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have forced the definition of a new type of spicule, "type II's", that are characterized by rising rapidly, having short lives, and by fading away at the end of their lifetimes. Here, we report on features found in realistic 3D simulations of the outer solar atmosphere that resemble the observed type II spicules. These features evolve naturally from the simulations as a consequence of the magnetohydrodynamical evolution of the model atmosphere. The simulations span from the upper layer of the convection zone to the lower corona and include the emergence of horizontal magnetic flux. The state-of-art Oslo Staggered Code (OSC) is used to solve the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field lines. We describe in detail the physics involved in a process which we consider a possible candidate as a driver mechanism to produce type II spicules. The modeled spicule is composed of material rapidly ejected from the chromosphere that rises into the corona while being heated. Its source lies in a region with large field gradients and intense electric currents, which lead to a strong Lorentz force that squeezes the chromospheric material, resulting in a vertical pressure gradient that propels the spicule along the magnetic field, as well as Joule heating, which heats the the jet material, forcing it to fade., 31 pages, 9 figures, Accepted in ApJ

Esta tesis doctoral ha sido realizada con datos y resultados obtenidos en el Centro de Investigación Atmosférica de Izaña de la Agencia Estatal de Meteorología, donde el doctorando desarrolló su trabajo como funcionario de carrera del Cuerpo Superior de Meteorólogos del Estado, y su director principal de tesis trabaja como Director de dicho centro., Tesis Univ. Granada. Programa Oficial de Doctorado en Física y Ciencias del Espacio, This work was funded by the Norwegian Research Council project GAME (Causes and effects of Global and Arctic changes in the Methane budget), grant no. 207587, under the program NORKLIMA, and the EU project ACCESS (Arctic Climate Change Economy and Society). ACCESS received funding from the European Union under grant agreement no. 265863 within the Ocean of Tomorrow call of the European Commission Seventh Framework Programme, This study was developed within the Global Atmospheric Watch (GAW) Programme at the Izaña Atmospheric Research Center, financed by AEMET, WMO SDS-WAS Regional Centre for Northern Africa, Middle East and Europe, held by AEMET and BSC-CNS, The University of Granada (Spain) and its “Physics and Space Sciences” PhD Programme are acknowledged by A. J. Gómez-Peláez and E. Cuevas. AEROATLAN project (CGL2015-17 66229-P), co-funded by the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund contributed to this study

The complexity of many of the processes that take place in the solar atmosphere and interior has led to the development of large, often multidimensional, numerical models to understand in detail the underlying physics. The study of phenomena from jets, surges and spicules, all the way to coronal mass ejections (CME´s) or solar flares, of structures such as coronal arcs or of processes such as convection or wave propagation, requires combining aspects of hydrodynamics, electromagnetism, plasma physics and radiative transport. The development of numerical codes allows to solve in detail the equations of those fields together. One of the basic aspects of these numerical codes is the equation of state (EOS) that they implement. The EOS can be very simple, or very complex, depending on the degree of realism needed to obtain relevant results. A code at the forefront of the study of dynamical processes in the solar atmosphere is the Bifrost code, developed at the University of Oslo. The fundamental EOS implemented in Bifrost deals with an ideal gas with ionization/recombination and molecular formation/dissociation processes; it is realistic and complex, and contains detailed microphysics. In this Graduation Thesis, we study the Bifrost EOS from a double perspective: on the one hand, we carry out a detailed characterization of the EOS, covering a large variety of aspects of the thermodynamics of partially ionized gases; on the other hand, we study the shock transitions, in particular the Hugoniot curves, allowed by the EOS. Concerning the first aspect, the motivation to carry out the characterization is that the Bifrost EOS is not well documented in the literature, which may constitute a problem for users of the code. Concerning the second, one cannot find publications that describe the general behavior of shocks calculated with this EOS. Given the ionization/recombination and molecular