Hui Li

This paper has established a relatively comprehensive model for ultra-low frequency (ULF) current induced by thermal pressure gradients and its propagation. In the ULF current excitation model, we decomposed the current into a constant term unaffected by altitude and a product with a function significantly influenced by altitude. Combining this with the EISCAT background, we determined that for modulation frequencies below 5 Hz, the optimal height for ULF current excitation corresponds to the critical frequency height. We calculated the ionospheric currents at heating altitudes of 332 km for modulation frequencies of 5 Hz; the corresponding maximum currents were 1.03 × 10−10 A·m−2. By incorporating the current into the ULF waves propagation model based on magnetoionic theory, we found that the electromagnetic field energy is mainly concentrated in the horizontal direction, indicating that the energy primarily propagates outward through magnetosonic waves. The dominant components are the electric field component Ey and the magnetic field component Bz, whose maximum values reached 1.1 μV·m−1 and 1.5 pT. Unfortunately, magnetosonic waves cannot propagate downward due to the sharp variation in the real part of the refractive index between 200 and 300 km. However, the shear Alfvén waves component By can propagate downward, and there is still an intensity of approximately 0.1 pT at the bottom of the ionosphere, which is because the refractive index of shear Alfvén waves is most uniform in the parallel magnetic field direction, allowing By to propagate parallel to the magnetic field effectively.

The paper starts from the polarization of the electromagnetic wave launched by the transmitter, develops an ionospheric heating model for a wide range of launching angles and polarizations of powerful heating radio waves. The electric field polarization is characterized by Q and ϕ, where Q characterizes the relative amplitude of the electric field components and ϕ characterizes the relative phase of the electric field components. We use similarity transformation and tensor calculation in our calculations and give the optimal polarization equation using the idea of finding the maximum value of a binary function. Combining the ionospheric background data of three widely separated locations—EISCAT (polar region), Beijing (mid-latitude), and Sanya (low latitude)—we have numerically calculated and discussed the three sites based on the heating model. The following conclusions are drawn from the calculations. The Q of the optimal polarization gradually decreases and tends to be stable when the collision frequency becomes negligible relative to the ionospheric cyclotron frequency. Q also depends on the angle between the radio wave launching angle and the magnetic inclination angle. The optimal polarization angle ϕ is generally π/2 in northern hemisphere heating experiments. With the angle between the radio wave launching angle and the magnetic inclination angle increasing from 0, the optimal polarization changes from left-handed circular polarization to left-handed elliptical polarization, and when it reaches π/2, the optimal polarization becomes east–west linear polarization. These results will provide some guidance in future experiments.

Based on the continuity and momentum equations, a self-consistent simulation model is developed for describing the localized electron density enhancement caused by high-pressure H2O gas release in the ionosphere. The chemical reaction and momentum exchange process between the neutral gas and ionospheric plasma species are considered in the theoretical simulation model. The finite element method is used to solve the simulation model for H2O gas release, and the expansion and ionospheric disturbance process at the early stage of high-pressure gas release are studied. It is shown that the space expansion of the released gas is mainly dominated by the pressure difference between the H2O gas and the ionospheric plasma at the early stage of release. Then the diffusion process becomes the dominant process of the space transport of H2O molecules. An electron depletion region forms near the center of the release region due to the chemical reaction and collision process with H2O molecules. Meanwhile, an electron density enhancement region forms on both sides along the magnetic field direction due to the electron snowplow effect. With the increase in the released mass of H2O gas, the intensity and duration of the electron density enhancement increase gradually. With the release position rising, it is found that the intensity of the electron density enhancement has a peak near 380 km and the duration increases slightly with the increasing release height.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature ΔT_e is about 570 K, and the ratio is ΔT_e / T_e ~48 %. The maximum drift current density is 8 × 10⁻¹⁰ A ⋅ m⁻², and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle.