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An unusual solar event involving the detection of a He-3/He-4 ratio of about 1.5 was observed with the aid of the cosmic-ray telescopes of OGO-V on May 28, 1969. A theory dealing with the production of H-2, H-3, and He-3 in solar events is considered together with the conditions which would have to be satisfied in order to explain the observed very high helium isotope ratio in terms of the theory.
Multipoint spacecraft observations provide unique opportunities to constrain the propagation and evolution of interplanetary coronal mass ejections (ICMEs) throughout the heliosphere. Using Mars Global Surveyor (MGS) data to study both ICME and solar energetic particle (SEP) events at Mars and OMNI and Geostationary Operational Environmental Satellite (GOES) data to study ICMEs and SEPs at Earth, we present a detailed study of three CMEs and flares in late November 2001. In this period, Mars trailed Earth by 56deg solar longitude so that the two planets occupied interplanetary magnetic field lines separated by only approx.25deg. We model the interplanetary propagation of CME events using the ENLIL version 2.6 3-D MHD code coupled with the Wang-Sheeley-Arge version 1.6 potential source surface model, using Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) images to determine CME input parameters. We find that multipoint observations are essential to constrain the simulations of ICME propagation, as two very different ICMEs may look very similar in only one observational location. The direction and width of the CME as parameters essential to a correct estimation of arrival time and amplitude of the ICME signal. We find that these are problematic to extract from the analysis of SOHO/LASCO images commonly used for input to ICME propagation models. We further confirm that MGS magnetometer and electron reflectometer data can be used to study not only ICME events but also SEP events at Mars, with good results providing a consistent picture of the events when combined with near-Earth data.
Recent studies have proposed that the presence or absence of an interaction with a preceding coronal mass ejection (CME) or other coronal structure within approximately 50R(sub s), of the Sun discriminates large, fast CMEs associated with major solar energetic particle (SEP) events from those that are not. We conclude that there is no compelling evidence that, if such interactions take place, they play an important role in SEP acceleration. Reasons include: The reported statistical results are consistent with a chance association between interacting CMEs and SEP events; Energetic SEPs are detected at Earth typically before or around the time when the primary CME enters the LASCO C2 field of view - interactions higher in the corona cannot play a role in acceleration of these particles; For approximately 60% of major SEP events in 1997-2001, the preceding CME fades into the background corona or is relatively narrow (less than 40 deg), suggesting any interaction will be weak; Radio signatures attributed to CME interaction occur after SEP acceleration has commenced.
In this work we discuss the growing ensemble of solar particle events registered on the Martian surface, including their temporal appearance and solar sources. Solar energetic particle events from the surface of Mars have been observed starting soon after the August 2012 landing of the Radiation Assessment Detector onboard Curiosity. The Martian atmosphere prevents protons and heavy ions of up to 180 MeV/n kinetic energy from directly reaching the Martian surface. This cut-off is high enough to limit the number of solar energetic particle events measured on the surface to only 15 in ~12 ½ years. Yet we find in this analysis that Mars ground level enhancements follow the distinct SEP clock pattern as proton events observed at lower energies as reported in Posner, Richardson and Strauss (2024). Proton acceleration occurs predominantly near the solar surface, while transport to Mars incurs a delay in onset, and, as we show here, peak, that is a function of the longitudinal magnetic connection distance. between the foot point of solar wind magnetic field lines that intersect the Mars environment with the source longitude of the solar magnetic eruption. A distinct clustering of relative solar source locations at or near the Mars foot points at the Sun’s western limb is apparent, indicating lower flux thresholds from such preferred locations. Our findings have implications for astronaut safety at Mars.
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Previous studies using Skylab and Solwind coronagraph observations have shown that almost all E greater than 10 MeV solar energetic proton (SEP) events are associated with the occurrence of a coronal mass ejection (CME). These earlier studies did not address the relationship between the position of the associated CME and the timing of the injection of particles into the interplanetary medium. Ten cases are selected in which a SEP event observed with the GSFC detectors on the IMP 8 or ISEE 3 spacecraft was correlated to a CME well observed by the Solwind coronagraph. The height of the leading edge of the CME is compared with the particle injection profiles for several energy ranges using the solar release times for the particles. The derived injection profiles are found to be increasing and sometimes reaching maximum while the associated CMEs are at heights of 2-10 Ro.