formation/dissociation processes taking place in the solar atmosphere and included in the EOS, this study can be important to understand the properties of shocks in the numerical models. In the first part, the characterization of the EOS is carried out by calculating thermodynamic quantities on the basis of the tables of temperature and pressure as a function of density and internal energy obtained from the EOS. For all the numerical calculations throughout this work original Python programs have been developed independently of Bifrost’s own program suite. To begin with, quantities that do not require advanced numerical methods, such as atomic mass per particle or specific heat at constant volume, are determined. Next, we calculate more advanced quantities, such as the entropy distribution, ionization or dissociation coefficients, the Chandrasekhar adiabatic coefficients, the adiabatic gradient, the specific heat ratio γ, and the speed of sound, most of which require high-order integrations or interpolations in one or two dimensions. The results are compared to those obtained for the equation of state for the simplest ideal gases, i.e., those with no changes in chemical composition, showing the importance of taking into account the ionization and molecular formation processes. In the case of entropy, the integration methods used are discussed, and the results compared with the adiabatic curves facilitated by Dr H Ludwig obtained in the context of the COBOLD code, thus verifying the validity of our results. Additionally, a detailed analytical expression for the internal energy of the gas is developed that includes all the ionization levels for Hydrogen and Helium and the formation of H2 molecules. The obtained formula is tested by making calculations in regions where the chemical composition does not vary, obtaining an excellent fit to the general curves obtained from the Bifrost EOS table in those regions. In this way, we now have at our disposal detailed information about the ionization or molecular formation processes for H and He that take place in the different ranges of density and internal energy (or pressure and temperature) in the solar atmosphere. In the second part of the work, the jumps of pressure, temperature and density across a shock, the corresponding increase in entropy and the incoming Mach numbers allowed by the Bifrost EOS are studied in detail. For this, the Rankine-Hugoniot jump relations are used and the corresponding Hugoniot curves are obtained, comparing the results to the well known ones for simple ideal gases. First, analytical expressions are derived for the jumps allowed when the component of the internal energy associated with ionization and molecular dissociation processes is uniform in the local thermodynamical domains where the pre-shock and post-shock states are located. This leads to unexpected results when that component has a different value before and after the shock transition. Also, an analytical expression for the derivative of post-shock pressure with respect to post-shock density along the Hugoniot curve is calculated in the general case. Then, a program is created to calculate Hugoniot and Mach number curves numerically for the general case. To illustrate the results, curves starting at pre-schock states in five regions of interest are calculated. Those curves have entry states located in regions of simple ideal gas, but are such that, along their path, cross bands of ionization or molecular dissociation. The crossing gives rise to striking consequences: the density jump can become much larger in those shocks than in the standard simple ideal gas ones; duplication in the admissible pressure and temperature jumps for a given density jump is also obtained. The temperature jump for a given pressure jump is much reduced compared to the simplest ideal gas case when the postshock state is in one of those bands, the reason being that the incoming energy in the shock may be used to ionize (or cause molecular dissociation in) the gas to a larger extent than in increasing its temperature. Summarizing, we have derived a large number of thermodynamical and shock-related properties of the gas described by the EOS of use in the Bifrost code exclusively on the basis of the temperature and pressure maps as functions of density and internal energy. The results illuminate the behavior of the gas in various regimes of interest for the calculations in the upper solar interior, photosphere, chromosphere, transition region and corona. Particularly interesting results are obtained concerning the properties of shocks. We expect that the current results can be of use to the community using the Bifrost code in future.

