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Abstract The strong very high frequency (VHF) radiation from compact intra‐cloud discharges (CIDs) is attributed to streamers. An analytical model, taking altitude and applied electric field as input, is developed for effective representation of current for a double‐headed exponentially growing streamer. The decay of streamer current is attributed to two‐ and three‐body attachment of electrons to molecular oxygen. The model predicts streamers of growing strength and spatial scales at altitudes where electron losses due to three‐body attachment are suppressed with reducing air pressure. We show that CIDs at higher altitudes develop during a longer period such that the spectral content of recorded sferics shifts toward lower frequencies. The model is used to interpret the recorded sferics of two CIDs originating from km altitude in terms of radio signals emanating from an ensemble of streamers. The driving thundercloud electric fields are found to be , where is conventional breakdown threshold field. 

Abstract The time dynamics of positive corona ignition from an initial seed electron to the appearance of space charge effects is studied at atmospheric pressure in a spherically symmetrical geometry. The time-dependent model incorporates a recent photoionization model and boundary conditions to properly treat the corona discharge in the proximity of the anode surface. The applied voltage satisfying the self-sustainability condition of the discharge is first calculated. Then, the time dynamics of the discharge is studied for higher and lower applied voltages. The exponential growth in electron density is identified before space charge effects significantly shield the applied electric field. The related characteristic time of exponential growth in electron density is calculated as a function of applied voltage. The time scale can be tens of nanoseconds when applied voltage is close to the threshold or less than one nanosecond when increasing voltage 10% above the threshold for atmospheric pressure. Analogous to the equality of ionization timescale and dielectric relaxation time in stable streamers, a characteristic timescale is used to predict the behavior of the discharge. When the characteristic time is about one-tenth of the dielectric relaxation time, a one-tenth reduction in the applied field on the anode is observed. As the dielectric relaxation time drops below ten times the characteristic time, the discharge behavior diverges for different applied voltages, and the characteristic time is not a good predictor of further discharge dynamics. 

Abstract We revisit the problem of photoionization of small admixtures of nitrogen and oxygen molecules in atmospheric pressure helium plasma originally formulated in the pioneering work of Naidis (2010J. Phys. D: Appl. Phys.43402001). The radiation trapping of resonance emission lines in atomic helium is quantified, and it is demonstrated that photoionization occurs due to radiative decay of the electronicAstate of helium molecules. The collisions and atomic precursors that populate the excitedAstate of the helium molecule are clearly identified. The Einstein probabilities for the transition from bound and quasi-bound rovibrational levels of theAstate to the continuum of the groundXstate are provided. A kinetic scheme for the production of the fast component of ultraviolet emissions in atmospheric pressure helium plasma is proposed. The photoionization of molecular oxygen and molecular nitrogen as impurities in 99.9% and 99.99% purity helium is studied. 

Abstract Recent studies suggest that, despite its aurora‐like appearance, the picket fence may not be driven by magnetospheric particle precipitation but instead by local electric fields parallel to Earth's magnetic field. Here, we evaluate the parallel electric fields hypothesis by quantitatively comparing picket fence spectra with the emissions generated in a kinetic model driven by local parallel electric fields energizing ambient electrons in a realistic neutral atmosphere. We find that, at a typical picket fence altitude of 110 km, parallel electric fields between 40 and 70 Td (∼80–150 mV/m at 110 km) energize ambient electrons sufficiently so that, when they collide with neutrals, they reproduce the observed ratio of N₂first positive to atomic oxygen green line emissions, without producing first negative emissions. These findings establish a quantitative connection between ionospheric electrodynamics and observable picket fence emissions, offering verifiable targets for future models and experiments. 

