FULL-WAVE CALCULATION OF ELF VLF PROPAGATION FROM A DIPOLE SOURCE LOCATED IN THE LOWER IONOSPHERE

A full wave technique has been developed to calculate the field intens ities both in the upper ionosphere and on the ground when a dipole sou rce immersed in the lower ionosphere radiates ELF/VLF waves. The radia ted wave is divided into a large number of elementary plane waves, for each of which the propagation in the horizontally stratified model co nsisting of the ionosphere, the free space and the ground is calculate d by the full wave technique. Then the plane waves are summed up to gi ve a horizontal distribution of the radiated wave intensities at any a ltitudes. This technique is applied to investigate the propagation cha racteristics of radiation from a polar electrojet (PEJ) antenna modula ted at an ELF/VLF frequency, which was created by the Tromso heating f acility. Comparison between the results of experiments and the calcula tion is given in the companion paper [Kimura et al., this issue]. We d iscuss several propagation characteristics, such as the frequency depe ndence of the radiated wave propagation up to the upper ionosphere and down to the ground. Under the conditions that the frequency is 2.5 kH z and the ionospheric dc electric field is 5 mV/m, the calculated resu lts are roughly consistent with the experimental results and the radia tion efficiency of the PEJ antenna is found to be extremely small, 2.5 x 10(-6) upward and 3 x 10(-8) downward.