Introducción: desde hace ya más de diez años, los avances en la instrumentación astronómica, en particular en Física Solar, han permitido alcanzar muy alta resolución espacial en las observaciones fotosféricas, llegándose a obtener resolución mejor que 200 km. Ello ha permitido detectar la aparición de pequeñas estructuras magnéticas bipolares en el interior de gránulos en la superficie del Sol. Son varios los trabajos que hablan de este tipo de detecciones que sugieren que lo que se está viendo es la emergencia de un pequeño arco magnético desde el interior solar. Sin embargo, las observaciones no son suficientes para confirmar esta suposición ya que, incluso aplicando técnicas de inversión, sólo permiten obtener valores de variables físicas en el rango limitado de altura en que se forma la línea espectral observada y bajo suposiciones restrictivas. Es crucial utilizar modelado numérico tridimensional y localizar este tipo de estructuras en simulaciones magnetohidrodinámicas para conocer detalles estructurales, evolutivos y propiedades sobre las misma desde el interior solar hasta la atmósfera. Tres hitos históricos en la detección observacional de estas estructuras magnéticas han sido los siguientes: en el trabajo de De Pontieu (2002) se detectan por primera vez concentraciones de flujo magnético a escalas claramente subgranulares. Unos años más tarde, Centeno et al. (2007) detectan más detalles de estas concentraciones de campo magnético, encontrando una zona de campo horizontal en cuyos extremos se encuentran dos polos de campo magnético vertical de signo opuesto. Finalmente, en el trabajo de Martínez-González & Bellot (2009), se detectan de nuevo este tipo de estructuras pero un número suficientemente alto de veces como para poder realizar un estudio estadístico; estos autores también usaron líneas espectrales con formación a diferentes alturas y concluyeron que una fracción pequeña de las estructuras magnéticas ascendían desde la fotosfera hasta la cromosfera. Desde el punto de vista teórico solo ha habido un trabajo, realizado por Moreno-Insertis et al. (2017), en que, mediante modelado numérico 3D, se intenta entender la física de la formación, estructura y evolución de dichas concentraciones magnéticas de tamaño subgranular. Los autores detectan dos tipos diferentes de estas estructuras en un modelo radiativo-MHD realizado con el código Bifrost y para una situación de Sol en calma en que está teniendo lugar emergencia global de flujo magnético: estructuras de tubo magnético ascendente y estructuras de tipo capa. En el mismo trabajo, también se detectan capas magnéticas en otro modelo numérico 3D, de acceso público, también realizado con el código Bifrost, al que nos referiremos aquí con las siglas BPS. Nuestro objetivo en este TFM es completar este trabajo localizando estructuras magnéticas tubulares que emergen en el interior de gránulos en dicha simulación pública de Bifrost (BPS). Con esta detección probaremos que las micro-estructuras magnéticas tubulares también aparecen en modelos MHD con condiciones solares diferentes a las del modelo de Moreno-Insertis et al. (2017). La simulación BPS fue puesta a disposición de la comunidad científica a través del Hinode Data Center. Abarca desde las capas altas de la zona de convección hasta la corona solar, más concretamente desde 2.4 Mm por debajo de la superficie hasta 14.4 Mm por encima de ésta. La extensión horizontal del dominio es de 24×24 Mm2 . Estos datos contienen valores de temperatura, presión, densidad másica, densidad de partículas y las tres componentes del campo magnético y la velocidad. Los datos contituyen una secuencia temporal desde 3850s hasta 5410 s, aproximadamente media hora de tiempo solar, con cadencia de 10 segundos solares. Métodos: en primer lugar se ha realizado una caracterización de los datos de la simulación a través de las magnitudes velocidad y campo magnético. Se han representado mapas de color de uz y Bz a diferentes alturas con el fin de localizar en la BPS comportamientos y características similares a lo que conocemos del Sol observacional y/o teóricamente. También se ha llevado a cabo un análisis estadístico de estas magnitudes en las diferentes profundidades de la caja que corresponden a la zona de convección. Tras esto se ha procedido a la búsqueda del tipo de estructuras magnéticas mencionadas. Esta búsqueda se ha dividido en dos partes. Primero, se ha intentado localizar la emergencia de arcos magnéticos mediante una inspección a nivel superficial de mapas horizontales de velocidad vertical donde se han superpuesto isocontornos de intensidad de campo magnético. Esto se ha hecho con vistas a localizar fenómenos de aparición de estructuras bipolares. Para confirmar una detección se ha seguido la siguiente pauta: primeramente se ha exigido que apareciese una zona concentrada espacialmente de campo magnético horizontal en el interior del gránulo; después se requería que ese área aumentase 5 de intensidad y tamaño, apareciendo posteriormente dos polos de campo magnético vertical de signo mutuamente opuesto en los extremos de la zona cubierta por campo horizontal. Finalmente, hemos exigido que toda la estructura sea arrastrada hacia el intergránulo y que desaparezca allí. Sin embargo, la visualización de isocontornos no es una evidencia definitiva de la localización de arcos magnéticos ya que sólo vemos una sección horizontal y esto no es suficiente