摘要:

Many observations show that low rigidity protons from solar flares are permitted entry at Minneapolis only during the main phase of magnetic storms. The measured energy is much below the normal Störmer cutoff at that time. This paper develops the idea that a ring current responsible for the main storm field reduces the Störmer cosmic‐ray cutoffs. The model of the ring chosen is actually an azimuthal current on the surface of a sphere with current intensity proportional to sin θ where θ = colatitude. It is shown that this mathematical form permits great simplicity in the analysis and leads to essentially the same result as a diffuse ring corresponding to the actual trapped radiation. The magnetic moment of the ring required to produce the cutoff change can be provided by reasonable intensities of very low energy trapped radiation. It is shown that the cosmic‐ray data permit one to evaluate both the moment (M′) and radius (R) of the ring, whereas the surface magnetic measurements determine only the quantityM′/R3. Since observation shows that the cosmic‐ray cutoffs return to normal during the main phase, it must be assumed that the ring shrinks inward so that the surface field is maintained negative. Cosmic‐ray evidence concerning the presence of a permanent ring current is discussed. Such a ring is measured directly by satellites dur

ISSN:0148-0227    

DOI:10.1029/JZ066i012p03991

年代:1961

数据来源: WILEY

摘要:

This paper shows that any particles affected by the Capetown magnetic anomaly do not have trajectories that would pass through the position of the experimentally observed minimum in the outer belt. Therefore, the minimum cannot be taken as evidence either for the effect of the anomaly on the trapped radiation or for support of the neutron albedo source for the outer zone electrons.

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04003

年代:1961

数据来源: WILEY

摘要:

During the International Geophysical Year, two series of balloon flights were made. One of these sampled the ionization due to cosmic rays over the range of geomagnetic latitudes from 38°N to 87°N. The other covered the range from 13°N to 79°S. In each case similar balloon flights from a base station were made to make possible an allowance for changes in the primary radiation. The second series of nights is used in this paper to determine the location of the knee of the latitude curve at atmospheric depths from 10 to 220 g cm−2. The results indicate that at this time of the solar cycle the knee moved toward the pole with decreasing amount of air overhead, reaching a geomagnetic latitude of 55° at 10 g cm−2. This movement of the knee becomes very slow at the lower pressures, however, suggesting that even at much lower pressures, the knee would not move appreciably farther toward

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04007

年代:1961

数据来源: WILEY

摘要:

The magnetic field of a model ring‐current belt encircling the earth symmetrically is numerically calculated, to a first approximation, for a particular model belt already discussed byAkasofu and Chapman[1961a]. They calculated the first approximation to the field only for points in the equatorial plane. The whole distribution of the field is here discussed, and for a particular intensity of the belt the calculation is carried to a second approximation. It is shown that over the earth's surface the field of the ring current is nearly uniform, though in auroral latitudes the diamagnetism of the belt produces an insignificant irregularity in the field disturbance. The model belt considered here is one whose center line is connected with the auroral zone by the dipole field lines of force; its particles have not yet been observed directly. Its existence is suggested by the quiet‐day anomaly of the satellite‐observed magnetic field at that distance. The known Van Allen radiation belts seem likely to contribute little to the ring current field, but during magnetic storms the radius of the belt mainly responsible for this field is probably less than 6 earth

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04013

年代:1961

数据来源: WILEY

摘要:

The ability of the cosmic‐ray neutron albedo mechanism to account for geomagnetically trapped electrons is investigated quantitatively. Injection as a function of energy, pitch angle, and altitude is computed from a reasonable neutron albedo model. Loss mechanisms (slowing down and pitch‐angle diffusion) based on Coulomb interactions with the residual atmosphere are considered to act both independently and simultaneously. It is found that slowing down is generally dominant. The resulting electron belt has the following features: (a) an intensity whose energy spectrum shows a peak at ∼200 kev; (b) an angular distribution that is approximately ‘isotropic’ up to the loss cone; and (c) an omnidirectional, integral intensity in the geomagnetic equatorial plane that is approximately constant vs. altitude. The absolute intensities depend directly on the atmospheric model used in the calculation; namely,rv−2.7, where atmospheric density is taken as ρ0r−v. These results agree only poorly with spectrometer observations which show an energy spectrum with a peak at a much lower energy. However, the quantitative agreement as to intensity is good at energies ≳400 kev. It is concluded that only a small fraction of the trapped electrons can be accounted for in terms of neutron albedo, essentially all trapped electrons>400 kev. An ‘auroral’ component of low‐energy electrons is also present. The energy of this low‐energy component probably derives from local acceleration, and ultimately from the sun. The effect of the Capetown magnetic anomaly is investigated and shown to produce a ‘slot’ of only 2 per cent in the equatorial plane in the

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04027

年代:1961

数据来源: WILEY

摘要:

