A domain-decomposition method to implement electrostatic free boundary conditions in the radial direction for electric discharges

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 for electric discharges 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 for an elongated electric discharge. To facilitate the use of our method we provide a sample implementation.Comment: 21 pages, 4 figures, a movie and a sample code in python. A new Appendix has been adde

Gobal and regional chemical influence of sprites: Reconciling modeling results and measurements

Mesospheric electrical discharges, known as sprites, formed by fast-propagating streamers, have been shown to create localized enhancements of atmospheric constituents such as N, O, NOx, N2O, and HOx, as indicated by both, modeling results and space-based measurements. In this study, we incorporate the occurrence rate of sprites into a chemistry-climate model using meteorological parameters as a proxy. Additionally, we introduce the injection of chemical species by sprites into the model, based on electrodynamical modeling of individual sprite streamers and observations from space. Our modeling results show a good agreement between the simulated sprite distribution and observed data on a global scale. While the global influence of sprites on the atmospheric chemistry is found to be negligible, our findings reveal their measurable chemical influence at regional scale, particularly for the concentration of HNO3 and HNO4 within the mesosphere. The simulations also suggest that sprites could be responsible for the observed NO2 anomalies at an altitude of 52 km above thunderstorms, as reported by MIPAS. Finally, a projected simulation reveals that the occurrence rate of sprites could increase at a rate of 14 % per 1 K rise in the global temperature

On the emergence mechanism of carrot sprites

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

A plasma fatty acid profile associated to type 2 diabetes development: from the CORDIOPREV study

Purpose: The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide. For this reason, it is essential to identify biomarkers for the early detection of T2DM risk and/or for a better prognosis of T2DM. We aimed to identify a plasma fatty acid (FA) profile associated with T2DM development. Methods: We included 462 coronary heart disease patients from the CORDIOPREV study without T2DM at baseline. Of these, 107 patients developed T2DM according to the American Diabetes Association (ADA) diagnosis criteria after a median follow-up of 60 months. We performed a random classification of patients in a training set, used to build a FA Score, and a Validation set, in which we tested the FA Score. Results: FA selection with the highest prediction power was performed by random survival forest in the Training set, which yielded 4 out of the 24 FA: myristic, petroselinic, α-linolenic and arachidonic acids. We built a FA Score with the selected FA and observed that patients with a higher score presented a greater risk of T2DM development, with an HR of 3.15 (95% CI 2.04–3.37) in the Training set, and an HR of 2.14 (95% CI 1.50–2.84) in the Validation set, per standard deviation (SD) increase. Moreover, patients with a higher FA Score presented lower insulin sensitivity and higher hepatic insulin resistance (p < 0.05). Conclusión: Our results suggest that a detrimental FA plasma profile precedes the development of T2DM in patients with coronary heart disease, and that this FA profile can, therefore, be used as a predictive biomarker

Numerical investigation on the advance of leader channels in lightning and long sparks

