Low Geomagnetic Latitudes Research Articles

MAGNETIC AND TELLURIC CURRENT DISTURBANCES IN ALASKA

Much of Alaska lies in or near the auroral zone, where magnetic and telluric current disturbances are large compared to those at lower geomagnetic latitudes. Pronounced and different diurnal variations of disturbance are evident from analysis of K indices from Barrow, College, and Sitka magnetic observatories. The quietest period for magnetic or electrical surveying is the late morning and afternoon hours locally. Recordings of telluric current disturbances can be used as a sensitive indicator of ionospheric activity. The large amplitude and rich frequency spectrum of the telluric currents suggests their use as a prospecting tool in Alaska.

Energy Dependence of Transient Changes in the Primary Cosmic-Ray Spectrum

Quantitative comparisons are made between the cosmic-ray intensity variations observed by a Geiger counter telescope and ionization chamber at a high geomagnetic latitude, high latitude neutron monitors at sea level, and at two different mountain altitudes, Geiger counter telescopes situated 40 meters of water equivalent underground, and a neutron monitor and Geiger counter telescopes at a low geomagnetic latitude. Long-term and short-term variations are considered. As the intensity variations were large, and as the instruments were all of good statistical accuracy, considerable reliance can be placed in the determinations. It is shown that similar comparisons published by other investigators are in agreement with these determinations, provided adequate allowance is made for the altitudes at which the data were obtained. Writing the differential energy spectrum of the primary cosmic radiation as $j(E)$, and measuring $E$ in Bev, the inter-instrument comparisons are used to show that the average spectral changes approximate to the law $\ensuremath{\delta}j(E)=\mathrm{const}{(1+E)}^{\ensuremath{-}\ensuremath{\beta}}j(E)$; where $\ensuremath{\beta}\ensuremath{\approx}0.9$ for short-term variations, and $\ensuremath{\beta}\ensuremath{\approx}1.2$ for long-term variations.It is shown that the amplitude of the long-term variation is markedly dependent upon altitude. Some evidence is presented that there might be a north-south asymmetry in the long-term variation, the amplitude being greater in southerly directions.

The Effect of Proton Gyration in the Outer Atmosphere Represented on the Dispersion Curve of Whistler

A short whistler observed at Kyoto was analyzed to detect the effect of proton gyration on the whistler dispersion. The parabelic distribution of electron density in the ionosphere was adopted. The propagation path of the whistler was divided into two parts with respect to altitude, and the electron density was constant in each part. Results indicated that the dispersion of whistlers observed at low geomagnetic latitude is clearly influenced by the effect of proton gyration in the outer atmosphere. (M.C.G.)

Auroral ionization and the absorption and scintillation of radio stars

The absorption of the radiation from extra-terrestrial radio sources, when observed at low elevations to the north of Jodrell Bank (Geomagnetic latitude 56°), is discussed. At lower culmination the Cygnus radio source is at an elevation of only 4°, and the line of sight to the source then passes through the ionosphere near the zone of maximum auroral activity. Combined observations of the source intensity at 36 Mc/s and 100 Mc/s, and of radar back-scatter echoes at 36 Mc/s, have been made using the 250 ft steerable telescope. The absorption and certain back-scatter echoes can be related to an ionized layer at a height of the order of 100 km, associated with auroral activity. It is shown that with a high sensitivity radar equipment at 36 Mc/s, weak auroral-type echoes from irregularities in the E-region aligned along the earth's field occur on about 40 per cent of all days at quite low geomagnetic latitudes. The suggestion is made that the scintillation of radio stars observed from latitudes similar to that of Jodrell Bank is not due entirely to irregularities in the F-region, but that there is a large contribution from these aligned irregularities at E-region heights.

Triple-splitting of the F-echoes

An account is given of the polarization studies made on the triple F-echoes, obtained by employing pulses of waves of frequency, 3 Mc/s, at vertical incidence. The polarization studies revealed that the first component after the ground-pulse was the normal extraordinary component having a right-handed sense of rotation, the second component was the normal ordinary component having a left-handed sense of rotation and the third component was the Z-component having a left-handed sense of rotation. In addition to the coupling process suggested by Eckersley and Rydbeck between the ordinary and extraordinary waves, and operative only in high geomagnetic latitudes, the partial reflection and transmission at the level of ionospheric reflection for the ordinary component have been considered as a plausible process for getting the Z-component. Since the coupling process is not likely to produce a detectable Z-component at low geomagnetic latitudes, the occasional presence of the Z-component at low latitudes has been attributed to the partial reflection and transmission process which may take place at all latitudes. The view that the Z-component really corresponds to the left-handed ordinary component suffering reflection at the level corresponding to p 0 2 = p 2 + p · p H has been supported.

