A study is made of movements in the Es region by means of measurements of pulsed waves at 1.85Mc/s emitted from a Loran station and of ionospheric vertical soundings.
Moving clouds in the Es region of large lateral dimensions are usually observed during the night either isolated or grouped like the wavy clouds sometimes seen in the troposphere. The speed of about 80m/sec and the direction towards the southwest are deduced from various kinds of observations.
It is inferred from this experiment that the observed Es layer is of two types: the first is the horizontally stratified thin layer produced by electromagnetic re-distribution due to the laminar wind shear and the second consists of a number of elongated regions of excess ionization, being of the order of 100km long and 10km wide, which may be caused by hydrodynamical instability in the wind shear prevailing there.

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Characteristics of the three-dimensional hydromagnetic waves caused by the local source in a uniform cold plasma are studied. There are two modes of hydromagnetic waves. The one is an isotropic mode which spreads in all directions from the source and transmits the disturbance of magnetic field component parallel to field lines. The other is a mixed transverse mode consisting of two parts, the pure and the converted transverse modes, and communicates the signals of normal components of fields. It is emphasized that the former part is a one-dimensional wave propagating parallel to lines of force through the source region, while the latter is the converted one-dimensional wave from the three-dimensional isotropic mode with the geometrical attenuation. The space-time relations of disturbances belonging to the converted mode are obtained. The structures of hydromagnetic waves generated by the particular external forces, the partial compression and the azimuthal drag, are also presented. In a case of reflection of the transverse wave on the anisotropic conducting sheet, the quantitative relation between the incident electric field and the induced currents in the sheet is shown. Furthermore, space and time variations of hydromagnetic oscillations excited by the azimuthal stress and confined within the region between two parallel infinitely conducting solid are illustrated. With relation to the characters of three-dimensional hydromagnetic waves, qualitative discussion on some geomagnetic disturbances are given.

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Mechanisms of pc 2, 3 (5-40sec), pc 4 (40-150sec) and pc 5 (150-900sec) are studied. More than 6, 000 series of continuous pulsations are analyzed from the magnetograms at Fredericksburg, Byrd Station, Yakutsk, Onagawa and other auxiliary 20 stations. Results are summarized as follows:
1) Geomagnetic micropulsations of pc 4 and pc5 are caused by hydromagnetic standing oscillations along the geomagnetic field-lines, while pc 2, 3 are induced by hydromagnetic standing oscillation below the region of maximum Alfvén wave velocity. The disturbed region on the frontal surface of the earth's cavity generated by solar wind would be the source of the hydromagnetic waves responsible for the pulsations.
2) The world-wide shape of the base of the protonosphere surrounding the earth is inferred from the distribution of pc 2, 3 period, namely, an inverted U-type diurnal variation and a latitudinal dependence of the period. The various types of pc 2, 3 activity diurnal variation (M-, N- and A-types) and of its seasonal variation (S-, E- and C-types) may be due to the F2 control and the axial effect of the sun.
3) As for pc 4 and pc 5, a clear U-type diurnal variation in period seems to be attributed to the day-side compression of the geomagnetic field-line by solar wind.
4) Non-seasonal annual variations in the pc 4 and pc 5 periods are detected. It is found that the non-seasonal variations are related closely with those in whistler dispersion, satellite drag, f₀F2 and f₀E. Among several possibilities of the mechanism, the effect of the elipticity of the earth's orbit on the ionospheric density is deemed the most dominant cause of the common non-seasonal variation. It is stressed that pc 4 and pc 5, like whistlers, have powerful competence for exploring the physical state of the exosphere by considering both diurnal and seasonal variations between whistlers and pc's 4 and 5 phenomena.

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Radio noise data obtained with the CRPL model ARN-2 noise recorder at Byrd Station, Antarctica, during blizzards are analyzed. The noise power data are used to determine some of the characteristics of snow static in the frequency range 0.51 to 20Mc/s. The frequency dependence of snow static and its relation to wind speed are established. Magnitude of the noise intensity decreases with increasing frequency from 0.51 to 5Mc/s. Snow static during blizzards is apparently caused by point discharge when the electrostatically charged blowing snow particles strike the unshielded receiving antenna. It is shown that measurements utilizing radio techniques with exposed antennas may be seriously affected by snow static during Antarctic blizzards.

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