Low Frequency Waves During RF Heating of the Ionosphere: Numerical Simulations (original) (raw)
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Low-Frequency Waves . Generated . by . HF Heating . of . Mid-Latitude Ionosphere
2015
High frequency (HF) heating of the ionsosphere excites hydromagnetic waves which propagate to the ground and into the magnetosphere. In the mid-latitude ionosphere, modulated HF heating in the F-region produces a local fluctuating electron temperature, and the resulting pressure gradient leads to a diamagnetic current which excites magnetosonic waves. In the E-region, where the Hall conductivity is dominant, these waves lead to oscillating Hall currents that produce shear Alfvén waves. The excitation of hydromagnetic waves in the mid-latitude ionosphere is simulated using Hall MHD model and taking into account the Earth’s dipole magnetic field. With the heating in a region located at L = 1.6, altitude of 500 km and HF waves modulated at 2 – 10 Hz, the waves are generated by processes similar to the high-latitude case. The shear Alfven waves propagating to the magnetosphere become electromagnetic ion cyclotron waves at higher altitudes and propagate to the ion cyclotron resonance layer.
Radiophysics and Quantum Electronics, 2011
We present the results of coordinated satellite and ground-based observations of the high-latitude ionospheric phenomena induced by high-power high-frequency (HF) radio waves. The ion outflow phenomenon accompanied by a strong increase in the electron temperature and thermal expansion of plasma was observed in the evening hours, when the high-latitude ionospheric F region was heated by high-power O-mode HF radio waves. The DMSP F15 satellite recorded an increase in the ion number density O + at an altitide of about 850 km in that period. Ultralow-frequency (ULF) radiation at the modulation frequency 3 Hz of the high-power HF radio waves, which was generated in the ionosphere irradiated by high-power O-mode HF radio waves and accompanied by a strong increase in the electron temperature and the generation of artificial small-scale ionospheric irregularities, was recorded by the CHAMP satellite during the heating experiment in Tromsø in November 5, 2009. The results of the DEMETER satellite observations of extremely low frequency (ELF) radiation at the modulation frequency 1178 Hz of the high-power radio waves in the heating experiments were analyzed using the event of March 3, 2009 as an example.
Radiophysics and Quantum Electronics, 2011
We present the results of multi-instrument experiments related to studying the phenomena in the high-latitude ionosphere affected by high-power radio waves using the EISCAT technical facilities. It was found for the first time that strong small-scale artificial field-aligned irregularities (AFAIs) are excited when the ionospheric F region is heated by a high-power HF radio wave with X-mode polarization near the altitude at which the critical frequency f xF 2 of the F 2 layer is equal to the frequency f H of the heating accompanied by an up to 50% increase in the electron temperature. The spatial structure of the artificially perturbed ionospheric F region is examined in detail using an incoherent scatter radar operated in the regime of scanning over elevation angles from 92 • to 74 • with a 2 • step. It is shown that the spatial size of the heated patch strongly depends on the angle of the HF pumping relative to the Earth's magnetic field. The phenomena occurring in the artificially modified ionospheric F region heated at frequencies near the third electron gyroharmonic, i.e., at f H = 3f ce = f UH , where f UH is the upper-hybrid frequency, are explored on the basis of multi-instrument observation data.
Generation of ELF waves during HF heating of the ionosphere at midlatitudes
Radio Science
Modulated high-frequency radio frequency heating of the ionospheric F region produces a local modulation of the electron temperature, and the resulting pressure gradient gives rise to a diamagnetic current. The oscillations of the diamagnetic current excite hydromagnetic waves in the ELF range that propagate away from the heated region. The generation of the waves in the 2-10 Hz range by a modulated heating in the midlatitude ionosphere is studied using numerical simulations of a collisional Hall-magnetohydrodynamic model. To model the plasma processes in the midlatitude ionosphere the Earth's dipole magnetic field and typical ionospheric plasma parameters are used. As the hydromagnetic waves propagate away from the heated region in the F region, the varying plasma conditions lead to changes in their characteristics. Magnetosonic waves generated in the heating region and propagating down to the E region, where the Hall conductivity is dominant, excite oscillating Hall currents that produce shear Alfvén waves propagating along the field lines into the magnetosphere, where they propagate as the electromagnetic ion cyclotron (EMIC) and whistler waves. The EMIC waves propagate to the ion cyclotron resonance layer in the magnetosphere, where they are absorbed.
