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We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges. ; This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257 and by the Spanish Ministry of Science and Innovation, MINECO under projects FIS2014-61774-EXP and ESP2015-69909-C5-2-R. ; Peer Reviewed

We investigate the emergence of space stems ahead of negative leaders. These are luminous spots that appear ahead of an advancing leader mediating the leader's stepped propagation. We show that space stems start as regions of locally depleted conductivity that form in the streamers of the corona around the leader. An attachment instability enhances the electric field leading to strongly inhomogeneous, bright, and locally warmer regions ahead of the leader that explain the existing observations. Since the attachment instability is only triggered by fields above 10 kV/cm and internal electric fields are lower in positive than in negative streamers, our results explain why, although common in negative leaders, space stems, and stepping are hardly observed if not absent in positive leaders. Further work is required to fully explain the streamer to leader transition, which requires an electric current persisting for timescales longer than the typical attachment time of electrons, around 100 ns.©2019. The Authors. ; This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257. A. Malagon-Romero and A. Luque acknowledge financial support from the State Agency for Research of the Spanish MCIU through the >Center of Excellence Severo Ochoa> award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709) ; Peer Reviewed

At high pressure electric discharges typically grow as thin, elongated filaments. In a numerical simulation this large aspect ratio should ideally translate into a narrow, cylindrical computational domain that envelops the discharge as closely as possible. However, the development of the discharge is driven by electrostatic interactions and, if the computational domain is not wide enough, the boundary conditions imposed to the electrostatic potential on the external boundary have a strong effect on the discharge. Most numerical codes circumvent this problem by either using a wide computational domain or by calculating the boundary conditions by integrating the Green's function of an infinite domain. Here we describe an accurate and efficient method to impose free boundary conditions in the radial direction for an elongated electric discharge. To facilitate the use of our method we provide a sample implementation. Finally, we apply the method to solve Poisson's equation in cylindrical coordinates with free boundary conditions in both radial and longitudinal directions. This case is of particular interest for the initial stages of discharges in long gaps or natural discharges in the atmosphere, where it is not practical to extend the simulation volume to be bounded by two electrodes. Program summary: Program Title: poisson_sparse_fft.py Program Files doi: http://dx.doi.org/10.17632/x7f6czrnsh.1 Licensing provisions: CC By 4.0 Programming language: Python Nature of problem: Electric discharges are typically elongated and their optimal computational domain has a large aspect ratio. However, the electrostatic interactions within the discharge volume may be affected by the boundary conditions imposed to the Poisson equation. Computing these boundary conditions using a direct integration of Green's function involves either heavy computations or a loss of accuracy. Solution method: We use a Domain Decomposition Method to efficiently impose free boundary conditions to the Poisson equation. This code provides a stand-alone example implementation. © 2018 The Author(s) ; This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257 ; Peer reviewed

Depression in old age deserves special attention in view of the fact of progressive population ageing, because of the way in which depression and risk factors interact in this period of life and the particularly negative impact of late-life depression on health and quality of life. This editorial aims to provide some insight into longitudinal aspects of depression in old age. Depression may follow varying trajectories (e.g. episode emergence, recurrence) across the lifespan. Late-life depression is not an exception. A symptom-based approach is presented as an appropriate research method to study the predictors and course of affective syndromes in old age. Findings from our studies on depressive symptom trajectories in old age revealed that participants with a course of unremitting elevated symptoms showed the highest levels of loneliness across the trajectory groups and that participants with subclinical symptoms also showed higher levels of loneliness than their counterparts with a minimal-symptom course trajectory. This highlights the need to address loneliness as a way of dealing with depression in old age. ; This work was supported by the 5-year Ageing Trajectories of Health: Longitudinal Opportunities and Synergies (ATHLOS) project. The ATHLOS project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 635316; Instituto de Salud Carlos III-FIS under grant number PI16/00218; and Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM).