This thesis aims to study the stepped propagation of lightning channels with a prominently numerical approach. We have built a self-consistent state-ofthe- art 2D cylindrically symmetric model that accounts for charge transport, electrostatic interactions, gas heating, and expansion. In our efforts for improving our model, we have implemented a numerical method to solve the Poisson equation that allows us to reduce the size of the computational domain, speeding up our simulations. This method is also valid to optimize the calculation of the photoionization term in streamer discharge codes. We have used our model to investigate the emergence of space stems. 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. Space stems are known to readily launch counter-propagating streamers. These are believed to heat the space stem close to leader temperatures. Similarly, high-altitude electric discharges such as sprites develop a non-thermal version of a space stem known as glow. As space stems, glows also shoot counterpropagating streamers. We have studied the mechanism underlying the onset of these counter-propagating streamers with the AFIVO 3D streamer model. Our results show that an attachment instability leads to a charge accumulation at the boundaries of the glow, which enables it to shoot these counterpropagating streamers. This explains the characteristic shape of carrot sprites. Finally, we have studied the effect of a forced electric current through a spacestem- like structure. The source of this electric current could be the counterpropagating streamers mentioned above. In the same way, we have studied the influence of water in the development of a space stem under such conditions. Our results show that water enhances the initially small plasma inhomogeneities. This explains some of the features observed in the leader stepping and highlights the relevance of water chemistry models to address leader propagation.Esta tesis tiene por objeto estudiar la propagación a saltos del canal de un rayo con un enfoque eminentemente numérico. Hemos desarrollado nuevo modelo numérico 2D con simetría cilíndrica capaz de describir el transporte de carga, las interacciones electrostáticas, el calentamiento y la expansión del gas que se dan en una descarga eléctrica. Al desarrollar un modelo numérico, es siempre importante su optimización para así agilizar las simulaciones. Para ello hemos implementado un método numérico que nos permite resolver la ecuación de Poisson en un dominio computacional ajustado a las dimensiones físicas de la descarga que simulamos. Este método también se puede utilizar para optimizar el cálculo del término de fotoionización que aparece en los códigos numéricos de descargas tipo dardo. Hemos usado nuestro modelo para investigar el origen de los tallos espaciales. Estos son manchas luminosas que aparecen delante de un líder a medida que se propaga. Nuestros resultados muestran que los tallos espaciales se originan en zonas de conductividad reducida en los dardos que forman las coronas en torno al líder. Una inestabilidad de adhesión incrementa el campo eléctrico en estas zonas de conductividad reducida. Esto conduce a zonas inhomogéneas, brillantes y más calientes delante del líder que explican las observaciones existentes. Los tallos espaciales son capaces de lanzar descargas tipo dardo. Estas descargas podrían ser responsables de calentar el tallo espacial hasta temperaturas cercanas a las del líder. De igual manera, descargas eléctricas a gran altitud como los ”sprites” desarrollan una versión a temperatura ambiente del tallo espacial que se conoce como ”brillo”. Como los tallos espaciales, los brillos son capaces de lanzar dardos. Hemos estudiado el mecanismo que subyace al lanzamiento de estos dardos con AFIVO 3D, un modelo para descargas eléctricas de tipo dardo. Nuestros resultados apuntan a que, de nuevo, una inestabilidad de adhesión produce una acumulación de carga en los bordes del ”brillo”, lo que lleva al lanzamiento de descargas tipo dardo. Esto explica la característica forma de los ”sprites” de tipo zanahoria. Finalmente, hemos estudiado el efecto que tiene una corriente fluyendo a través de un plasma similar al tallo espacial. El origen de esta corriente podría ser las descargas tipo dardo que emanan del mismo. También hemos estudiado la influencia del agua en el desarrollo del tallo espacial bajo una corriente eléctrica forzada. Nuestros resultados muestran que el agua favorece el desarrollo de inhomogeneidades en el plasma que inicialmente eran pequeñas. Esto explica algunas de las características observadas en los saltos de los lideres y subraya la importancia de que los modelos químicos incluyan agua para abordar la propagación del líder.Tesis Univ. Granada.European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257State 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