para conocer la forma de nuestra estructura magnética. Por esta razón, para la segunda parte del método de detección necesitamos visualización en 3D de los datos. Hemos usado el software VAPOR (UCAR) y, en particular, sus herramientas de cálculo de isosuperficies de diferentes variables físicas, de líneas de campo magnético, y de mapas de color sobre planos con orientación 3D arbitraria. Para visualizar las estructuras en tres dimensiones hemos calculado isosuperficies de intensidad de campo magnético para valores entre 100 y 200 G añadiendo mapas de velocidad vertical sobre planos horizontales. Se ha elegido un instante temporal en que la estructura haya evolucionado lo suficiente y se han podido descartar algunas de las candidatas de la visualización 2D por tener una forma irregular o por pertenecer a estructuras magnéticas intergranulares mayores. Para las estructuras que sí eran claramente tubos magnéticos, hemos visualizado toda su secuencia temporal para ver dónde se forman y cómo evolucionan. Para analizar las estructuras más a fondo hemos realizado dos pruebas más: una ha sido la representación de líneas de campo en el interior de tubo magnético para ver el comportamiento en el interior del objeto. Y una última que ha sido la representación de un mapa de intensidad de campo magnético en un plano trasversal a la estructura con el fin de conocer más información sobre el grado de concentración de la misma. Resultados: en la parte de caracterización de los datos hemos observado cómo la BPS reproduce características generales de la magnetoconvección que concuerdan con lo que conocemos observacional y/o teóricamente. En cuanto a la detección de estructuras magnéticas emergentes con forma de arco, hemos podido seleccionar hasta 26 estructuras mediante el método de detección 2D. Estas han sido tratadas como candidatas al tipo de estructura buscada a espera de la confirmación definitiva a través de la visualización 3D. Tras llevarla a cabo, confirmamos que 11 de las estructuras observadas se corresponden con el tipo de objeto buscado. En dichas estructuras se han observado una serie de características comunes. Primero, dado el proceso de selección escogido, siguen las pautas evolutivas ya descritas: emergencia en el interior del gr´anulo, arrastre hacia la región intergranular por los movimientos del plasma y desaparición de la estructura en el intergránulo; todo esto en un tiempo de vida próximo a los 5 minutos. También una serie de características estructurales: forma tubular plegada en forma de arco, identidad de tubo de flujo magnético en el sentido clásico electromagnético, independencia del resto de estructuras magnéticas del entorno y concentración notable con intensidades hasta 2 órdenes de magnitud por encima del entorno. En este trabajo se ilustran en detalle dos de dichas estructuras de tubo emergente. Una de ellas es un caso ejemplar que sigue los diferentes pasos evolutivos claramente. El otro es un caso especial donde la emergencia del arco magnético se ve sorprendida por la formación de un intergránulo bajo ella; esto pliega la estructura magnética y produce la emergencia de un doble arco. Los resultados obtenidos en este Trabajo Fin de Máster han sido usados como parte de una Letter publicada muy recientemente en Astrophysical Journal Letters (Moreno-Insertis et al., 2018). Introduction: for more than ten years now, the advances in astronomical instrumentation, in particular in solar physics, have allowed to reach high spatial resolution in photospheric observations, with details down to 0,2 00 now being routinely obtained. This led to the detection of the appearance of small bipolar magnetic structures within granules in the solar surface. Different research papers of the past and present decades have suggested that those small bipoles were indicative of the emergence of a tiny magnetic loop from the solar interior. However, the observations are not enough to confirm this conclusion: even after application of inversion techniques what one deduces is the distribution of physical variables in the limited height range where the observed spectral line is formed and under restrictive assumptions. It is necessary to carry out three-dimensional numerical modelling, locating this type of features in radiation-magnetohydrodynamic simulations, to be able to find out their origin, and their structural and evolutionary properties in the solar interior and atmosphere. Three milestones in the observational detection of this kind of magnetic structures were: De Pontieu (2002) identified a magnetic flux concentration on clearly subgranular scales for the first time. Some years later, Centeno et al. (2007) detected a suggestive evolutionary pattern whereby first a horizontal magnetic field patch appeared within a granule, with two vertical magnetic field patches of opposite polarity appearing on the edges of the horizontal field region at a later stage. Finally, Mart´ınezGonz´alez & Bellot (2009) detected a large number of instances of this kind of bipolar features so they could to make a statistical study. The authors used spectral lines forming at different heights and concluded that a small fraction of those magnetic structures rise above the photosphere, reaching the cromosphere. From the theoretical point of view, there is only one paper (Moreno-Insertis et al., 2017) in which the physics of the formation, configuration and evolution of