[en] A study is made of the role which a positive (northward) component of the interplanetary magnetic field (IMF) Bsub(z) may play in triggering large magnetic storms. The study is made over a 15 year period (1964-1978) by selecting storms with Ksub(p) >= 7₀ and which are preceded by a Sudden Commencement (Ssc). The correlation between the geomagnetic index Ksub(m) and the three-hourly averaged Bsub(z) is established both on a statistical basis and on a case-by-case study. Storms associated with Bsub(z) > 0 are found to be less intense than those associated with Bsub(z) < 0, but major storms can be also triggered by solar wind events associated with a northward IMF. The relation-ship between interplanetary electric field Esub(γ) and Ksub(m) is also given. By using this relation together with the one between Esub(M) and Ksub(m) which has been established in previous studies (where Esub(M) is the magnetospheric convection electric field), it is possible to study the transfer efficiency of the magnetosphere. It is found that the transfer coefficient ΔEsub(M)/ΔEsub(γ) is much smaller for intense storms than for moderate ones, the latter having been studied in a previous paper (Wu Lei et al., 1981)

[en] The interpretation of statistical results derived either from studies of the field elements recorded at one or several stations or from studies of magnetic indices necessitates a knowledge of the relative influence of certain types of variations on such quantitative data. In this paper, one attempts at setting forth a morphological classification of these irregular variations and describing their main statistical laws. Two main classes are proposed: the worldwide variations and the non worldwide variations. The first class includes truly worldwide variations (Dst-type variations, ssc's and si's, worldwide fluctuations) which have a zonal component, and potentially worldwide variations (auroral variations, DP2 fluctuations) which have no zonal component. The second class includes the polar cap variations, the auroral pc5 pulsations and the solar flare effects. In conclusion, an example of a misinterpretation of results is given

[en] Through the nonlinear beating of high frequency confined waves (excited near the plasma frequency by beam plasma interaction) low frequency electrostatic forced waves are produced which may explain the characteristic features of the low frequency disturbances observed during the Araks experiments

[en] Some results of balloon measurements of the electric field in the auroral zone during quiet time and during substorms are presented. The experiments were carried out according to the Soviet-French programm SAMBO-1. The data show the values of the three components of the electric field during quiet conditions and in the 'Harang discontinuity' sector. In the midnight and morning sector during geomagnetic bays, the zonal component of the electric field exhibits significant changes: during the initial an recovery phases of the substorms, it is directed westwards, and during the active phase eastwards

[en] In this paper the results of the conjugate point experiments conducted with the Araks rockets are presented. These results are compared to conjugate point calculations using experimental and theoretical models of the magnetosphere. For the first flight good agreement is found in latitude. The agreement is not as good for the second flight when the local geomagnetic conditions were disturbed

[en] For a better understanding of the high and low frequency waves observed during the Araks experiments we present a complete investigation of the electron-beam plasma instabilities which may occur under the Araks experimental conditions

[en] Monthly mean hourly values on IQ days at Alibag for the element H have been computed for the periods 1934-1943 and 1944-1953, after applying the necessary secular and non-cyclic corrections. For each 10-year period, second degree polynomials were fitted between each of the 24 hourly series over the period and the corresponding monthly mean sunspot number (Rsub(z)). From the resultant equations the field values and their rates of variation with Rsub(z) at at each hour were computed at various levels of solar activity. The field values in both the periods showed a day-time increase and a night-time decrease with increase of Rsub(z). The rates of variation were positive for the former period and negative for the latter at Rsub(z) = 0. From these features a contribution from the asymmetric ring current has been inferred in both the periods, predominantly so in 1944-53. When the day-to-day variability in the level of the geomagnetic field has been accounted for and the computations were repeated, the corresponding results showed that (i) the field increases regularly with Rsub(z) at all hours and (ii) the rates of variation are positive at all hours for both the periods. However, in the period 1934-43 the rates of variation were found to decrease with increase of R sub (z) whereas in 1944-53 a regular increase was observed. Some possible causes for this have been suggested

[en] The stratified irregularities which appear to rise throught the equatorial F layer in the daytime have been studied at Sarh (Chad). Diurnal, seasonal and magnetic activity dependence are described on a sample of 28 months quaterhourly ionograms. The characteristics of the rise help to distinguish three subtypes. The occurrence study suggests a new physical interpretation. New and full moon epochs (+- one day) present important maxima. Autocorrelation of the intervals between days of occurrence show a clear periodic lunar background of 14 solar day period. Sharp lines peak out of these lunar maxima, but also a major peak on the solar activity 27 day interval. The luni-solar modulation and the complex variation observed are best explained by the pile-up effect to the upward drift working against a downward drift as might be expected from the polarisation due to the F region westward zonal wind. Thus our African strata occurrence seems primarily modulated by the lunarcontrolled downward drift and its associated gravity wave shears

[en] According to the measurements of pulsations and microbursts of auroral X-rays and auroras made in the stratosphere on February 25, 1974, experimental results deal with the fine temporal structure of electron precipitations in a wide energy range. The correlations between auroral X-rays power spectra and auroral luminosity are described. Some suppositions are made concerning the modulation mechanism of flow (1-5 keV) and high (50-100 keV) energy electron precipitation

[en] It has been found out that the artificial electron precipitation into the magnetically conjugated ionosphere below an altitude of 120 km leads to the formation of small-scale electron concentration inhomogeneities. The time of growth and disappearance of these inhomogeneities determined from experimental data does not exceed 20 msec. These estimates and the results of spectral analysis of the radar echo intensity variations have led to the conclusions that (1) the observed anomalous delays in the occurence of radar echoes were caused by delays of electron precipitations into the ionosphere below 120 km, and (2) the energy of the main part of precipitated electrons was close to the injection energy