Passive radiation dosimeters were exposed aboard the Mir Orbital Station over a substantial portion of the solar cycle in order to measure the change in dose and dose equivalent rates as a function of time. During solar minimum, simultaneous measurements of the radiation environment throughout the habitable volume of the Mir were made using passive dosimeters in order to investigate the effect of localized shielding on dose and dose equivalent. The passive dosimeters consisted of a combination of thermoluminescent detectors to measure absorbed dose and CR-39 PNTDs to measure the linear energy transfer (LET) spectrum from charged particles of LET infinity H2O > or = 5 keV/micrometers. Results from the two detector types were then combined to yield mean total dose rate, mean dose equivalent rate, and average quality factor. Contrary to expectations, both dose and dose equivalent rates measured during May-October 1991 near solar maximum were higher than similar measurements carried out in 1996-1997 during solar minimum. The elevated dose and dose equivalent rates measured in 1991 were probably due to a combination of intense solar activity, including a large solar particle event on 9 June 1991, and the temporary trapped radiation belt created in the slot region by the solar particle event and ensuing magnetic storm of 24 March 1991. During solar minimum, mean dose and dose equivalent rates were found to vary by factors of 1.55 and 1.37, respectively, between different locations through the interior of Mir. More heavily shielded locations tended to yield lower total dose and dose equivalent rates, but higher average quality factor than did more lightly shielding locations. However, other factors such as changes in the immediate shielding environment surrounding a given detector location, changes in the orientation of the Mir relative to its velocity vector, and changes in the altitude of the station also contributed to the variation. Proton and neutron-induced target fragment secondaries, not primary galactic cosmic rays, were found to dominate the LET spectrum above 100 keV/micrometers. This indicates that in low earth orbit, trapped protons in the South Atlantic Anomaly are responsible for the major fraction of the total dose equivalent. c2002 Elsevier Science Ltd. All rights reserved.
The risk from exposure to radiation posed to space travelers outside the magnetic shielding provided by the geomagnetosphere will come from two sources: the slowly varying but low intensity high-energy galactic cosmic rays and the more intense predominantly low-energy protons from large solar particle events associated with magnetic disturbances originating sporadically on or within the solar surface during the active period of the 11-year solar cycle. The energy spectra of the protons in solar particle events are quite soft, with large numbers of low-energy protons and a rather steep decrease of the energy spectra with increasing energy. This allows for the possibility to provide, within the space vehicle or habitat, a well-shielded area sometimes called a "storm shelter" or "safe haven" where the travelers could gather during the largest particle events. Intensity risetimes on the order of half an hour or more and overall event durations of 1 to 2 days would make actively seeking a well-shielded shelter for the duration a distinct possibility. The high-energy and penetrating nature and relative constancy of the galactic cosmic rays, on the other hand, do not allow the use of highly shielded areas as a means of protection against them. The first question to answer becomes: what is the risk to human health from the galactic cosmic rays? We need to have a good idea of the answer to this question before we can address the problem of how to best protect human health or, indeed, whether any specific measures need to be taken.
The radial variation of the interplanetary propagation of solar cosmic rays is investigated on a grand scale by performing a statistical analysis of charged-particle data obtained by Pioneers 10 and 11 from launch to Jovian encounter (i.e., at distances of 1 to 5 AU). A numerical propagation model is adopted which includes diffusion, convection, and adiabatic deceleration, as well as a variable power-law diffusion coefficient. The study of solar particle events is carried out by analyzing individually each of five key parameters that are uniquely defined in each solar particle event: the time to maximum flux starting from the initial release at the sun, the anisotropy at the time to maximum flux, the flux at that time, the time width of the event at half the flux at the time to maximum, and the decay time. Combined results for the proton energy ranges from 3.4 to 5.2 MeV and 24 to 30 MeV are presented, the average radial diffusion coefficients between 1 and 5 AU are determined for each energy range, and it is found that the combination of a near-impusive injection with a temporally constant spectral index produces a reasonably good fit to the high-energy data but not as good a fit to the low-energy data. Implications of the results obtained are discussed for cosmic-ray propagation theory, solar modulation studies, and interplanetary acceleration of solar particles.