Streamer propagation in humid air

We investigate the effect of humidity on the propagation of streamers in air. We present a minimal set of chemical reactions that takes into account the presence of water in a nonthermal air plasma and considers ionization, attachment, detachment, recombination and ion conversion including water cluster formation. We find differences in streamer propagation between dry and humid air that we attribute mostly to an enhanced effective attachment rate in humid air, leading to higher breakdown electric field and threshold field for propagation. This higher effective attachment rate in humid conditions leads to a faster decay of the conductivity in the streamer channel, which hinders the accumulation of charge in the streamer head. In some cases a propagating streamer solution still exists at the expense of a smaller radius and lower velocity. In other cases a high humidity leads to the stagnation of the streamer. We finally discuss how all these statements may affect streamer branching and the dimensions and lifetime of a streamer corona. © 2022 IOP Publishing Ltd.This work was supported by Junta de Andalucía under the Project PY20-00831. A Malagón-Romero acknowledges a postdoctoral contract under the Project PY20-00831. A Malagón Romero and A Luque acknowledge 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). The simulation code for this work is available at https://gitlab.com/MD-CWI-NL/afivo-streamer. The version used for the simulations corresponds to the commit 1ff2676ba48a5eb568f06c7b11a548629a5ff20c. All the simulations were carried out in the MareNostrum Supercomputer under Project Number FI-2021-2-0025, granted by the Barcelona Supercomputing Center.Peer reviewe

Spontaneous Emergence of Space Stems Ahead of Negative Leaders in Lightning and Long Sparks

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 Reviewe

Editorial for the Special Issue &ldquo;Advances in Atmospheric Electricity&rdquo;

The field of atmospheric electricity has been very active in the last decades [...

Analysis of the spatial nonuniformity of the electric field in spectroscopic diagnostic methods of atmospheric electricity phenomena

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.The spatial nonuniformity of the electric field in air discharges, such as streamers, can influence the accuracy of spectroscopic diagnostic methods and hence the estimation of the peak electric field. In this work, we use a self-consistent streamer discharge model to investigate the spatial nonuniformity in streamer heads and streamer glows. We focus our analysis on air discharges at atmospheric pressure and at the low pressure of the mesosphere. This approach is useful to investigate the spatial nonuniformity of laboratory discharges as well as sprite streamers and blue jet streamers, two types of transient luminous events taking place above thunderclouds. This characterization of the spatial nonuniformity of the electric field in air discharges allows us to develop two different spectroscopic diagnostic methods to estimate the peak electric field in cold plasmas. The commonly employed method to derive the peak electric field in streamer heads underestimates the electric field by about 40–50% as a consequence of the high spatial nonuniformity of the electric field. Our diagnostic methods reduce this underestimation to about 10–20%. However, our methods are less accurate than previous methods for streamer glows, where the electric field is uniformly distributed in space. Finally, we apply our diagnostic methods to the measured optical signals in the second positive system of N2 and the first negative system of N+ 2 of sprites recorded by Armstrong et al. (1998, https://doi.org/10.1016/S1364-6826(98)00026-1) during the SPRITE's 1995 and 1996 campaigns. ©2019. The Authors.This work was supported by the Spanish Ministry of Science and Innovation, MINECO under project ESP2017-86263-C4-4-R and by the EU through the European Research Council (ERC) under the European Union's H2020 programm/ERC grant agreement 681257. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement SAINT 722337. The authors 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). F. J. P. I. acknowledges a PhD research contract, code BES-2014-069567Peer reviewe

Global and regional chemical influence of sprites: reconciling modelling results and measurements

Mesospheric electrical discharges, known as sprites and formed by fast-propagating streamers, have been shown to create localized enhancements of atmospheric constituents such as N, O, NOx, N2O, and HOx, as indicated by both modelling results and space-based measurements. In this study, we incorporate the occurrence rate of sprites into a chemistry–climate model using meteorological parameters as a proxy. Additionally, we introduce the injection of chemical species by sprites into the model based on electrodynamical modelling of individual sprite streamers and observations from space. Our modelling results show a good agreement between the simulated sprite distribution and observed data on a global scale. While the global influence of sprites on the atmospheric chemistry is found to be negligible, our findings reveal their measurable chemical influence at the regional scale, particularly for the concentration of HNO3 and HNO4 within the mesosphere. The simulations also suggest that sprites could be responsible for the observed NO2 anomalies at an altitude of 52 km above thunderstorms, as reported by MIPAS. Finally, a projected simulation reveals that the occurrence rate of sprites could increase at a rate of 14 % per 1 K rise in the global temperature