Solar Particle Fluxes Research Articles

The detection of energetic cometary and solar particles by the EPONA instrument on the Giotto mission

EPONA is an energetic particle detector system incorporating totally depleted silicon surface barrier layer detectors. Active and passive background shielding will be employed and, by applying various techniques, particles of different species, including electrons, protons, alpha particles and pick-up ions of cometary origin may be detected over a wide spectrum of energies extending from the tens of KeV into the MeV range. The instrument can operate in two modes namely (a) in a cruise phase or storage mode and (b) in a real time mode. During the real time mode, observations at high spatial (octosectoring) and temporal (0.5s) resolution in the cometary environment permit studies to be made of accelerated particles at the bow shock and/or in the tail of the comet. In conjunction with magnetic field measurements on board Giotto, observations of energetic electrons and their anisotropies can determine whether the magnetic field lines in the cometary tail are open or closed. Further, the absorption of low energy solar particles in the cometary atmosphere can be measured and such data would provide an integral value of the pertaining gas and dust distribution. Solar particle background measurements during encounter may also be used to correct the measurements of other spacecraft borne instruments potentially vulnerable to such radiation. Solar particle flux measurements, obtained during the cruise phase will, when combined with simultaneous observations made by other spacecraft at different heliographic longitudes, provide information concerning solar particle propagation in the corona and in interplanetary space.

Solar radiation monitoring for high altitude aircraft.

Ground-based and satellite-based ionizing radiation monitoring systems are considered as alternative methods for ensuring safe radiation levels for high-altitude aircraft. It is found that ground-based methods are of limited accuracy due to insensitivity to solar particles of energies between the riometer upper cutoff of about 50 MeV and the neutron monitor threshold of about 450 MeV. This energy range is demonstrated to be essential for atmospheric radiation monitoring at high altitude, and must be covered by satellite measurement. On the basis of presently available data, the accuracy to which the incident solar particle flux must be measured by satellite-borne detectors is examined and recommendations are made to establish minimum requirements.

The elemental and isotopic composition of cosmic rays - Silicon to nickel

The reported observations were made with the aid of the Cosmic Ray Isotope Instrument System (CRISIS) which had been designed to detect and resolve the isotopes of cosmic ray nuclei with atomic numbers equal to or greater than 10. The CRISIS detector was flown on a balloon launched from Aberdeen, South Dakota on 1977 May 20. The period 1977 May 19-22 has been classified by Mason et al. (1979) as one of 'superquiet' solar activity, characterized by the lowest fluxes of low-energy solar particles ever observed. The obtained results are presented in a number of graphs and tables. It was found that the elemental and isotopic abundances of Si are solar-like. Elemental S is underabundant in the cosmic rays by a factor of approximately 3 relative to the solar system, but its isotopic composition resembles the solar composition with S-32 being the dominant isotope. Elemental Ar is virtually absent in the source, and the observed isotopic composition is consistent with a secondary origin. Elemental Ni has a solar-like abundance.

Martian climatic change: A magnetic trigger?

A new mechanism for climatic change on Mars involving interactions between the atmosphere and a hypothesized ancient planetary magnetic field is suggested and discussed. An early dynamo for Mars is not inconsistent with either current data on the martian interior, models of planet origin, or dynamo theory. The Jacobs/Busse scaling law suggests a martian dynamo field would have effectively shielded the atmosphere from the solar wind. Cooling and/or solidification of the core would cause dynamo extinction and expose the martian atmosphere to the full solar and galactic particle flux. These events may have triggered atmospheric cooling and the present martian frozen surface; as suggested by: (1) climatic records of the earth, and (2) current models of nucleation and other relevant atmospheric processes.

The spatial anisotropy, rigidity spectrum, and propagation characteristics of the relativistic solar particles during the event on May 7, 1978