A strategic focus area for NASA is to pursue the development of technologies which support exploration in space beyond the current inhabited region of low earth orbit. An unresolved issue for crewed deep space exploration involves limiting crew radiation exposure to below acceptable levels, considering both solar particle events and galactic cosmic ray contributions to dosage. Galactic cosmic ray mitigation is not addressed in this paper, but by addressing credible, easily implemented, and mass efficient solutions for the possibility of solar particle events, additional margin is provided that can be used for cosmic ray dose accumulation. As a result, NASA s Advanced Engineering Systems project office initiated this Radiation Storm Shelter design activity. This paper reports on the first year results of an expected 3 year Storm Shelter study effort which will mature concepts and operational scenarios that protect exploration astronauts from solar particle radiation events. Large trade space definition, candidate concept ranking, and a planned demonstration comprised the majority of FY12 activities. A system key performance parameter is minimization of the required increase in mass needed to provide a safe environment. Total system mass along with operational assessments and other defined protection system metrics provide the guiding metrics to proceed with concept developments. After a downselect to four primary methods, the concepts were analyzed for dosage severity and the amount of shielding mass necessary to bring dosage to acceptable values. Besides analytical assessments, subscale models of several concepts and one full scale concept demonstrator were created. FY12 work terminated with a plan to demonstrate test articles of two selected approaches. The process of arriving at these selections and their current envisioned implementation are presented in this paper.
There are three main sources of radiation in free space. These are the trapped protons and electrons, solar energetic particles, and the galactic cosmic rays. For human mission to Mars or moon, the trapped protons and electrons are of a minor concern. The flux of trapped particles at a fixed spacecraft altitude, and of galactic cosmic rays, decreases as the solar activity increases; however, the probability of a solar particle event increases as the solar activity increases. As these particles interact with the shielding material of the spacecraft and human body, they produce secondary particles, such as lighter fragments, target fragments, and neutrons. These particles can have far more damaging effect on cells than the primary particles. Thus, the radiation environment is very complex and varies with time. In this paper, we review the sources of charged-particles that contribute significantly to radiation risk to the astronauts, and estimates of exposure for some typical missions, such as Space Shuttle, International Space Station, and a human mission to Mars.
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Atmospheric ionizing radiation is produced by extraterrestrial radiations incident on the Earth's atmosphere. These extraterrestrial radiations are of two sources: ever present galactic cosmic rays with origin outside the solar system and transient solar particle events that are at times very intense events associated with solar activity lasting several hours to a few days. Although the galactic radiation penetrating through the atmosphere to the ground is low in intensity, the intensity is more than two orders of magnitude greater at commercial aircraft altitudes. The radiation levels at the higher altitudes of the High Speed Civil Transport (HSCT) are an additional factor of two higher. Ionizing radiation produces chemically active radicals in biological tissues that alter the cell function or result in cell death. Protection standards against low levels of ionizing radiation are based on limitation of excess cancer mortality or limitation of developmental injury resulting in permanent damage to the offspring during pregnancy. The crews of commercial air transport operations are considered as radiation workers by the EPA, the FAA, and the International Commission on Radiological Protection (ICRP). The annual exposures of aircrews depend on the latitudes and altitudes of operation and flight time. Flight hours have significantly increased since deregulation of the airline industry in the 1980's. The FAA estimates annual subsonic aircrew exposures to range from 0.2 to 9.1 mSv compared to 0.5 mSv exposure of the average nuclear power plant worker in the nuclear industry. The commercial aircrews of the HSCT may receive exposures above recently recommended allowable limits for even radiation workers if flying their allowable number of flight hours. An adequate protection philosophy for background exposures in HSCT commercial airtraffic cannot be developed at this time due to current uncertainty in environmental levels. In addition, if a large solar particle event occurs during flight at HSCT altitudes then passengers and crew may greatly exceed allowable limits unless means are available to reduce exposures.