Abnormal Ionization in the Lower Ionosphere Associated with Cosmic-Ray Flux Enhancements

Abnormal ionization in the lower ionosphere associated with cosmic-ray flux enhancements is discussed mostly in terms of the great solar event of February 23, 1956. Two kinds of abnormality were recognized: early effects observable in the dark hemisphere at the time of the sudden cosmic-ray enhancement, and late effects which began gradually and reached a maximum a few hours after the cosmic-ray enhancement. The late effects died away over a period of several days in geomagnetic latitudes above 70°, but more rapidly in lower latitudes. Both effects were more intense in higher geomagnetic latitudes. Early effects, though much the less intense of the two, appear to have been observable in lower geomagnetic latitudes than the late effects. The early effects are explained as a consequence of a plausible difference in composition between streams of solar particles of cosmicray energies, and ordinary cosmic rays. The late effects are explained in terms of ionization produced in the lower ionosphere (the range of height from 30 to 110 km is studied) by the passage or stopping of solar particles-mostly protons. Such particles are shown, like the more energetic solar cosmic rays, to be arriving essentially isotropically after the maximum effects occur. A plausible extension of the observed magnetic-rigidity spectrum of the solar cosmic rays downward in rigidity by about a power of 10 would provide the protons necessary to account for the observations. The absence of auroral and significant magnetic activity accompanying the abnormal ionization is consistent with the explanations offered.

Radio echoes from auroral ionization detected at relatively low geomagnetic latitudes

High-frequency radio echoes from ionization associated with the Aurora Borealis have been identified at Stanford University (geomagnetic latitude <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43.75\deg</tex> ). The echoes occur at ranges between 1400 km and 4700 km corresponding to reflection from ionization in the zone of maximum auroral occurrence located far to the north of Stanford. The formation of the ionization is attributed to the bombardment of the upper atmosphere by high-speed charged particles emitted from the sun. The echoes have great amplitudes with duration times between one second and one hour. Their appearance and disappearance is quite similar to the behavior of visual auroras; the occurrence of the echoes has been found to be related to geomagnetic disturbances. The heights of reflection appear to be between 100 km and 1200 km above the surface of the earth. The paths which the auroral signals travel over the relatively enormous distance from Stanford to the auroral zone (and back) are greatly influenced by the presence of the normal ionospheric layers. The echoes have been observed at ranges and bearings which indicate reflection from ionization at points along the auroral zone all the way from eastern Canada to Alaska.

Magneto-Ionic Triple Splitting Over Delhi

AbstractThe paper presents some observations of the rare occurrence of triple magneto-ionic splitting over Delhi. The various possible causes for the occurrence of this phenomenon at the low geomagnetic latitude of Delhi have been discussed. It has been indicated that the triple splitting is likely to be caused by the longitudinal propagation of the ordinary ray associated with an increase in the collisional frequency of the ionospheric layers.

Fine structure in the directional intensity of cosmic rays at Hyderabad

Fine structure measurements are taken at Hyderabad (λ=7·7° N) in both the east and west azimuths. Two triple coincidence telescopes making angles of 9° 38′ and 5° 18′ in the zenith, in the eastern azimuth and western azimuth respectively are employed. The observations are taken in steps of 5° from the vertical upto 45°. The results show the existence of fine structure for the first time at such a low geomagnetic latitude as 7·7° N.

Changes in Cosmic Ray Intensity Associated with Magnetic Storms

IT is usually supposed that the world-wide changes in cosmic ray intensity associated with a magnetic storm are due to variations in the earth's magnetic field produced during the storm. This seems to be excluded, however, by recent observations by Lange and Forbush1, who have found that the intensity varies (decreases and increases) even at Godhavn, which is situated at so high a geomagnetic latitude (80°) that the earth's magnetic field cannot possibly affect the intensity. Further, the variations cannot be due to changes in the solar magnetic field, because they are observed even at Huancayo, which has a low geomagnetic latitude (0.6°) so that it is reached only by the high-energy particles which are certainly not influenced by the solar magnetic field. Then the only possible explanation seems to be that the variations in cosmic radiation are due to changes in the earth's electrostatic potential.