The trajectories of charged particles moving in a magnetic dipole field have been calculated by numerical integration for application to data on the intensity variation of cosmic rays during recent solar events. All seasons and times of day have been covered by assuming a range of orientations of the incident particle beam with respect to the magnetic dipole axis. The points of impact with the earth have been determined for protons with energies from 0.05 to 50 bev. The computation includes 4000 trajectories and fills several gaps in previous investigations. In agreement with earlier calculations the results indicate that the protons strike in well‐defined areas between O and 1200 hours local time, and are focused into small areas of impact at low energies. The investigation has revealed two points that are not new but have received relatively little attention in earlier work. First, the relative number of impacts in the northern and southern geomagnetic hemispheres is strongly dependent on season. Second, under certain conditions of season there is a class of trajectories, which may be called quasi‐trapped, constituting a set of paths resembling the trapped trajectories first discovered by Störmer but connected to infinity. It is suggested that injection into trapped orbits from these quasi‐trapped trajectories may make a contribution to the population of the Van Allen

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04047

年代:1961

数据来源: WILEY

摘要:

Polar‐cap absorption of radio waves has been shown to be caused by an influx of fast particles emitted by the sun at the time of certain solar flares. The steady‐state daytime and nighttime electron‐density profiles produced in the lower ionosphere by such a particle flux are calculated, on the assumptions that the particles are protons and that their differential energy spectrum is of the formn(E) dE = KE−5dE, with a sharp cutoff at the low‐energy end. The shapes of the profiles are shown to be almost independent of the proton spectrum and low‐energy cutoff, provided the latter is higher than about 10 Mev. The radio‐wave absorption this ionization would produce is calculated for frequencies of 30 Mc/s and 60 Mc/s. Conditions during the twilight transition period are also examined, assuming that O2−is the only negative ion present. The photodetachment coeflicent of O2−is calculated as a function of solar zenith angle, and corresponding electron‐density profiles deduced. By comparing the absorption these profiles would produce with the observed variation of cosmic noise absorption during twilight, it is shown that the presence of O2−alone is insufficient to account

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04071

年代:1961

数据来源: WILEY

摘要:

Damped waves of a period of several minutes with amplitude up to several hundred gammas are found in the geomagnetic field in the auroral zones. These damped waves occur simultaneously in magnetically conjugate regions in the northern and southern hemispheres. The waves are very nearly elliptically polarized in the plane approximately perpendicular to the magnetic field. Hence the damped waves are interpreted as low‐frequency hydromagnetic waves generated in the exosphere at an altitude of several earth radii and transmitted to the earth along the lines of magnetic force in the longitudinal mode of propagation. The number of occurrences of these damped waves has a distinct local time variation that appears to vary with seaso

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04087

年代:1961

数据来源: WILEY

摘要:

Sudden commencements of magnetic storms observed during the IGY are analyzed using the rapid‐run magnetograms taken at College, Sitka, Fredericksburg, Honolulu, Watheroo, and Marie Byrd. Most of the magnetic impulses of sudden commencements are found to be elliptically polarized at all these stations except at Honolulu; at this latter (low‐latitude) station the polarization is usually linear. The following model is presented for sudden commencements. The impact of the solar gas stream upon the geomagnetic field creates a shock wave, which propagates to the earth as a longitudinal hydromagnetic wave in low latitudes. The compressional wave in the shock generates transverse hydromagnetic waves that propagate to high latitudes along the magnetic field lines. Since the field lines are firmly anchored in the conducting core of the earth, a strong shock may cause the field lines to oscillate for a considerable length of time. These oscillations are, in fact, observed in high latitudes as continuous waves following the sudden commencement. The frequent appearance of a reversed impulse, preceding the main impulse at geomagnetic latitudes above 40°, is due to the circumstance that at the time of the arrival of the transverse wave at the ionosphere the direction of the magnetic perturbation vector is south of the geomagnetic east‐west, and that the vector subsequently rotates toward the north. Thus physically there is no essential difference between sudden commencements with a reversed impulse and those without it. The peculiar shape of sudden commencements inHobserved during morning hours in latitudes above 50° can also be explained by a particular phase of the elliptically polarized wave at the time of arrival in these regions and the subsequent rotation of the magnetic vector. The picture of sudden commencements is thus greatly sim

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04097

年代:1961

数据来源: WILEY

摘要:

Artificial satellites orbiting in the ionosphere normally tend to acquire a slight negative charge due to the high velocity of the electrons relative to the ion and satellite velocities. (At very high altitudes where the ionospheric electron concentrations are small, and in the presence of solar radiation, satellites tend to have a small positive charge due to the photo‐electric effect, which in this case predominates over the ionospheric effect.) If the attempt is made to change the potential of a satellite by ejecting energetic beams of electrons or positive ions, the ionosphere provides some rather stringent limitations on the potential that can be achieved, for a substantial potential on a satellite causes appreciable currents to flow between the satellite and the ionosphere, which is a highly conducting medium containing a large reservoir of charge. The physics of the ionospheric limitation on satellite charge is investigated, and it is shown how the satellite charge and potential depend on injection currents and ambient charge density for both intermittent and continuous injection current

ISSN:0148-0227    

DOI:10.1029/JZ066i012p04113

年代:1961

数据来源: WILEY