Halos and elves are transient luminous events produced in the lower ionosphere as a consequence of lightning-driven electromagnetic fields. These events can influence the upper atmospheric chemistry and produce optical emissions. We have developed different two-dimensional self-consistent models that couple electrodynamical equations with a chemical scheme to simulate halos and elves produced by vertical cloud-to-ground lightning discharges, compact intracloud discharges and energetic in-cloud pulses. The optical emissions from radiative relaxation of excited states of molecular and atomic nitrogen and oxygen have been calculated. We have upgraded previous local models of halos and elves to calculate for the first time the vibrationally detailed optical spectra of elves triggered by compact intracloud discharges and energetic in-cloud pulses. According to our results, the optical spectra of elves do not depend on the type of parent lightning discharge. Finally, we have quantified the local chemical impact in the upper atmosphere of single halos and elves. In the case of the halo, we follow the cascade of chemical reactions triggered by the lightning-produced electric field during a long-time simulation of up to 1 s. We obtain a production rate of NO molecules by single halos and elves of 10 and 10 molecules/J, respectively. The results of these local models have been used to estimate the global production of NO by halos and elves in the upper atmosphere at ∼10 Tg N/year. This global chemical impact of halos and elves is 7 orders of magnitude below the production of NO in the troposphere by lightning discharges. ©2018. American Geophysical Union. All Rights Reserved. ; This work was supported by the Spanish Ministry of Science and Innovation, MINECO, under projects ESP2015-69909-C5-2-R and ESP2017-86263-C4-4-R and by the EU through the H2020 Science and Innovation with Thunderstorms (SAINT) project (Ref. 722337) and the FEDER program. F.J.P.I. acknowledges a PhD research contract, code BES-2014-069567. A.L. was supported by the European Research Council (ERC) under the European Union's H2020 program/ERC grant agreement 681257. The simulation data and plot codes presented here are available from figshare repository at https://figshare.com/s/f1c9f6c7 bc728d6669dd. Alternatively, requests for the data and codes used to generate or displayed in figures, graphs, plots, or tables are also available after a request is made to the authors F.J.P.I. (fjpi@iaa.es), A. L. (aluque@iaa.es), or F. J. G.V. (vazquez@iaa.es).

Halos and elves are transient luminous events produced in the lower ionosphere as a consequence of lightning-driven electromagnetic fields. These events can influence the upper atmospheric chemistry and produce optical emissions. We have developed different two-dimensional self-consistent models that couple electrodynamical equations with a chemical scheme to simulate halos and elves produced by vertical cloud-to-ground lightning discharges, compact intracloud discharges and energetic in-cloud pulses. The optical emissions from radiative relaxation of excited states of molecular and atomic nitrogen and oxygen have been calculated. We have upgraded previous local models of halos and elves to calculate for the first time the vibrationally detailed optical spectra of elves triggered by compact intracloud discharges and energetic in-cloud pulses. According to our results, the optical spectra of elves do not depend on the type of parent lightning discharge. Finally, we have quantified the local chemical impact in the upper atmosphere of single halos and elves. In the case of the halo, we follow the cascade of chemical reactions triggered by the lightning-produced electric field during a long-time simulation of up to 1 s. We obtain a production rate of NO molecules by single halos and elves of 10 and 10 molecules/J, respectively. The results of these local models have been used to estimate the global production of NO by halos and elves in the upper atmosphere at ∼10 Tg N/year. This global chemical impact of halos and elves is 7 orders of magnitude below the production of NO in the troposphere by lightning discharges. ©2018. American Geophysical Union. All Rights Reserved. ; This work was supported by the Spanish Ministry of Science and Innovation, MINECO, under projects ESP2015-69909-C5-2-R and ESP2017-86263-C4-4-R and by the EU through the H2020 Science and Innovation with Thunderstorms (SAINT) project (Ref. 722337) and the FEDER program. F.J.P.I. acknowledges a PhD research contract, code BES-2014-069567. A.L. was supported by the European Research Council (ERC) under the European Union's H2020 program/ERC grant agreement 681257. The simulation data and plot codes presented here are available from figshare repository at https://figshare.com/s/f1c9f6c7 bc728d6669dd. Alternatively, requests for the data and codes used to generate or displayed in figures, graphs, plots, or tables are also available after a request is made to the authors F.J.P.I. (fjpi@iaa.es), A. L. (aluque@iaa.es), or F. J. G.V. (vazquez@iaa.es).