subgranular magnetic concentrations is studied through three-dimensional numerical modelling. Those authors detected two kinds of such structures in a radiative-MHD model carried out with the Bifrost code for a quiet-Sun region with global emergence of magnetic flux: (a) rising magnetic flux tubes and (b) magnetic sheets coverning whole granules. They additionally detected the appearance of magnetic sheets in a different 3D simulation, also obtained with the Bifrost code but publicly available, called the Bifrost Public Simulation, or BPS, in the following. In this Master’s thesis we attempt to complete their work by finding rising tiny magnetic tubes emerging within granules in the BPS. This will be a first step toward proving the existence of this kind of magnetic structures in different solar environments. The BPS was made available to the scientific community through the Hinode Data Center. The model encompasses from the top layers of the convection zone to the corona, more precisely 2,4 Mm below and 14,4 Mm above the surface. The horizontal extent is 24 × 24 Mm2 . The data cubes contain values of temperature, gas pressure, density and the three components of velocity and magnetic field. The time sequence extends for 26 minutes of solar time with 10 s cadence. Method: first of all we have carried out a characterization of the BPS data using the magnetic field and velocity vector fields. We have drawn color maps of their vertical components at different heights to find similarities with the expectations from the theoretical and observational results of those heights. Additionally, we have carried out a brief statistical analysis of those quantities in the depths of the box corresponding to the convection zone. The actual search for the concentrated magnetic structures that is the main objective of this Master’s thesis was implemented in two successive stages. A first selection of candidates was attempted via inspection of maps of the vertical velocity at the solar surface with isocontours of the vertical and horizontal magnetic field components superimposed. The sites of emergence of bipolar regions were located by requesting that (1) a patch of horizontal field appears in the interior of a granule with area and magnetic strength growing in time; this was to be followed by (2) the appearance of two patches of vertical field of mutually opposite polarity; finally, (3) the whole structure had to be seen moving toward the intergranule, where it disappeared. In the second stage, more conclusive evidence for the presence of rising magnetic loops was sought via 3D visualization: the analysis of isocontours on horizontal surfaces cannot provide complete eviden3 ce since it misses the distribution of variables in the interior and atmosphere. For the 3D visualisation, the software VAPOR (UCAR) was used, specifically its tools to calculate isosurfaces of different physical variables, magnetic field lines and color maps in planes with arbitrary 3D orientation. In particular, we have used isosurfaces of magnetic field strength at B = 100-200 G, adding maps for the vertical component of the velocity on horizontal planes. Some of the cases selected in the previous (2D) stage had to be discarded given their irregular shape or their links with preexisting intergranular magnetic features. For those cases clearly identified as magnetic tubes we have studied a time sequence to check their origin and time evolution. For them, two further 3D tests were carried out: we have drawn field lines in them to have an impression of the associated magnetic surfaces. Second, we have plotted field intensity maps on transverse vertical planes to check the degree of concentration of the magnetic distribution. Results: regarding the characterization of the BPS, we have confirmed that the features explored match the general expectations from the theory of magnetoconvection. Concerning the detection of rising magnetic loops, we could isolate up to 26 cases of evolutionary patterns that fulfilled the conditions set using the 2D horizontal map method. After applying the more strict 3D methods, we could confirm 11 of them as concentrated rising magnetic loops. Corresponding to the requests set for a positive detection, those tubes emerge from the subphotospheric layers and become visible in the granular cell interior. They are then dragged toward the intergranule where they eventually disappear. The whole process takes an approximate average time of some five minutes. Some common features for those tubes are: magnetic isosurfaces with rising loop shape, magnetic field lines roughly contained within the isosurfaces, marked magnetic concentration with up to two orders of magnitude larger strength in the center of the loop structure than in the surrounding volume. This thesis focuses on, and illustrates in detail, two of the emerging concentrated magnetic tubes. One is a canonical case that clearly follows the general evolutionary pattern mentioned above. The other one is a special case in which the emergence of the magnetic loop is perturbed by the simultaneous formation of an intergranular lane in its domain. This causes a fold in the magnetic arch and the resulting emerging structure has the shape of a double loop. The results obtained in this Master’s thesis have been used as part of a Letter recently published in the Astrophysical Journal Letters (Moreno-Insertis et al., 2018).

