An improved matrix method of calculating the solutions of wave equations in a horizontally stratified anisotropic medium is described. An inhomogeneous medium is divided into a number of thin horizontal and homogeneous slabs. The solutions of a differential equation with constant coefficients in each slab are connected by applying the boundary conditions, and the wave fields are given as the power series expansion of wave fields. In calculating the wave fields, a matrix is divided into two matrices for two independent solutions and Gram‐Schmidt orthogonalizing process is applied to prevent numerical swamping. Comparisons are made between this and other full wave methods regarding step size and computer time, and this method is found to be more efficient than the full wave method especially at high frequency wave fields. The magnetoionic modes separated from the resultant wave are shown for a model ionosphere.
Short-period disturbances of the ionosphere were observed by a network of HF Doppler receivers in central Japan at the time of typhoons 18 and 19 which crossed the Islands of Japan successively in September 1982.Both dynamic and static spectral analyses on sample records revealed that (1) these waves have the periods ranging between 1.4 and 9.7 min that correspond to infrasound at F-layer heights (and partly to gravity wave at E-layer heights), (2) the spectral content varies from hour to hour, from station to station for a given typhoon, and further one typhoon to the other, and (3) the spectral fine structure does not accord with existing theoretical prediction for thunderstorms. It is, therefore, plausible that the observed spectral peaks arose from the characteristics of the radiation sources in the typhoon air mass.Horizontal and vertical phase velocities, and corresponding wavelengths of the ionospheric waves were also measured using cross-correlation method. It is shown that (1) the horizontal phase velocities take similar values to those observed during the severe thunderstorms and tornadoes so far reported, with scatter range of the values being slightly larger than the latter two, and (2) the mean values of the upward vertical phase velocities are several to ten times larger than those of the horizontal ones.
A method of estimation of the collision frequency in the lower ionosphere using the field intensity of a ground based LF signal observed by a rocket is described. The magnetic intensity profiles, in the ionosphere, of a ground based signal observed by a rocket and the electron density simultaneously observed at several altitudes are analyzed by iterative calculations based on a simple WKB solution. The collision frequency for mono-energetic electrons, vm, in the upper D and E regions was actually estimated from the altitude profile of the right handed circularly polarized component of a 40kHz ground based signal observed by means of theK-9M-53 rocket. As a result, the following relationships were obtained; Vm=4.8x105P for the upper D region and vm=11.0x105P for the E region, where P(Newton/m2) was taken from CIRA (1972).
The full‐wave analysis method is described for computing the electromagnetic field on the ground when a beam‐shaped wave is incident from above the ionosphere. By means of this method, the directional error was evaluated in various VLF direction finders which measure the exit point of the natural wave at the lower portion of the ionosphere, under the assumption that the downgoing wave is radiated from a duct. In this method, the directional errors due to multiple reflection, polarization, beam wave of the arriving radio wave and the type of ionospheric models can be found systematically so that a simulation result most resembling the practical situation is provided. The main results are as follows: (1) When the transmission cone is within the trapping cone, the NPF method using orthogonal loop antennas and vertical antennas can indicate an almost correct direction within a radius of about 100 km from the maximum point of the radiowave strength on the ground. The error increases at a distance of more than 150 km. On the other hand, the Poynting method indicates almost correct directions even at a distance of more than 200 km regardless of the polarization. The goniometer method has almost the same accuracy as the Poynting method; (2) if the overlapping of the transmission cone and the trapping cone is smaller, the error is increased in the south direction in all three methods; and (3) no significant frequency dependence is observed in the directional error.
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