A Study On ELF/VLF Wave Propagation Estimated In High Altitude Area Ionospheric Heating Experiments

In recent decades years,with the great improvement of radar facilities and the data-analyzing technique,the ionospheric heating experiments are in the boom. Many important heating effects are discovered, in which the Extremely-Low-Frequency(ELF) and Very-Low-Frequency(VLF) radiation as the result of current modulation attracts more attention because of its important application in the marine communication. On the basis of Ohmic heating theory, this article briefly studies the production of ELF/VLF waves and the propagation of downward propagation whistler mode waves in the earth-ionosphere waveguide in system. The main results obtained are summarized as follows:The ionosphere conductance is in tensor as the result of geomagnetic field, and the distribution chatacteristics of electron density, collision frequency and the conductivity tensor with height are presented. Ohmic heating theory which plays a major role in the lower ionosphere heating experiments is given. Much importance is put on the disposal of the data got by incoherent scatter radar from the heating experiments on November 2011 by China in Norway, and the heating effects on electron temperature(Te) and electron density(Ne) under different heating modes are studied. Data analysis shows that the electron temperature and electron density within a certain height range produced a significant increase during the heating period, which reconvert soon after heating turned off. In lower ionosphere, X modes heating cause more obvious heating effects, while in high ionosphere it is O mode. The conductivity tensor during heating period are calculated.Based on the electron energy equation, a model of ionospheric amplitude-modulated heating is established. The height distributions of energy absorption rate and loss rate of the high latitudes ionosphere are studied. The producing mechanism of ELF/VLF radiation is introduced and the process of the formation of ELV/VLF antenna is analyzed theoretically. The time evolution characteristics of the electron temperature and the components of the conductivity tensor are calculated and simulated, as well as the conductivity disturbance. Analysis of experimental data also finds that the conductivity produced a periodic disturbance. Simulation finds that the impact on thePedersen conductivity of modulation frequency is greater than Hall conductivity. Pedersen conductivity decreases with the increase of modulation frequency, while the Hall conductivity changes little. By temperature control, temperature variation characteristics of Pedersen conductivity and the Hall conductivity are similar. If the modulation frequency is relatively large, it is OK to just consider the role of Hall conductivity on the formation of ELF / VLF antenna;Derivation finds the radiation source generated at high latitudes can be equivalent to a horizontal electric dipole. Only near vertical downward propagation of the extraordinary wave can enter the atmosphere. With Fourier transform and inverse transform and boundary conditions, and the use of quasi-longitudinal approximation, we calculate the field nearby sea radiated by source up in ionosphere, which is of the order of 10-7A/m. The propagation effects under different modulation frequency are researched. In a whole, low-frequency modulation effects are better. As a result of the interference, there will be a number of maximum and minimum points on the field;Parabolic equation(PE) method is used in propagation problem of ELF/VLF wave in earth-ionosphere waveguide. Way propagation loss and the field intensity distribution of the longitudinal and transverse direction under different frequency are calculated, with a depart path of refraction index under the use of backward departed mixed fourier transform(DMFT). It is found that in the distant dissemination process, loss in the vicinity of the ground and the ionosphere is larger, and in the air is smaller;Mode theory is used to calculate the field of a level electric dipole in earth-ionosphere waveguide. The effect of geomagnetic field is considered and the impedance of lower ionosphere boundary and earth boundary is presented.