The data from the worldwide network of neutron monitors have been used to deduce the spatial distribution, rigidity spectrum, and propagation characteristics of the GLE on May 7, 1978. The large magnitude of the GLE and hard rigidity spectrum enabled an analysis to be made utilizing both high‐latitude and mid‐latitude stations. A straightforward method of analysis could not be used to determine the source function, probably owing to the influence of external magnetospheric currents upon the asymptotic directions of high‐latitude neutron monitors and on the asymptotic directions of all stations at rigidities near cutoff. Consequently, we used measurements from the mid‐latitude neutron monitors sensitive to high rigidity particles from the solar flare. The apparent source of the solar particle flux near earth was located in a region around 20°N, 87.5°E, which is approximately 40° west of the sun. The functional form of the pitch angle distribution was given by exp (−δ²/2θ²), θ≈ 25° during the first 30 minutes and then became flatter. The observed anisotropy was ∼1 until 0410 UT, then decreased to <0.7 at 0430 UT when the enhancement of the counting rate was ≲10% of the maximum increase at neutron monitors that were ideally situated to observe the GLE. The rigidity spectrum for P >3 GV was an exponential exp (−P/Po) with Po=1.45 near the onset, changing to Po=0.7 GV later. An analysis using the telegraph equation [Fisk and Axford, 1969] yields a scattering mean free path λ∥≳3 AU. The analysis indicates that the propagation was scatter‐free for about one hour and that the intensity‐time profile of the solar injection was observed for particles with P >1 GV.

On the Climate-Radiocarbon Relationship: Nitric Oxide and Ozone as Connecting Links Between Radiation and the Earth's Surface Temperatures

The correlations between atmospheric radiocarbon cencentrations, on the one hand, and solar activity and the earth's magnetic field, on the other, as well as possible relations between surface temperatures and solar activity and the earth's magnetic field are considered. To draw a consistent picture of these relations, the following mechanisms for climatic changes are proposed: The earth's magnetic field and solar activity both influence the fluxes of charged solar particles into the upper stratosphere; higher surface temperatures are positively correlated with higher particles fluxes. Charged particles produce nitric oxide, which controls, to some extent, the ozone destruction and, thus, the ozone inventory in the upper layers of the stratosphere (above the 10 mbar level) in latitudes greater than about 60°. The varying ozone contents in the upper stratosphere affect the radiation balance and the temperatures on the earth's surface. It has been estimated that a reduction, or increase, respectively, of ozone in the layers above 10 mbar warms, or cools, respectively, the earth's surface. A change of ozone in the lower layers of the stratosphere has the opposite effect. The maximum net effect is in the order of ΔTs≈ 0.3–1 K, in both directions. This hypothesis might be in accordance with an orbital origin of long-term climatic changes.

Modulation of solar flare particles and track density profiles in gas-rich meteorite grains

A solution is presented to the problem concerning the time-averaged solar flare particle flux as a function of kinetic energy and distance from the sun for a given particle injection spectrum at the sun within the framework of standard diffusion-convection-adiabatic deceleration theory with the diffusion coefficient independent of distance from the sun. Results of the calculations which give best agreement with observations at 1 AU are presented and discussed, with particular reference to their implications for gas-rich meteorites. Normalization at the orbit of earth is achieved via observed track density versus depth profiles in lunar vug crystals. It is shown that if gas-rich meteorite grains were irradiated in the asteroid belt and if source and modulation parameters have changed little since irradiation, the track density should be 'harder' than the lunar vug profile by about 0.2-0.3 in the index. Quantitative estimation of solar flare particle exposure ages is discussed.

ATS-6 Energetic Particle Radiation Measurement at Synchronous Altitude

The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 MeV. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles.

Angular distributions of solar protons and electrons

High angular-resolution measurements of directional fluxes of solar particles in space have been obtained with detectors aboard OGO-5 during the cosmic ray event of 18 November 1968. This is the only case on record for which sharply-defined directional observations of protons and electrons covering a wide rigidity range (0.3 MV to 1.5 GV) are available. The satellite experiment provided data for determining pitch-angle distributions with respect to the direction of the local interplanetary magnetic field lines during the lengthy highly anisotropic phase of the event. It was found that the unidirectional differential intensities j( θ) of 3- to 25-MeV protons varied in accordance with the relationship j( θ) = b 0 + b 1 cos θ + b 2 cos 2 θ, where b 0 and b 1 ≳ 0, and b 2, is positive, zero or negative. Soon after onset, 79–266-keV electrons arriving from the direction of the Sun displayed an anisotropic component with the intensity varying as cos θ. Later, a double-peaked distribution appeared at the lower energies, whereas the flux at the upper end of the range covered by the experiment became isotropic. These results have been interpreted in the light of the temporal flux profiles and the state of the interplanetary medium. The observation of the unusually large and long-lasting anisotropies lead to several conclusions including: (1) If injection of the solar particles was instantaneous, the diffusion coefficient was either constant or increasing with distance from the Sun. (2) If the solar source emitted particles over an extended period, and there is evidence to that effect, there was weak scattering in the region between the Sun and the Earth and a strong scattering region beyond the Earth's orbit. (3) Solar electrons were stored near the Sun. (4) The observed angular distribution of 200-MV protons in the magnetosheath was in good agreement with that deduced in an earlier analysis of polar orbiting satellite observations and trajectory calculations.