A bewildering variety of eruptive and ejective phenomena continually take place in the solar atmosphere on a wide range of space and time scales. Particular attention was devoted in the past decades to those associated with the reconnection of magnetic field lines of separate plasma systems that come into contact in the atmosphere, especially when this is the result of the emergence of magnetic flux from the solar interior. Such events can cause a large disruption of the solar atmosphere, lead to the release of magnetic energy which is turned into kinetic and internal energy of the plasma and radiation, launch impulsive mass ejections, and bring about the reconfiguration of the magnetic domain structure in the chromosphere and corona. Even though observationally known for many decades now, among those dynamic phenomena there is one whose understanding has progressed very slowly: the surges. Surges are cool, dense and non-collimated ejections typically observed in chromospheric lines, like Hα 6563 Å, with velocities of a few to several tens of km s-1 and lengths of 10-50 Mm. They frequently arise in the solar atmosphere related to other transient events like UV bursts or EUV/X-Ray coronal jets. Through idealized numerical experiments, the surges have been explained as a by-product of magnetic reconnection taking place between emerging and preexisting magnetic systems in the atmosphere that eventually causes chromospheric plasma to be dragged into higher layers. In spite of their interest, those experiments miss a number of fundamental physical mechanisms at work when the surges are ejected, so they constitute only a preliminary step in this field. This thesis addresses the surge phenomenon under a fourfold perspective: (1) its basic approach is theoretical, and is carried out by modeling the formation and evolution of the surges using a radiation-magnetohydrodynamics (R-MHD) code that includes a realistic treatment of the material plasma properties and radiation transfer; (2) from an observational point of view, we analyze coordinated high-resolution observations of the chromosphere and transition region (TR), exploring the response of TR lines to a surge ejection and the close relationship of surges to other events like UV bursts; (3) from a forward modeling perspective, synthetic observations are created that permit us to understand some of the peculiar features seen in the actual observations and provide a theoretical basis for them; and (4) from the point of view of code development, we have created a Fortran module that improves the computational efficiency of the ambipolar diffusion term and opens up the possibility of including partial ionization effects on the electrodynamics of the system via the generalized Ohm's law. The first objective is achieved thanks to the possibilities afforded by the Bifrost code. Via 2.5D R-MHD experiments of magnetic flux emergence from the solar layers beneath the surface up to the corona, we have found that a surge is formed in spite of the prior interaction of the the emerging field with the granular cells at and below the surface. The surge detaches from the emerged region as a consequence of strong shocks that develop following the impact of plasmoids ejected along the current sheet in the reconnection site. The surge plasma elements experience accelerations well in excess of the solar gravity value in the onset phase, while it undergoes free-fall in the central and decay phases. Using detailed Lagrange tracing, we have discerned different populations with distinct evolutionary patterns within the surge, some of them directly related to the heating/cooling processes included as part of the Bifrost code. In fact, we have found that a non-small fraction of the surge could not be obtained in previous and more idealized experiments because of the lack of a proper treatment of the thermodynamics and entropy sources. The second goal of the thesis has been accomplished through the observation of an episode of simultaneous occurrence of an Hα surge and of a UV burst obtained with the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS), respectively. Although surges are traditionally related to chromospheric lines, we have found that they can exhibit enhanced UV emission in TR lines of Si IV with brighter and broader spectral profiles than the average TR. Furthermore, we have provided additional observational evidence to support the common origin and relationship between surges and UV bursts. The third objective is achieved by means of forward modeling of numerical experiments that include nonequilibrium ionization of key elements in the TR like silicon and oxygen. The results show that the TR enveloping the surge is strongly affected by nonequilibrium ionization effects, noticeably increasing the number of emitters of the main lines of Si IV and O IV. The departure from statistical equilibrium is due to the short characteristic times of the optically-thin losses and heat conduction during the surge evolution. In addition, we have concluded that line-of-sight effects are important to understand prominent and spatially intermittent Si IV and O IV brightenings within the surges. Finally, the last goal of this thesis has been accomplished through the creation of a new module in the Bifrost code that implements the Super Time-Stepping (STS) method to speed up the calculation of the ambipolar diffusion term. After carrying out an in-depth analysis of the method, we have found the optimum combination of parameters that ensures stability and efficiency. As a first instance of work to be completed in the postdoctoral phase, in the final chapter we have started to explore the effects of ambipolar diffusion on the magnetic flux emergence process leading to the surge phenomenon and in the surge itself.