated with recurrent high‐speed solar wind streams at ∼5 AU show a higher particle flux intensity. We suggest that SEPs accelerated by CME‐driven shocks act as a background seed particle population available to be reaccelerated by shocks associated with corotating high‐speed streams.

Changes in luminescence emission induced by proton irradiation: InGaAs/GaAs quantum wells and quantum dots

The photoluminescence (PL) emission from InGaAs/GaAs quantum-well and quantum-dot (QD) structures are compared after controlled irradiation with 1.5 MeV proton fluxes. Results presented here show a significant enhancement in radiation tolerance with three-dimensional quantum confinement. Some additional radiation-induced changes in photocarrier recombination from QDs, which include a slight increase in PL emission with low and intermediate proton doses, are also examined.

Correlation of two levels of space proton flux with monthly distribution of deaths from cardiovascular disease and suicide.

In our previous studies /1-3/ we described some significant links between monthly number of deaths due to cardiovascular disease and suicide and space proton flux > 90 MeV. The aims of the present study were to compare the relationship of some solar and geomagnetic parameters with space proton fluxes of > 60 and > 90 MeV; to examine the monthly correlation of these two proton groups with the monthly death distribution in two countries, Israel and Lithuania. Physical data were obtained from the National Geophysical Data Center and the SESC in Boulder, CO; NSSDC in Goddard Space Flight Center, USA, and the Izmiran Institute of the Academy of Sciences in Russia. Pearson correlation coefficients and probabilities were compared for 56-180 consecutive months. Proton flux of > 60 MeV significantly correlated with three of the four studied monthly geomagnetic activity indices (Ap, Am, Dst), but not with such solar activity markers as sunspot number and solar flux (2800 MGH, 10.6 cm). There was no significant relationship between proton flux of > 60 MeV and monthly number of deaths from cardiovascular diseases and suicide, in contrast to the results for > 90 MeV. From the data available during the 36 months (1986-1988), there was no correlation between monthly levels of > 60 to > 90 MeV. In conclusion, a monthly space proton flux of > 60 MeV is not significantly correlated with the monthly death distribution from cardiovascular disease and suicide and some solar activity indices, such as proton flux of > 90 MeV. It is possible that the 60-90 MeV fraction in the > 60 MeV proton flux "blunts" the cosmobiological relationship between proton flux of > 90 MeV and monthly death number.