Large and abrupt magnetic field variations (|ΔB_y|>50nT within 1/16sec) observed over the polar ionosphere by the MAGSAT are analyzed statistically. More than ten-thousands of such events were found during the MAGSAT periods. The results suggest that they are the spatial variation of the magnetic field generated by the quasistatic field-aligned sheet currents, the width of it is less than 1km and such abrupt variations should correspond to very high density field-aligned currents (>90μA/m²). They are more frequently observed near the polar cusp region or dawn-side auroral oval than in other portions of the oval. The geomagnetic activity and the ionospheric conductivity strongly control the occurrence frequency.

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Studies of the relationships between auroral and concurrent geomagnetic pulsations, PiC, in the auroral zone are reviewed concentrating to the most recent developments. The processes are described which lead to a decisive conclusion that the magnetic pulsations are caused by temporal and spatial fluctuations of electric currents induced in enhancements of the ionospheric electric conductivity produced by pulsating precipitation of auroral electrons. The conclusion is further reached that the currents also account for magnetic fluctuations measured by MAGSAT above a pulsating aurora as well as PiC pulsations observed on the ground at the same time. The relationships between auroral and concurrent magnetic pulsations have now been firmly established, not only for the magnetic pulsations on the ground, but also for those observed by a low altitude satellite above the ionosphere.

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Since the advent of digitally recording magnetic variometers and the ready accessibility of computers, there has been a search for a technique to produce K-indices of geomagnetic activity by machine.
The principal difficulty in the determination of K-indices is the estimation of the regular solar diurnal variation (SR) for each day, which is used as a reference from which the K-Variations are scaled. A number of methods for the machine estimation of the daily SR are reviewed. These fall into two categories: (i) by use of neighbouring quiet days, or (ii) filtering out the high frequency harmonics. Of the techniques proposed to date, those which are data adaptive are considered preferable.
A data adaptive method which divides a magnetogram trace into high and low frequency harmonics is presented. It is found that there is no particular frequency below which can be considered all the SR variations and above which are all the K-variations.
The latitude dependence of the tolerace to differences between estimation of the SR by machine and that manually is also discussed.

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Whether the ratios H_z/H_y^(t), H_z/H_y^(a) are independent of the electromagnetic inducing period is a crucial property for studying two-dimensional induction anomalies. We have recalculated the two ratios over a range of period for a half-cylinder anomaly model (suggested by Summers) using both the integral equation method and the finite difference method. We have obtained results which are significantly different from Summers'. In particular, we find that H_z/H_y^(t) is frequency dependent, implying that if we observe that H_z/H_y^(t) is frequency independent, we may not use the local induction model to interpret the result. Besides, a reexamination of the situation is presented.

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The screening of domain moments associated with the displacement and pinning of a single domain wall from an initial energy minimum position is investigated. The domain moment acquired by the pinning of a domain wall in this fashion is reduced (or screened) by the subsequent readjustment of the non-pinned, mobile domain walls within the magnetic material. Although only a simple, one-dimensional domain geometry is considered, the screening effects are quite variable depending on the grain size, the number of domains and which wall is pinned. In all cases, however, the screening in grains with a few mobile domain walls is generally very large. The results of these screening calculations have important consequences regarding the grain size dividing stable from unstable remanence in multidomain grains.

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The new technique of spherical cap harmonic analysis has enabled a model to be constructed of both the main geomagnetic field and its secular variation, that applies to Canada and its adjacent areas over a time range of 25 years. The technique permits the optimum utilization of data over only a portion of the earth's surface, while ensuring that the curl and divergence of the total magnetic field vector are identically zero. With this technique, proper consideration can be taken of altitude variation, a particularly important factor when dealing with satellite data. The effect of crustal anomalies on the determination of the secular variation (SV) model was eliminated by fitting SV independently of main field, and then integrating the SV model. Main field data at epoch 1985.0 were derived by updating Canadian aeromagnetic and Magsat satellite data by means of that integrated SV model. A spherical cap harmonic residual model was constructed from the updated main field data after subtraction of the 1980 International Geomagnetic Reference Field (IGRF 1980) extrapolated to 1985.0. Merging this residual model for 1985.0 and the integrated SV model provided a model with maximum spatial index of 16 for the main field terms at epoch (temporal degree 0) and of 4 for the integrated secular variation terms (temporal degrees 1 to 3), over a spherical cap of half angle 30°. The vector sum of the residual model and the IGRF 1980 at 1985.0 is called the Canadian Geomagnetic Reference Field 1985, and applies from 1960 to 1985 with extrapolation possible to 1990. This reference field has been used to produce the Magnetic Charts of Canada for epoch 1985.0.

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An unusual archeological example of multiple heating leading to superimposed thermoremanent magnetizations (TRM's) is described. The samples involved are roof-tiles which have been incorporated into the floor of a 6th century A. D. kitchen oven at a site near Potenza in southern Italy. Up to 300°C, thermal demagnetization reveals a pattern of diverging great circles which is interpreted as a “cooking” overprint; 100-300°C vector differences yield D=000°, I=+55°, k=81. Above 500°C stable “end-points” are obtained and a statistical argument strongly suggests that these represent a TRM acquired when the tiles were originally kiln-fired. A third, intermediate-temperature, component is present, but its origin is unclear. It cannot be an unresolved mixture of the other two, and it is not spatially organized in any obvious manner—we suggest that it was acquired when the tiles were involved in a fire. Thus it appears that quite complicated magnetic histories can be recorded by, and recovered from, archeological materials.

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