Interplanetary acceleration of low-energy solar protons: A study of the solar particle event of November 18, 1968

The spectra of solar proton and alpha particle fluxes from the solar particle event of November 18, 1968, deviate considerably from a power law form for as long as 2 days after the onset of the event. The spectral distortions are observed to progressively diminish with time. The departures in the spectral shape are not entirely attributable to diffusive velocity dispersion of the solar particles. Several lines of possible interpretation, taking into consideration effects of particle storage in the corona and the acceleration and deceleration of particles in the interplanetary medium, are discussed. It is suggested that acceleration of solar protons and alpha particles in the interplanetary medium is perhaps occurring. The time scales for the acceleration of protons in the energy range 0.6–2.0 MeV are derived.

Action of Solar Particle Fluxes on the Lower Layers of the Earth's Atmosphere

Action of Solar Particle Fluxes on the Lower Layers of the Earth's Atmosphere

Variations of the trapped particle population and of cutoff and pitch angle distribution of simultaneously observed magnetospheric solar protons during substorm activity

The behavior of solar protons (1.5–2.7 MeV) and trapped electrons (>1.5 MeV) observed by a low-altitude polar-orbiting satellite (Azur) during the occurrence of an isolated substorm (March 29–30, 1970) is examined. Onset of the substorm is determined and its development is discussed by using energetic and high-energy particle data from the ATS 5 satellite. The comparison of equatorial and low-altitude electron data shows that the behavior of the trapped electron population is consistent with the adiabatic model given by Lezniak and Winckler (1970). Observation of an isotropic pitch angle distribution of the solar protons leads to the conclusion that there is evidence for strong pitch angle scattering of these particles in the pseudotrapping region. We also observed during the substorm a large change in the slope of the solar particle flux profile at cutoff that occurred simultaneously with a variation of the trapping boundary. It is suggested that this effect might explain the often observed ‘deep entry’ of solar protons into closed drift shells well below the nominal cutoff.

The Influence of Certain Ionoshperic Phenomena on Extremely Low Frequency (ELF) Propagation

A number of phenomena that may cause irregularities in extremely low frequency (ELF) ionospheric propagation are suggested. Geomagnetic anisotropy, path asymmetry due to different ionospheric characteristics on the darkened and sunlit hemispheres, effects of strong boundary discontinuities such as the twilight zone or northern latitude sporadic E , and the effects of geophysical trauma such as solar particle fluxes are considered. A primitive analysis of ELF propagation data illustrates that an association can be drawn between the effects of solar charged particle emissions and coincident ELF propagation irregularities. Paths that pass through the auroral zone appear to be most severely affected.

Anisotropies in relativistic cosmic rays from the invisible disk of the Sun

The most recent (September 1–2, 1971) of the rare ground level events signaling the arrival at the earth of relativistic solar cosmic rays arising from a flare on the sun's invisible hemisphere displayed marked anisotropy for several hours. Application of newly developed analytical procedures has made it possible to study in detail the evolution of the anisotropic pitch angle distribution. Throughout the anisotropic phase the solar particle flux is proportional to the cosine of the angle between the weighted mean asymptotic direction of viewing and an axis of symmetry corresponding to the spiral interplanetary magnetic field line that connects the sun to the earth. Furthermore, the degree of anisotropy deduced from the ratio of the fluxes in the garden hose direction toward and away from the sun decays exponentially. The results of this analysis and the reexamination of the three previously observed invisible hemisphere ground level events have demonstrated that propagation along the spiral interplanetary field line connecting the sun to the earth occurs even when the source lies far beyond the limb of the sun. In one case (January 28, 1967) the anisotropy near onset was 100% (i.e., no particles traveling toward the sun), a situation that had only been reported twice previously and then in association with visible flares that occurred within 10° of the foot of the nominal garden hose field line. These results bespeak the operation of an efficient transport mechanism in the solar corona that enables relativistic protons to travel over distances at least as great as 70° in heliolongitude in about 15 min.