While lightning activity in Venus is still controversial, its existence in Jupiter and Saturn was first detected by the Voyager missions and later on confirmed by Cassini and New Horizons optical recordings in the case of Jupiter, and recently by Cassini on Saturn in 2009. Based on a recently developed 3-D model, we investigate the influence of lightning-emitted electromagnetic pulses on the upper atmosphere of Venus, Saturn, and Jupiter. We explore how different lightning properties such as total energy released and orientation (vertical, horizontal, and oblique) can produce mesospheric transient optical emissions of different shapes, sizes, and intensities. Moreover, we show that the relatively strong background magnetic field of Saturn can enhance the lightning-induced quasi-electrostatic and inductive electric field components above 1000 km of altitude producing stronger transient optical emissions that could be detected from orbital probes.©2017. American Geophysical Union. All Rights Reserved. ; This work was supported by the Spanish Ministry of Science and Innovation, MINECO under projects ESP2013-48032-C5-5-R, ESP2015-69909-C5-2-R, and FIS2014-61774-EXP and by the EU through the FEDER program. F.J.P.I. acknowledges a PhD research contract, code BES-2014-069567. A.L. was supported by the European Research Council (ERC) under the European Union's H2020 programme/ERC grant agreement 681257. ; Peer Reviewed

We investigate the attenuation of whistler waves generated by hypotetical Venusian lightning occurring at the altitude of the cloud layer under different ionospheric conditions. We use the Stanford full-wave method for stratified media of Lehtinen and Inan (2008) to model wave propagation through the ionosphere of Venus. This method calculates the electromagnetic field created by an arbitrary source in a plane-stratified medium (i.e., uniform in the horizontal direction). We see that the existence of holes in electronic densities and the magnetic field configuration caused by solar wind play an important role in the propagation of electromagnetic waves through the Venusian ionosphere. ©2017. American Geophysical Union. All Rights Reserved. ; This work was supported by the Spanish Ministry of Science and Innovation, Ministerio de Economia y Competitividad (MINECO) under projects ESP2015-69909-C5-2-R and FIS2014-61774-EXP, by the Research Council of Norway under contracts 208028/F50, 216872/F50, and 223252/F50 (CoE), and by the EU through the FEDER program. F. J. P. I. acknowledges a PhD research contract, code BES-2014-069567. N. L. was supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 320839. A. L. was supported by the European Research Council (ERC) under the European Union's H2020 program/ERC grant agreement 681257. ; Peer reviewed

This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. ; In this paper, a full-wave two-dimensional Finite-Difference-Time-Domain model is developed to evaluate the propagation effects of lightning electromagnetic fields over mountainous terrain in the Earth-ionosphere waveguide. In the model, we investigate the effect of the Earth-ionosphere waveguide structure and medium parameters, including the effect of the ionospheric cold plasma characteristics, the effect of the Earth curvature, and the propagation effects over mountainous terrain. For the first time, the obtained results are validated against simultaneous experimental data consisting of lightning currents measured at the Säntis Tower and electric fields measured in Neudorf, Austria, located at 380-km distance from the tower. It is shown that both the time delays and amplitudes of the lightning electromagnetic fields at 380-km distance can be strongly affected by the ionospheric electron density profile, the mountainous terrain, and the Earth curvature. After taking into account the effect of the irregular terrain between the Säntis Tower and the field measurement station, the vertical electric fields calculated by using our model are found to be in good agreement with the corresponding measured cases occurred in both daytime and nighttime. The ideal approximation used in either the classical solutions or the simplified models might lead to inaccuracies in the estimated reflection height. Furthermore, we discuss the sensitivity of our results by considering different return stroke models, as well as different typical values of the return stroke speed and of the ground conductivity. © 2019. The Authors. ; This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC Grant Agreement 681257 and Swiss National Science Foundation under Project 200021_147058. ; Peer reviewed