We analyzed the coronal mass ejections (CMEs), flares, and type 11 radio bursts associated with a set of six low frequency (<14 MHz) extended type III bursts from active region 10588. The durations were measured at 1 and 14 MHz using high resolution data from Wind/WAVES and were within the range (>15 min) normally used to define these bursts. All but one of the type III bursts was not associated with a type 11 burst in the metric or longer wavelength domains. The burst without type 11 burst also lacked a solar energetic particle (SEP) event at energies >25 MeV. The 1-MHz duration of the type III burst (28 min) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. The CMEs were of similar speeds and the flares are also of similar size and duration. This study suggests that the type III burst duration may not be a good indicator of an SEP event.
The paper reports a statistical study of published intensity-time profiles of proton and electron solar particle events from 1967 to 1974. The purpose of the study was to examine systematically the temporal and rigidity dependence of the interplanetary scattering mean free path from approximately 1000 to 3000 MV. The observed t-max, the time from release of particles at the sun to the time of maximum flux at the spacecraft, were interpreted in terms of a propagation model to obtain the average radial scattering mean-free path. This path (1) appears to be species independent when it is derived from proton and electron solar particle events, (2) varies less than a factor of 2 from solar maximum to solar minimum, and (3) is nearly rigidity independent below approximately 500 MV. The path values obtained at low rigidities are inconsistent with path values derived theoretically from the interplanetary magnetic field fluctuations.
A summary is given of recent results from the direct determination of the charge states of He, C, O, and Fe. These results are used in discussing compositional variations during individual solar particle events. It is shown that ratio changes by a factor of approximately 10 during the onset phase of solar particle events can be explained not only by rigidity-dependent interplanetary propagation but also by rigidity-dependent diffusive propagation in the corona. Increasing experimental evidence is seen that other processes, such as compositional variations at the source and discontinuities of the interplanetary magnetic field separating two different particle populations, may be important. No common explanation is seen for all the variations, and it is concluded that each must be investigated on its own.
Epithermal Neutron Detector (FREND). Here we present results from measurements of the charged particle fluxes, dose rates and estimation of dose equivalent rates at ExoMars TGO Mars science orbit, provided by Liulin-MO from May 2018 to June 2022. The period of measurements covers the declining and minimum phases of the solar activity in 24th solar cycle and the rising phase of the 25th cycle. Compared are the radiation values of the galactic cosmic rays (GCR) obtained during the different phases of the solar activity. The highest values of the dose rate and flux from GCR are registered from March to August 2020. At the minimum of 24th and transition to 25th solar cycle the dose rate from GCR is 15.9 ± 1.6 µGy h−1, particle flux is 3.3 ± 0.17 cm−2 s−1, dose equivalent rate is 72.3 ± 14.4 µSv h−1. Since September 2020 the dose rate and flux of GCR decrease. Particular attention is drawn to the observation of the solar energetic particle (SEP) events in July, September and October 2021, February and March 2022 as well as their effects on the radiation environment on TGO during the corresponding periods. The SEP event during15–19 February 2022 is the most powerful event observed in our data. The SEP dose during this event is 13.8 ± 1.4 mGy (in Si), the SEP dose equivalent is 21.9 ± 4.4 mSv. SEP events recorded in Mars orbit are related to coronal mass ejections (CME) observed by SOHO and STEREO A coronagraphs. Compared are the time profiles of the count rates measured by Liulin-MO, the neutron detectors of FREND and neutron detectors of the High Energy Neutron Detector (HEND) aboard Mars Odyssey during 15–19 February 2022 event. The data obtained is important for the knowledge of the radiation environment around Mars, regarding future manned and robotic flights to the planet. The data for SEP events in Mars orbit during July 2021-March 2022 contribute to the details on the solar activity at a time when Mars is on the opposite side of the Sun from Earth.
The causal association of major solar particle events seen at earth with coronal mass ejections (CME's), and not with solar flares, is discussed. Evidence that led to the demise of the flare dominated paradigm for major solar energetic particle events are described. The possibility of distinguishing particles from impulsive and gradual events using only observations is described. Particle acceleration at the CME level is discussed. Multi-spacecraft observations of CME events are described. Concerning the interplanetary CME, bidirectional proton events are discussed. Conclusions from progress in understanding the characteristics of solar energetic particles and their relation to the physical mechanisms of acceleration are given.