Time dependent worldwide distribution of atmospheric neutrons and of their products: 3. Neutrons from solar protons

During solar particle events from 1968 to 1971 we observed increases in the fast neutron flux at high latitude and at 55- to 75-g/cm² atmospheric depth. The increases correlated with the variations in the solar proton fluxes; the neutron yield per incident proton, above threshold, increased by a factor of 100 with increasing hardness of the proton spectrum. Within a factor of 2 the neutron specific yield fell on a smooth curve versus the spectral parameter P0, where the values of P0 were based on the SPME (solar proton monitor experiment) data from Explorer 34 and 41. The neutron yield from solar particle events was calculated from a Monte Carlo simulation of neutron production and transport in the atmosphere. We compare the observed fast neutron flux with that calculated using the solar proton spectra reported at the times of the measurements; the causes for variation among the reported proton spectra and between the calculated and the observed fast neutron flux are discussed. The calculation reproduced the results of experiments by others with moderated slow neutron counters in and above the atmosphere. We calculate that the contribution of solar particle fluxes to the production rates of neutrons, to the production rates of radiocarbon, and to the leakage rates of neutrons from the top of the atmosphere are 2–3 orders of magnitude below the galactic cosmic ray contribution during solar cycle 20.

Alpha Particles in Solar Cosmic Rays over the Last 80,000 Years

Present-day (1967 to 1969) fluxes of alpha particles from solar cosmic rays, determined from satellite measurements, were used to calculate the production rates of cobalt-57, cobalt-58, and nickel-59 in lunar surface samples. Comparisons with the activities of nickel-59 (half-life, 8 x 10(4) years) measured in lunar samples indicate that the long-term and present-day fluxes of solar alpha particles are comparable within a factor of approximately 4.

О воздействии солнечных корпускулярных потоков на нижние слои земной атмосферы

О воздействии солнечных корпускулярных потоков на нижние слои земной атмосферы

A depth profile of 14C in the lunar rock 12 002

A depth profile of 14C in lunar rock 12 002 has been measured using six specimens with well-defined depth below the exposed surface of the rock. The results obtained show an excess surface activity attributed to solar particle flux.

A High-Resolution, Multiple Particle Spectrometer for the Measurement of Solar Particle Events

A particle spectrometer possessing high spectral and spatial/temporal resolution for the measurement of energetic protons, electrons and alpha particles over a broad energy and intensity range during solar particle events (SPE) was successfully launched aboard a polar-orbiting satellite on 17 October 1971. The spectrometer consists of a multi-element, silicon detector stack mounted within a plastic scintillator guard counter to form a particle telescope. The spectra of protons in the energy range 1.2-100 MeV, electrons from 0.88-1.6 MeV and alpha particles from 1.6-500 MeV are measured in four time-shared modes of operation with dual 256-channel pulse-height analyzers (PHA) of the successive-approximation type. Integral counting rates from each of the main elements of the telescope and the guard counter are measured every 32 milliseconds with low-power CMOS digital counters to provide high spatial/temporal resolution on the solar particle fluxes. Complete spectra on all three particle types over the above energy ranges are obtained every few seconds. A detailed description of the spectrometer, including a discussion of the mode logic which enhances the counting statistics in selected energy ranges, the dual pulse-height analyzers and the methods of obtaining the high temporal resolution is presented. Preliminary worldwide flight data obtained from two identical spectrometers oriented at different directions to the particle flux are also presented.

North-south asymmetry of solar-particle fluxes in polar-cap regions

On January 24, 1969, an experiment on the Esro 1/Aurorae satellite recorded a flux over the central north pole that at times was a factor of 7 greater than that seen over the south pole. This asymmetry is discussed in relation to the interplanetary-field direction measured at the same time by the Heos spacecraft, and comparison is made with the opposite asymmetrical configuration observed by Evans and Stone (1969) on November 2, 1967. From the evidence of two events it would appear that a southward interplanetary field plays a significant role in permitting direct access, while the magnitude and polarity of the asymmetry are determined by, respectively, interplanetary-particle anisotropy and the ‘toward’ or ‘away’ nature of the field.