The emerging field of high energy atmospheric physics (HEAP) includes terrestrial gamma-ray flashes, electron-positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires appropriate models for the interaction of electrons, positrons and photons of up to 40MeV energy with atmospheric air. In this paper, we benchmark the performance of the Monte Carlo codes Geant4, EGS5 and FLUKA developed in other fields of physics and of the custom-made codes GRRR and MC-PEPTITA against each other within the parameter regime relevant for high energy atmospheric physics. We focus on basic tests, namely on the evolution of monoenergetic and directed beams of electrons, positrons and photons with kinetic energies between 100keV and 40MeV through homogeneous air in the absence of electric and magnetic fields, using a low energy cutoff of 50keV. We discuss important differences between the results of the different codes and provide plausible explanations. We also test the computational performance of the codes. The Supplement contains all results, providing a first benchmark for present and future custom-made codes that are more flexible in including electrodynamic interactions. ; Alexander Broberg Skeltved is supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 320839 and the Research Council of Norway under contracts 208028/F50, 216872/F50, and 223252/F50 (CoE). Alejandro Luque was supported by the European Research Council (ERC) under the European Union's H2020 programme/ERC grant agreement 681257 and by the Spanish Ministry of Economy and Competitiveness, MINECO under projects ESP2013-48032-C5-5-R and FIS2014-61774-EXP that include EU funding through the FEDER program. Gabriel Diniz is financial supported by the Brazilian agencies CAPES and CNPq. ; Peer Reviewed

We present the main parameters, design features, and optical characterization of the Granada Sprite Spectrograph and Polarimeter (GRASSP), a ground- based spectrographic system intended for the analysis of the spectroscopic signature of transient luminous events (TLEs) occurring in the mesosphere of the Earth. It has been designed to measure the spectra of the light emitted from TLEs with a mean spectral resolution of 0.235 nm and 0.07 nm/px dispersion in the wavelength range between 700 and 800 nm. (C) 2016 Optical Society of America ; Spanish Ministry of Science and Innovation, Ministerio de Economia y Competitividad (MINECO) (ESP2013-48032-C5-5-R, ESP2015-69909-C5-2-R, FIS2014-61774-EXP); European Union FEDER Program; Ramon y Cajal Contract (RYC-2011-07801). ; Peer reviewed

This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.https://creativecommons.org/licenses/by-nc-nd/4.0/ ; We investigate the launch of negative upward streamers from sprite glows. This phenomenon is readily observed in high-speed observations of sprites and underlies the classification of sprites into carrot or column types. First, we describe how an attachment instability leads to a sharply defined region in the upper part of the streamer channel. This region has an enhanced electric field, low conductivity and strongly emits in the first positive system of molecular nitrogen. We identify it as the sprite glow. We then show how, in the most common configuration of a carrot sprite, several upward streamers emerge close to the lower boundary of the glow, where negative charge gets trapped and the lateral electric field is high enough. These streamers cut off the current flowing toward the glow and lead to the optical deactivation of the glow above. Finally, we discuss how our results naturally explain angel sprites. ©2019. The Authors. ; Information on how to access the code used to run the simulations as well as the output data analyzed in this study is available in the supporting information. This work was supported by the European Research Council (ERC) under the European Union H2020 program/ERC Grant Agreement 681257. A. Malagon Romero and A. Luque acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" Award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). J. Teunissen was supported by postdoctoral fellowship 12Q6117N from Research Foundation-Flanders (FWO). The aircraft observations were sponsored by the Japanese National Broadcasting System, NHK. H. C. Stenbaek-Nielsen and M. G. McHarg were supported by Grants 1104441 and 1201683 from the U.S. National Science Foundation to the University of Alaska Fairbanks and the U.S. Air Force Academy, respectively. The simulation code used for this work is available at this site (https://gitlab.com/MD-CWI-NL/afivo-streamer).The version used for the simulations corresponds to the commit a3e2241fba 15f177b26e79106cef7354cbe09d68. Configuration files as well as the output data are available at this site (https://doi.org/10.5281/zenodo.3478177). ; Peer reviewed

