The solar cycle line has been resolved in the horizontal force by power spectrum analysis using 120 years' data of Colaba-Alibag. Having established the presence of a large signal, the variation and phase in relation to solar cycle have been computed from the data of eight observatories by the application of an appropriately designed band-pass numerical filter. The response in the horizontal force has been found to be larger and more uniform than estimated earilier. At most of the stations, the response was still greater during peaks of odd solar cycles suggesting a 22-year variation in the field. An unexpected 17 to 18 year cyclic variation has also been noticed in the autocorrelation function of the data series of Colaba-Alibag. The data of this station, after removal of the secular variation, also suggest the presence of an 80 year cycle in the horizontal force.

View full abstract

The departure from the perfectly geometrical shape of the conducting body substantially changes its electromagnetic response. The interpretations regarding the dispositions of the body assuming an underformed shape have to be suitably modified if it is in reality deformed.The quantitative contribution of small deformation has been obtained using a perturbation technique. Both global and small-scale conducting structures, employing spherical and cylindrical models respectively, have been considered. Numerical computations have been made to find the depth estimate of the first major conductivity discontinuity in the Earth, when its boundary is assumed to be perturbed. The results have application in the interpretation of anomalies in the geomagnetic variations.

View full abstract

Experimental studies on PRM (Kinoshita 1968) are discussed theoretically on the basis of a multiaxial single domain model developed in a previous paper (Nagata and Kinoshita, 1965) in which irreversible rotation of the spontaneous magnetization vector I_s of individual ferromagnetic fine grains of the specimen at a certain value of external compressional stress is taken into account to explain the acquisition of PRM.
It is assumed that the external stress exerted on a specimen is a purely uniaxial compressional stress whose intensity varies from grain to grain, in the from of Gaussian distribution. PRM versus pressure and PRM versus external magnetic field relations are qualitatively well explained by the single domain model.

View full abstract

Various characteristics of piezo-remanent magnetization of igneous rocks are experimentally demonstrated in small magnetic fields, H=0-10Oe., and under uniaxial compression comparable to the earth's crust stress, 0-100kg/cm². The main characteristics observed are as follows:
(a) “After-effect” of uniaxial compression: J_R(P₊P₀H₊H₀).
After a rock sample is uniaxially compressed in a non-magnetic space by a pressure P larger than a certain critical value (P_c), its IRM, J_R(P₊P₀H₊H₀), becomes larger than the ordinary IRM, J_R(H₊H₀), without such a pressure treatment. This after-effect of pressure takes place in both cases of P//H and P⊥H.
Here [d/dPJ_R(P₊P₀H₊H₀)]_H=const>0 for P>P_c.
(b) “Pressure demagnetization” effect: J_R(H₊H₀P₊P₀).
After uniaxially compressing a rock sample having IRM, J_R(H₊H₀), in a non-magnetic space, the residual magnetization, J_R(H₊H₀P₊P₀), becomes appreciably smaller than the original intensity of J_R(H₊H₀) in both cases of P//H and P⊥H.
Here [d/dPJ_R(H₊H₀P₊P₀)]_H=const<0, and [d²/dP²J_R(H₊H₀P₊P₀)]_H=const>0.
(c) “Non-commutativity” of P and H.
An inequality relationship expressed as
J_R(H₊P₊P₀H₀)≥J_R(P₊H₊P₀H₀)>J_R(H₊P₊H₀P₀)≥J_R(P₊H₊H₀P₀)
holds for all samples. In a magnetic field larger than a certain critical value, H*,
J_R(P₊H₊H₀P₀)<J_R(H₊H₀), but in H<H* J_R(P₊H₊H₀P₀)>J_R(H₊H₀).
J_R(H₊P₊P₀H₀) and J_R(P₊H₊P₀H₀) are always larger than J_R(H+H₀). The above argument holds in both cases of P//H and P⊥H.
(d) A linear dependence of PRM on H.
J_R(H₊P₊P₀H₀) is defined as piezo-remanent magnetization. In a range of small magnetic fields,
J_R(H₊P₊P₀H₀)∞H for P=constant, though J_R(H₊H₀)∞H² in the

View full abstract

Electric vertical and horizontal NS and EW components of natural ELF electromagnetic noises were observed through a year from February, 1967, to January, 1968. Mean diurnal variations of the Schumann resonance power were obtained for the first three modes from noise spectra. The variations show completely different patterns for each component, and change considerably month by month. The diurnal amplitude also varies by 1 to 7db from the mean daily values. The results are compared with the diurnal variations derived from the simple theory considering worldwide thunderstorm activity as noise sources. There are fairly good agreements between the experimental and theoretical results, especially for EW component. For vertical and NS components thunderstorm effect from Africa seems relatively smaller then expected. The time of this effect is in local night. This shows that local night conditions of the lower ionosphere as the upper boundary of the earth-ionosphere cavity, make the received intensity of vertical and NS components decrease.

View full abstract

The global atmospheric electric current flow may be determined, if local influences can be eliminated, by measuring the total Maxwell current flowing to the surface of all fairweather areas. A new method to reduce the effect of locally produced disturbances on surface measurements of the atmospheric electric current density is described. Experiments indicate that in the time domain from a few seconds to a few hours the standard deviation of the total current density decreases approximately with the square root of the sensor size. Locally generated currents may therefore be effectively suppressed by area averaging.

View full abstract

Solar proton flares take place due to the release of magnetic energy accumulated within the sunspot magnetic flux tube of force lying in the chromosphere and the lower corona due to the twisting of it, which is seen from the rotational motion of sunspot groups on the photospheric surface. This rotational motion is counterclockwise (clockwise) in the northern (southern) hemisphere when viewed from the earth. The accumulation of magnetic energy within the flux tube due to this motion continues to proceed until some instability is induced along the flux tube. It is further shown that the magnetic configuration of sunspot groups is important for the triggering of a solar proton flare.

View full abstract