Abstract We present a theory based on the conventional two-term (i.e. Lorentzian) approximation to the exact solution of the Boltzmann equation in non-magnetized weakly ionized plasma to efficiently obtain the electron rate and transport coefficients in a magnetized plasma for an arbitrary magnitude and direction of applied electric field $\vec{E}$and magnetic field $\vec{B}$. The proposed transcendental method does not require the two-term solution of the Boltzmann equation in magnetized plasma, based on which the transport parameters vary as a function of the reduced electric field $E/N$, reduced electron cyclotron frequency ${\omega }_{\mathrm{c}\mathrm{e}}/N$, and angle $\mathrm{\angle }\vec{E},\vec{B}$between $\vec{E}$and $\vec{B}$vectors, whereNis the density of neutrals. Comparisons between the coefficients derived from BOLSIG+’s solution (obtained via the two-term expansion when $\vec{B}\ne 0$) and coefficients of the presented method are illustrated for air, a mixture of molecular hydrogen (H₂) and helium (He) representing the giant gas planets of the Solar System, and pure carbon dioxide (CO₂). The new approach may be used in the modeling of magnetized plasma encountered in the context of transient luminous events, e.g. sprite streamers in the atmosphere of Earth and Jupiter, in modeling the propagation of lightning’s electromagnetic pulses in Earth’s ionosphere, and in various laboratory and industrial applications of nonthermal plasmas. 

Abstract Sharp point electrodes generate significant electric field enhancements where electron impact ionization leads to the formation of electron avalanches that are seeded by photoionization. Photoionization of molecular oxygen due to extreme ultraviolet emissions from molecular nitrogen is a fundamental process in the inception of a positive corona in air. In a positive corona system, the avalanche of electrons in the bulk of the discharge volume is initiated by a specific distribution of photoionization far away from the region of maximum electron density near the electrode where these photons are emitted. Here, we present a new approach to finding the inception conditions for a positive corona, which is based on a differential formulation of the photoionization problem. The proposed iterative solution considers the same inception problem that has been solved in the existing literature by using either an integral approach to photoionization or a differential formulation of photoionization and considering the inception problem as a boundary-value eigenvalue problem. The results are validated by comparisons with previous integral formulations and time dynamic plasma fluid solutions in planar and spherical geometries. The results illustrate ideas advanced in Kaptzov (1950Elektricheskiye Yavleniya v Gazakh i Vacuumep 610) providing a physically transparent connection between an effective secondary electron emission coefficient due to volume photoionization in a positive corona system and the secondary electron emission in conventional Townsend discharge theory. The results also demonstrate the significance of boundary conditions for accurate corona solutions that are based on a differential formulation of photoionization. 

Abstract Terrestrial gamma ray flashes (TGFs) are high‐energy photon bursts that have been linked to short bursts of electromagnetic radiation associated with lightning activity. The most puzzling unexplained aspect of these events is that gamma rays originate from very compact regions of space while the source regions often seem to be optically dim and radio silent when compared to processes in ordinary lightning discharges. In this work, we report a mechanism that allows precise quantitative explanation of these peculiar features of TGFs and their relationships to the observed waveform characteristics of associated radio emissions. The mechanism represents an extension of earlier ideas on feedback processes in growth of relativistic runaway electron avalanches (Dwyer, 2003,https://doi.org/10.1029/2003GL017781), and is based on a recent demonstration of the dominant role of the photoelectric feedback on compact spatial scales (Pasko, Celestin, et al., 2023,https://doi.org/10.1029/2022GL102710). Since discussed events often occur in isolation or precede formation of lightning discharges, the reported findings propose a straightforward solution for the long‐standing problem of lightning initiation. 

Abstract In this work the electric field of narrow bipolar events (NBEs) measured at a remote location is used to extract the current waveform of the source discharge. All calculations correspond to a vertical linear current source above a perfectly conducting ground plane. The current study uses the well established formulation of electromagnetic fields in the frequency domain, and develops a deconvolution based technique to obtain exact reconstruction of the source current, improving upon previous modeling of NBEs, which often require tuning several inter‐dependent parameters to determine the current that best reproduces the observed electric field. Our proposed solution, although readily available in standard electromagnetic textbooks, has never been employed in the context of lightning related discharges, and offers a simple and efficient alternative to previous conventional time domain calculations. 

Abstract The first observation of possible transient luminous events (TLEs) on Jupiter was reported recently. Whereas initiation of elves on Jupiter has been theoretically studied before, the possibility of sprite streamer inception on Jupiter has not been investigated yet. Here we critically review the literature concerned with TLEs on Jupiter. Subsequently, we report on development of a numerical model for modeling of magnetized streamers in presence of Jupiter's strong magnetic field. The model utilizes the knowledge provided by recent observations of Jupiter's lightning and magnetic field by the Juno spacecraft. It is demonstrated that sprite streamer inception under realistic atmospheric conditions on Jupiter is possible.