The 3‐D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere

Abstract

We present 3-D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high-frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography-like 3-D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, 5,577, and 8,446 Å. Inspection of the 3-D reconstructions suggests that the distribution of energized electrons is less extended in altitude than predicted by transport calculations of electrons accelerated to 2-100 eV. A possible reason for this discrepancy is that high-frequency pumping might induce an anisotropic distribution of energized electrons.Plain Language Summary Auroral lights can be artificially generated by transmitting high-frequency radio waves with high power into the upper atmosphere. In this article, we use multiple viewpoint imaging of artificially produced aurora to estimate the 3-D distribution of the auroral lights by employing tomography-like techniques. The 3-D distribution is estimated in the red, green, and infrared auroral emission lines with wavelengths of 630.0, 557.7, and 844.6 nm, respectively. These emissions are excited by energetic electrons, which have been accelerated through interaction processes between the transmitted radio waves and plasma in the upper atmosphere, at an altitude of about 220-250 km. We observe that the estimated 3-D auroral distributions are less extended in altitude than indicated by previous theoretical work. A possible reason for this disagreement is that the radio wave-plasma interaction processes might lead to a direction dependent electron acceleration.

Evaluation of the effectiveness of energetic thermal electrons on the excitation of the ionospheric red 6300 Å airglow

“…Bibliography has plenty references to respective plots. Indicatively, we mention some cases: (i) the large airglow intensity enhancements in the highlatitude ionosphere, showed in figure 3 of [29], (ii) the airglow intensity enhancements in the mid-latitude ionosphere, as showed in figure 1 of [30], in figures 4 and 5 of [3], and in figures 2 and 7 of [31].…”

“…It would also be interesting to investigate the thermal electron contribution on the green airglow emission in order to evaluate its magnitude, compared to other excitation mechanisms which act additionally or competitively, although a priori we expect this contribution to be less than the non-linear ones [29] as a thermal electron energy distribution does not include enough electrons with energies greater than 4.17 eV to induce the respective enhancements at λ = 5577 Å.…”

“…At the [29] the scientists radiated the F region of the ionosphere firstly with a frequency away from a gyroharmonic and a 138.2 MW Effective Radiated Power (ERP), and then with a frequency in proximity to the fourth gyroharmonic frequency and a 115.9 MW ERP. Both the ERPs are well above the [28]'s, so unsurprising greater airglow intensities than those of [28] are now observed.…”

UVI Image Segmentation of Auroral Oval: Dual Level Set and Convolutional Neural Network Based Approach

“…The aurora images captured by these two instruments are shown in Figure 1. Different from the ground-based observation, auroral images captured by UVI instruments in the space mainly focus on providing global information, e.g., the overall configuration of the aurora and the spatial distribution of the auroral intensity [5,6] In the last few years, the extraction of auroral oval attracts huge interests of geophysicists due to its usefulness to monitor the geomagnetic activity and research the physical mechanism of the solar wind-magnetosphere-ionosphere coupling process [2,3,[7][8][9][10][11]. The exact location of the auroral oval's equatorward boundary depends on the magnetospheric electric and magnetic fields.…”

Automatic Auroral Boundary Determination Algorithm With Deep Feature and Dual Level Set

“…The Earth's auroral emissions are the results of collisions with the neutral constituents in the ionosphere of the precipitating charged particles from the solar wind (Boudouridis et al, 2003; Kvammen et al, 2019; Qian et al, 2011). In the observation of ground‐based and satellite‐borne imager instruments, the aurorae are roughly circular belts located around the geomagnetic poles and also known as auroral ovals (Akasofu, 1965; Hu et al, 2017; Qian et al, 2011).…”