2018
High frequency (HF) heating of the ionsosphere excites hydromagnetic waves which propagate to the ground and into the magnetosphere. In the mid-latitude ionosphere, modulated HF heating in the F-region produces a local fluctuating electron temperature, and the resulting pressure gradient leads to a diamagnetic current which excites magnetosonic waves. In the E-region, where the Hall conductivity is dominant, these waves lead to oscillating Hall currents that produce shear Alfvén waves. The excitation of hydromagnetic waves in the mid-latitude ionosphere is simulated using Hall MHD model and taking into account the Earth’s dipole magnetic field. With the heating in a region located at L = 1.6, altitude of 500 km and HF waves modulated at 2 – 10 Hz, the waves are generated by processes similar to the high-latitude case. The shear Alfven waves propagating to the magnetosphere become electromagnetic ion cyclotron waves at higher altitudes and propagate to the ion cyclotron resonance layer.
Radiophysics and Quantum Electronics, 2012
We present the results of modifying the F 2 layer of the polar ionosphere experimentally with highpower HF extraordinary-mode waves. The experiments were performed in October 2010 using the short-wave SPEAR heating facility (Longyearbyen, Spitsbergen). To diagnose the effects of high-power HF waves by the aspect-scattering method in a network of diagnostic paths, we used the short-wave Doppler radar CUTLASS (Hankasalmi, Finland) and the incoherent scatter radar ESR (Longyearbyen, Spitsbergen). Excitation of small-scale artificial ionospheric irregularities was revealed, which were responsible for the aspect and backward scattering of the diagnostic signals. The measurements performed by the ESR incoherent scatter radar simultaneously with the heating demonstrated changes in the parameters of the ionospheric plasma, specifically, an increase in the electron density by 10-25% and an increase in the electron temperature by 10-30% at the altitudes of the F 2 layer, as well as formation of sporadic ionization at altitudes of 140-180 km (below the F 2 layer maximum). To explain the effects of ionosphere heating with HF extraordinary-mode waves, we propose a hypothesis of transformation of extraordinary electromagnetic waves to ordinary in the anisotropic, smoothly nonuniform ionosphere.
The magnetic response of the ionosphere to pulsed HF heating
Geophysical Research Letters, 2005
It shown theoretically and confirmed for the first time experimentally that the magnetic response of the lower auroral ionosphere to pulsed ionospheric HF heating depends critically on the parameter T/T h , where T is the pulse duration and T h is the time required for the electron temperature to reach its steady state value. Theoretical analysis shows that the strength and pulse shape of the near-zone magnetic field on the ground depends not only on the traditional quasi-static near-field term, but also on a term which depends on the derivative of the current (i.e., the impulse response of the ionosphere). Results from newly-conducted experiments using the HAARP transmitter in Gakona, Alaska are presented that verify our model, and it is shown that for T T h the magnetic flux on the ground due to the impulse response is 10-15 dB larger than the flux due to the quasistatic term.
Generation of ELF and ULF electromagnetic waves by modulated heating of the ionospheric F2 region
Journal of Geophysical Research, 2012
We present a theoretical and numerical study of the generation of extremely low frequency (ELF) and ultra-low frequency (ULF) waves by the modulation of the electron pressure at the F2-region with an intense high-frequency electromagnetic wave. The study is based on a cold plasma Hall-MHD model, including electron-neutral and ion-neutral collisions, which governs the dynamics of magnetostatic waves and their propagation through the ionospheric layers. Magnetosonic waves generated in the F2 region are propagating isotropically and are channeled in the ionospheric waveguide, while shear Alfvén waves are propagating along the magnetic field. To penetrate the ionosphere from the F2 peak at 300 km to the ground, the magnetostatic waves first propagate as magnetosonic or shear Alfvén waves that encounter a diffusive layer from about 150 km to 120 km where the Pedersen conductivity dominates, and then as helicon (whistler-like) mode waves from about 120 km to 80 km where the ions are collisionally glued to the neutrals and the Hall conductivity dominates. By performing numerical simulations and studying the dispersive properties of the wave modes, we investigate the dynamics and penetration of ELF/ULF waves through the ionospheric layers to the ground and along the geomagnetic field lines to the magnetosphere. Realistic profiles of the ionospheric profiles of conductivity and density are used, together with different configurations of the geomagnetic field, relevant for both the high, mid and equatorial latitudes. Some of the results are compared with recent HAARP experiments.