摘要:

The intensity and energy spectrum of neutrons above 1 Mev produced in the solar photosphere by flare‐accelerated protons and α particles is calculated. The solar neutron yield from accelerated particles on helium is found to exceed the yield from evaporation and spallation in heavier elements for incident energies above about 30 Mev and continues to dominate until about 1 bev. At higher bombarding energies, thep, π+nreaction in hydrogen is the main neutron source. More than 90% of the total solar neutron production is from knock‐on reactions by protons in hydrogen and helium. Owing to this relatively high ratio of knock‐on to evaporation neutrons, the solar neutron spectrum is much higher in energy than the spectrum of secondary neutrons produced in the earth's atmosphere by galactic cosmic rays. A Monte Carlo calculation is performed to determine the solar neutron flux escaping into space. The absolute intensity of the solar neutron flux at the earth and its geophysical significance will be treated in the accompanying paper,

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04077

年代:1965

数据来源: WILEY

摘要:

The intensity and energy spectrum of solar neutrons at the earth relative to the flux of solar protons observed during the last solar cycle is calculated, using the solar neutron production spectrum obtained in the preceding paper, part 1. The time‐average solar neutron flux above 10 Mev at 1 AU over the last solar cycle is found to be 3×10−3neutron/cm2sec, with a peak intensity at 30 to 40 Mev. This solar neutron flux is comparable to the neutron leakage flux above 10 Mev produced by interactions of galactic cosmic rays with the earth's atmosphere, indicating that solar neutrons may be competitive with leakage neutrons as a source of high‐energy decay protons and electrons in the earth's radiation belts. Several anomalous features of the radiation belts are qualitatively consistent with a solar neutron source of the calculated intensity and spectral shape. Following individual major flares, essentially monochromatic bursts of solar neutrons should be observable at high altitudes and latitudes, but no sea‐level effects are expected. The search for solar neutrons should be pursued with a counter sensitive above 10 Mev, carried in a satellite in equatorial orbit during the first hour after a maj

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04087

年代:1965

数据来源: WILEY

摘要:

To get an empirical expression for σD/Do, the variation of the differential primary spectrum, the data of four neutron monitors (Ottawa, Mt. Washington, Climax, and Mt. Norikura) accumulated during most of the solar cycle are used in the expressionwhere (d/dP) (ΔI/Io) is the slope of the percentage variation‐rigidity curve, and (1/Io) (dIo/dP) is the neutron monitor response curve. The reference level is always June 1955. For statistical convenience, all data are smoothed by 12‐month moving averages and normalized to sea level. The rather small sensitivity of the neutron monitors below 4 bv rigidity and the lack of information for rigidities above 12 bv allow us to analyze only the interval between those rigidities. It is shown that no hysteresis is significant for the two principal periods of the solar cycle; June 1955 to February 1958 and March 1958 to March 1962 or 1963, according to the data available up to the moment of the analysis. The formula δD/Do= −0.036 (t‐ 5)4/3P−1.55for 4 ≤P≤ 12 bv is obtained for the decrease period, wheretis given in months from June 1955. The previous expression is valid for 5 ≤t≤ 32. Fort≤ 5, δD/Domust be zero in order to keep the constancy of the counting rate for almost the complete year of 1955. For the recovery period, δD/Do= −0.0083 (115 ‐t)4/3P−1.55is obtained for the same interval of rigidities. This expression is valid for 33 ≤t≤ 115. Here it is assumed that at the beginning of 1965 the solar cycle is recovered to the 1954–1955 level. The difference in the percentage variation of the counting rate for the Climax‐Mt. Norikura and Hermanus‐Buenos Aires pairs of stations is shown to agree with the calculated values obtained with the empirical laws. It is shown that the variational primary spectrums, obtained with the Japanese neutron monitor latitude surveys from the end of 1956 until April 1962, follow a power law with exponent near 1.6 for three cases and greater than 2 f

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04097

年代:1965

数据来源: WILEY

摘要:

Differential response curves and mean rigidity of response are computed for an ion chamber in free space using the cosmic‐ray spectrum at solar minimum and maximum observed by independent cosmic‐ray measurements. The response is found to be confined predominantly to the rigidity interval 1.5–2.5 bv during the entire solar cycle and is consistent with the observed modulation of He nuclei at these rigidities. The corresponding rigidity intervals for ion chambers flown on balloons at high latitudes and at Minneapolis are 2.5–3.5 bv and 3.0–4.0 bv, respectively. Using these results and the measurements made with ion chambers aboard the Pioneer 5 (1960), Mariner 2 (1962), and Ogo A (1964–1965) spacecrafts, ion chambers flown on balloons at high latitudes and at Minneapolis, and the He nuclei detectors, the rigidity dependence of the long‐term variation during 1960–1965 is found to be consistent with the formP−β, where β ≈ 0.8. For the subperiods 1960–1962 and 1962–1964, β is about

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04107

年代:1965

数据来源: WILEY

摘要:

Using sixth degree simulations of the quiescent geomagnetic field, we have studied the vertical cutoff rigidities of more than three hundred positions on the earth's surface. Twenty‐six of these positions are near the South African magnetic anomaly, and six other points are in a region of the North Atlantic where Pomerantz and Agarwal have reported anomalous results. The cutoff rigidities have been obtained by detailed computation of the trajectories of cosmic rays at 0.01‐bv rigidity intervals to allow for the effects of the penumbra. Differences greater than 15% from the Quenby and Wenk threshold values have been found in the vicinity of South Africa, the South Atlantic, and the Canary Islands. Various latitude surveys are shown to exhibit consistency when plotted against the cutoff rigidities determined by this computational method. It is concluded that, though there is essentially no difference between the cutoff rigidities obtained using two currently accepted field models, these simulations of the geomagnetic field are not completely adequate over some parts of the earth to describe the cosmic‐ray effects in their entirety. Cutoff rigidities for a number of neutron monitors are l

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04117

年代:1965

数据来源: WILEY

摘要:

A study of approximately 10 months of Explorer 14 observations of energetic electrons (E>1.6 Mev) in the outer radiation zone near the geomagnetic equator ∣λm∣1.6 Mev) intensities observed near the geomagnetic equatorial plane are consistent with the expected distortion of the geomagnet

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04131

年代:1965

数据来源: WILEY

摘要:

Using data from the satellite 1963 38C, we have measured the spatial characteristics of electrons trapped at highBvalues in the region 1.4 ≤L≤ 3.4. The data were obtained from an integral electron spectrometer sensitive to electrons of eneregyEe≥ 280 kev, ≥ 1.2 Mev, ≥ 2.4 Mev, and ≥ 3.6 Mev. An intense peak of electrons atEe≥ 280 kev and a corresponding lack of high energy (Ee≥ 1.2 Mev) electrons were observed atL∼ 2.5. Fluxes of 1.5(10)6electrons (Ee≥ 280 kev)/cm2sec ster were observed. A longitude dependence of the observed electron intensity was measured, and plots of the fractional electron transmission through the South Atlantic anomaly were obtained as a function ofBvalue on variousLshells. It was found that electrons mirroring atBvalues which remain above ∼350 km in altitude over the South Atlantic anomaly are not disturbed by the anomaly; about 90% of those that reach the 100‐ to 250‐km region over the anomaly are lost, and all those electrons reaching an altitude of ≤100 km over the anomaly are lost. The data indicate that particles are injected into the depleted regions at all longitudes, and that the resulting longitudinal intensity distribution is quite stable during magnetically quiet periods. The data further suggest that the loss of electrons in the anomaly and their subsequent replenishment is a general effect, occurring thro

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04139

年代:1965

数据来源: WILEY

摘要:

The motions of the magnetic field lines and of the plasma in the outermost region of the magnetosphere that are caused by a sudden change in the solar wind pressure are studied. Using Mead's model for the initial and the final field configurations of the magnetic field in the magnetosphere, the field line displacements due to a sudden solar wind pressure change are numerically computed. It is shown that the displacements for high latitude field lines have an appreciable azimuthal component. Thus a solar wind pressure change normal to the magnetospheric boundary surface is partially converted into tangential motions of the plasma inside the boundary, the momentum transfer being accomplished via the magnetic field. The mechanism can be described as a toothpaste‐tube effect. The polarization in the magnetic field perturbation expected from this process qualitatively agrees with that observed in sudden commencements. It is suggested that the rise time of a sudden commencement is determined mainly by the time required for the outermost region of the magnetosphere to reach the final equilibrium state. If the field lines in this region are assumed to move with the local Alfvén velocity, the observed rise times of sudden commencements can be explained. According to the above view, the rise time is expected to be the same everywhere in the magnetosphere; this is in agreement with the observations of sudden impulses made by Explorer

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04151

年代:1965

数据来源: WILEY

摘要:

The relationship between the solar wind velocity and the surface magnetic disturbance index is examined at high levels of disturbance through the use of sudden commencement data. It is shown that the results are not in agreement with an extension of those for low values of disturbance from Mariner 2, unless account is taken of the standoff distance between the flare plasma and the shock it causes. This correction will only be large enough to bring about agreement if the front of the plasma cloud is very broad.

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04159

年代:1965

数据来源: WILEY

摘要:

The interaction of a uniform plasma stream in the joint interplanetary and geomagnetic field when there is a magnetic field along the stream lines is considered. The discussion is restricted to two dimensions. It is assumed that in front of the stream and outside the geomagnetic field boundary a shock wave develops as in the case of supersonic flow past blunt‐nosed bodies. The magnetic field is found to be proportional to the particle flux density. The magnetohydrodynamic equations in the transition layer between the shock and the body are solved numerically, and the effect of the magnetic field on the stand‐off distance of the shock is considered. The body causing the assumed shock is obtained and related to the equatorial cross section of the geomagnetic field bound

ISSN:0148-0227    

DOI:10.1029/JZ070i017p04165

年代:1965

数据来源: WILEY