©2020. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.https://creativecommons.org/licenses/by-nc/4.0/ ; Narrow bipolar events (NBEs) (also called narrow bipolar pulses [NBPs] or compact intracloud discharges [CIDs]) are energetic intracloud discharges characterized by narrow bipolar electromagnetic waveforms identified from ground-based very low frequency (VLF)/low-frequency (LF) observations. The simplified ray-theory method proposed by Smith et al. (1999, https://doi.org/10.1029/1998JD200045; 2004, https://doi.org/10.1029/2002RS002790) is widely used to infer the altitude of intracloud lightning and the effective (or virtual) reflection height of the ionosphere from VLF/LF signals. However, due to the large amount of high-frequency components in NBEs, the propagation effect of the electromagnetic fields for NBEs at large distance depends nontrivially on the geometry and the effective conductivity of the Earth-ionosphere waveguide (EIWG). In this study, we investigate the propagation of NBEs by using a full-wave Finite-Difference Time-Domain (FDTD) approach. The simulated results are compared with ground-based measurements at different distances in Southern China, and we assess the accuracy of the simplified ray-theory method in estimating the altitude of the NBE source and the effective reflection height of the ionosphere. It is noted that the evaluated NBE altitudes have a slight difference of about ±1 km when compared with the full-wave FDTD results, while the evaluated ionospheric reflection heights are found to be bigger than those obtained from FDTD model by about 5 km. ©2020. The Authors. ; This work was supported by the European Research Council (ERC) under the European Union H2020 Programme/ERC Grant 681257. The ground-based VLF/LF measurements related to this article can be obtained from CAS Key Laboratory of Geo-space Environment in the School of Earth and Space Sciences at University of Science and Technology of China in Hefei, China (http://222.195.83.28/) ; Peer reviewed

Trabajo presentado en el III Spanish Symposium on Physiology and Breeding of Cereals (III Simposio Español de Fisiología y Mejora de Cereales), celebrado online el 17 y 18 de noviembre de 2020. ; Drought tolerance is a complex phenomenon comprising many physiological, biochemical and morphological changes at both aerial and below ground levels. In this work, we explore the strategy of two oat cultivars to cope with drought, over an imposed water deficit time course of 20 days, based on root morphological, anatomical, physiological and molecular studies. We observed that the susceptible genotype increased dramatically the abscisic acid, at a relative soil water content as high as 60% resulting in a reduction of stomatal conductance. Despite this, leaf water potential decreased simultaneously due to a decrease in root hydraulic conductivity (conductivity per root length) in this genotype that showed early drought symptoms. By contrast, the resistant genotype, showed a mild and slow increase in abscisic acid that allowed maintaining transpiration longer. This was associated with an increase in root hydraulic conductivity together with root architectural changes such as an increase in total root length and in the length of the thinnest roots. In addition, root anatomical changes facilitated hydraulic transport and a reduction of metabolic cost. This strategy allowed the resistance genotype to maintain higher water potential reducing drought symptoms and promoting growth under water deficit conditions. ; This work was supported by the Spanish Ministry of Science and Innovation [PID2019-104518RB-I00], and regional government through the AGR-253 group.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. ; The physical mechanism of Narrow bipolar events (NBEs) has been studied for decades but it still holds many mysteries. Recent observations indicate that the fast breakdown discharges that produce NBEs sometimes contain a secondary fast breakdown that propagates back in the opposite direction but this has not been fully addressed so far in electromagnetic models. In this study, we investigate fast breakdown using different approaches that employ a Modified Transmission Line with Exponential decay (MTLE) model and propose a new model, named "rebounding MTLE model," which reproduces the secondary fast breakdown current in NBEs. The model provides new insights into the physics of the fast breakdown mechanism. © 2022 The Authors. ; This work was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257. Additionally, this work was supported by the Spanish Ministry of Science and Innovation, MINECO, under project PID2019-109269RB-C43 and FEDER program. Dongshuai Li, Alejandro Luque, and F. J. Gordillo-Vázquez acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). ; Peer reviewed