Showing papers in "Earth, Planets and Space in 1980"

An interpretation of paleomagnetic results from Cretaceous granites in South Korea.

Abstract: The mean virtual pole position for the Cretaceous granites in South Korea is close to the present geographic pole and is consistent with that for Cretaceous, Pliocene and Pleistocene volcanic rocks from the same region. It also accords with pole positions obtained from Chinese, Siberian and European Cretaceous rocks. From the paleomagnetic data for the granites and volcanic rocks of the Cretaceous, it is concluded that the South Korean land mass has not been subjected to sufficient local tectonic movements to generate a change in the direction of primary magnetic vectors of the granites or of the volcanic rocks since the Cretaceous. This means that although some tectonic movement has taken place in South Korea since the Cretaceous, the movement brought about only vertical block displacements with no significant tilting or rotational movements. It also suggests that the virtual geomagnetic pole for the Cretaceous rocks in South Korea provides a valid Cretaceous virtual pole position for the Eurasian land mass.

Propagation of tsunami on a linear slope between two flat regions. Part II reflection and transmission.:PART II REFLECTION AND TRANSMISSION

Abstract: Reflection and transmission of long sinusoidal tsunami waves are investigated for a sea with a linearly sloping region sandwitched by a flat shelf and an outer ocean having a constant depth. Both the coefficients are derived as a function of period, incident angle and dip angle. It is found that the coefficients strongly depend on the period of incident wave and that the existence of a slope affects the tsunami wave form. Particularly, a gentle slope contributes a selective reflection and transmission of wave component of tsunami. The ratio of the amplitude at the coast to that of the incident wave from the outer sea was also investigated taking into account of a rigid coast. It is noted that the only resonance period amounting to 70min is expected in the case of north east Japan.

Small-scale fluctuations in the HF-Doppler signals of the F-region ionosphere over central Japan.

Abstract: From the beginning of 1976 the standard type CW Doppler sounder at Sugadaira has been used to study the spectra of frequency shifts of the Doppler echoes from the F-region ionosphere over central Japan. Some of the obtained data samples, with interpolated sections, are subjected to maximum entropy spectral analysis. The resultant power spectrum densities have revealed that the small-scale fluctuations of the Doppler signals contain several dominant periods in the range of 4 to 98min.

Study of lower ionospheric absorption in terms of contributions from solar fluxes in different wavelength bands.

Abstract: Noontime absorption on 1.8, 2.0, 2.2 and 2.5MHz at Trivandrum (magnetic dip -0.6°S) can be expressed in terms of solar X-ray and 10.7cm (F10.7) fluxes and the noontime solar zenith angle by an empirical relation. The components of absorption related to X-ray, F10.7 and the component independent of these two as obtained from the empirical relation have been examined on the basis of theoretical estimates of contributions to absorption from EUV, X-ray and Lyman-α solar fluxes. The solar activity independent component in the empirical relation is found to agree with the contribution from the solar activity independent component of solar Lyman-α radiation. From the theoretical analysis it has been shown that the wavelength range of solar X-ray effect on absorption for which 1-8A integrated X-ray flux will be a good representative index is 1A to 30-35A.

Low Frequency Pulsation Generation by Energetic Particles

Abstract: We review some ideas developed over the past decade about the generation of low frequency waves in the magnetosphere by wave particle resonance. We emphasise the importance of wave symmetry about the equator, the particular type of particle distributions present in the magnetosphere and differences between drift and bounce resonance. Many arguments are independent of the precise wave mode. Later in the paper we concentrate on the problem of Alfven wave generation by ring current protons. Recent analysis of measurements at synchronous orbit have yielded supporting experimental evidence.