Twenty-three geomagnetic storm events during 1966-70 have been studied by using simultaneous interplanetary magnetic field and plasma parameters. Explorer 33 and 35 field and plasma data have been analyzed on large-scale (hourly) and small-scale (3min) during the time interval coincident with the initial phase of the geomagnetic storms. The solar-ecliptic B_z component turns southward at the end of the initial phase, thus triggering the main phase decrease in D_st geomagnetic field. When the B_z is already negative, its value continues to remain negative. The B_y component also shows large fluctuations along with B_z. On the small-scale behavior of the magnetic field and electric field (E=-V×B) studied in details for the three events, it is found that the field fluctuations in B_y, B_z and E_y and E_z are present in the initial phase. These fluctuations associated with the passage of the shock waves, continue to exist during the initial phase. In the large-scale behavior field remains quiet because the small-scale variations are averaged out. The power spectrum analysis for few events using 5.11 sec data shows the steepening of the spectrum after the passage of the shock wave associated with the ssc. It appears that large as well as small time-scale fluctuations in the interplanetary field and plasma may play a role in altering the internal electromagnetic state of the magnetosphere so that a ring current could start causing a geomagnetic storm decrease.

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The response of the ionosphere in an altitudinal range of 50-200km to the great solar flare that occurred at about 1500UT on 7 August 1972 is studied. Sudden increases in electron concentration, Pedersen and Hall electric conductivities (SIEC), total electron content (SITEC) and sudden cosmic noise absorption (SCNA) due to solar X-ray flux increments at 1530, 1600, 1700 and 2100UT are calculated for the location of 40°N latitude and 75°W longitude, and some of the results are compared with observed values. The solar X-ray emissions concerned in this study are those with wavelengths of 1-100Å, of which emission fluxes measured from the SOLRAD 10 satellite are available for the 1-20Å band, while emission spectra for other wavelength bands are assumed. Two altitudinal profiles of increased electron concentrations at each time are first derived based on two assumed effective recombination coefficient profiles, then associated increments in 30MHz cosmic noise absorption and Pedersen and Hall electric conductivities are derived. It is found that the calculated 30MHz SCNA's (SCNA values) and SITEC's (50-200km) at 1530, 1600 and 1700UT for one of the increased electron concentration profiles are in reasonably good agreement with the observed ones, but the SITEC's roughly corrected for the entire ionosphere at 1530 and 1600UT seem to be greater by more than 20 and 30% than the observed ones, respectively. These results seem to imply that the derived electron concentration enhancements in the ionosphere above about 100km are overestimated.

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Monthly and semimonthly harmonic analyses of H are performed and some evidence of a diurnal variation of the lunar tide strength is found. Contamination of the data by magnetic disturbance can be identified by examining the phase progression in local time of the semimonthly component. This contamination is also found in the work of some other authors. It is suggested that some effects previously described as “lunar” are due to other causes.

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The paper describes a data conversion and editing system devised to handle large amounts of data produced on film by recording magnetometers used in array studies. The field data are in the form of five analog traces on 35mm photographic film. The film is scanned by a fine light spot obtained from a flying spot scanner cathode ray tube. The spot position and intensity are controlled and corrected by dedicated electronic hardware. The intensity of the light transmitted through the film is measured and converted to digital form suitable for recording in I. B. M. compatible magnetic tape format. At this point the data may be recorded on an incremental tape transport, without further modification, to form a minimum cost system. Our system was expanded to use part of the time available on a local PDP-11 computer, which was already controlling a continuous data link to the University of Alberta Geophysical Observatory. The optical scanning is controlled asynchronously as the lowest priority task. A first level editing procedure uses centroid calculation and noise rejection to reduce by a factor of about 13 the number of data points recorded. The reduced and buffered data records are written synchronously in I. B. M. compatible form on magnetic tape. The final editing, including the sorting of crossed traces, is done at the I. B. M. 360-67 installation by direct operator interaction via a graphic terminal and lightpen. While the system was devised for the specific magnetometer array task the basic hardware could be used quite generally for reliable and economic conversion of analog traces on 35mm film to a computer compatible digital form. The low-cost practical limitations produce a system with a definition of -10⁶ points/square frame with a 64 gray level acceptance scale for the transmitted light.

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To evaluate two candidate models proposed for the IGRF secular change 1975.0 (BARRACLOUGH et al., 1975; FABIANO and PEDDIE, 1975), a conference was held at the Geographical Survey Institute in Tokyo on July 21, 1975. This is a summarized report of the conference.
The geomagnetic field and its secular change were computed based on the proposed models and compared with the observed data in Japan and its surrounding areas. Two kinds of comparison were made. One is a comparison of the computed secular changes with continuous field variations obtained at fixed sites for the past several years. The other is a comparison of spatial distributions of the rate of change in the field at a particular epoch.

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