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Solar Energetic Particles (SEP) events are interesting from a scientific perspective as they are the product of a broad set of physical processes from the corona out through the extent of the heliosphere, and provide insight into processes of particle acceleration and transport that are widely applicable in astrophysics. From the operations perspective, SEP events pose a radiation hazard for aviation, electronics in space, and human space exploration, in particular for missions outside of the Earth’s protective magnetosphere including to the Moon and Mars. Thus, it is critical to imific understanding of SEP events and use this understanding to develop and improve SEP forecasting capabilities to support operations. Many SEP models exist or are in development using a wide variety of approaches and with differing goals. These include computationally intensive physics-based models, fast and light empirical models, machine learning-based models, and mixed-model approaches. The aim of this paper is to summarize all of the SEP models currently developed in the scientific community, including a description of model approach, inputs and outputs, free parameters, and any published validations or comparisons with data.

While there has been a proliferation of interest and research into work-family studies we know little about how employees who study while working manage their multiple and sometimes conflicting roles. This research focuses on non-traditional students (NTS), whose representation in the general student population has increased, and explores how they attempt to balance their work and school responsibilities. The question of what factors potentially impact NTS's academic and job satisfaction remains mostly unanswered and is the question this article attempts to address. Data were collected from over 200 non-traditional students studying across different regional campuses of a US university, testing several hypotheses including relevant demographic and non-demographic variables. Results revealed academic satisfaction was impacted by job-related factors while job satisfaction tended to be influenced mostly by factors in the general work domain. Demographic factors did not appear to predict job satisfaction and nor did they significantly predict academic satisfaction. The paper outlines some future opportunities for research to better understand the work-school dynamic in the lives of non-traditional students.

After exactly 9 years of operations, the SOLAR mission was ended on 15 February 2017. This was an extraordinary achievement knowing the mission was originally set to only last for 1.5 years! SOLAR is a payload of the European Space Agency (ESA), mounted on one of the external platforms of the Columbus module of the International Space Station (ISS). The SOLAR platform hosts three instruments built to observe the spectral solar irradiance in the wavelength range 17 to 3080nm. The Belgian User Support Operations Centre (B.USOC) is the ESA Facility Responsible Centre that supported the operations for SOLAR throughout the whole mission, from the operations preparation to the first few commands sent, handling unexpected problems and operating the instrument with confidence to finally permanently switching it off after 9 years of successful operations. Nevertheless, the mission was of course not free of technical challenges, but these were always handled with the greatest attention to find a suitable solution that would have the least impact on the smooth continuation of the operations. This paper will present the operations constraints experienced by the payload operations team while operating SOLAR and how these challenges were overcome. Constraints covered by the paper include problems related to the ISS attitude and orbit, the mechanical limitations of the instrument, the availability of the various ISS resources, the external influences to the payload operations coming from the ISS itself and from other payloads, the instrument’s operational modes and the instrument’s degradation with time. This list is furthermore complemented by an overview of the operations products needed for dealing with these constraints during operations. Additionally, the so-called Sun Visibility Window bridging will also be mentioned, describing how a scientific requirement that could initially not be fulfilled by the platform as-built could still be occasionally reached by requesting attitude changes of the ISS at well-defined seasonal periods of the year. The paper will be concluded with some valuable lessons learned drawn from the solid experience gained after a 9-year long mission, which can bring useful advise to other teams planning operations of external payloads on the ISS or even to internal payloads, as some encountered constraints can apply to them too. This paper complements the abstract submitted by A. Michel et al. covering the evolution of the operational concept of the SOLAR mission.

For more than seven years, the Belgian User Support and Operations Centre (B.USOC) is operating the Solar Monitoring Observatory (SOLAR) – an experiment of the European Space Agency (ESA), hosted on one of the external platforms of the Columbus module on the International Space Station (ISS). Since the beginning of SOLAR operations, B.USOC has invested in developing tools to support and to guarantee high quality operations. The Yet Another Mission Control System (Yamcs) software, a lightweight Mission Control System (MCS) developed and deployed at B.USOC as an extension of the standard ESA Columbus MCS, allows the SOLAR Operators to monitor the telemetry, to quickly browse the data archive, and to perform replays of events. Due to cost saving measures at the Columbus Control Centre in Munich, from January 2014 on the B.USOC team was obligated to provide 24/7 on-console service, demanding a huge effort from the small team. Therefore, the Yamcs software was extended with a notification tool which allowed B.USOC to return to nominal shift coverage. The papers presents this software extension called “The Yamcs Notification Add-on” (TYNA). TYNA actively monitors all the SOLAR telemetry data and the connections between the different servers and notifies the on-call Operators in case of anomalies. Via a web-interface it is possible to define different monitoring rules, as well as the type of notification, and who will be notified. One can choose between notification via email, text message, phone call, or a combination. The monitoring rules define the content of the TYNA message, which allows a quick assessment of the occurred anomaly by the on-call Operator. As the SOLAR telemetry can be accessed remotely from any workstation with the Yamcs software, the SOLAR Operator can quickly assess the nature of the anomaly as being a payload issue, an on-board system anomaly, or a ground segment problem, and inform the counterparts and take adequate countermeasures. TYNA started monitoring the SOLAR payload on 15th July 2014 and allowed to reduce the on-console service from 24/7 to 16/7 shift coverage when the payload is generating science data, and nominal working hours during periods when the payload is in idle mode. While currently only applied for the SOLAR payload, the TYNA software has been validated to interface with the commonly used ESA MCS tools applied in the Columbus Payload Data Center (CD-MCS) and to monitor the other ESA payloads and Columbus System Telemetry. Both Yamcs and TYNA, developed with the support of ESA, are open source software and free of use for the ISS payload community.

During the last 7 years, the Belgian User Support and Operations Centre (B.USOC) – a Facility Responsible Centre for the European Space Agency (ESA) - has been operating different ESA payloads on the International Space Station with outstanding results. Some key factors of this success are the people in the team, and the strategy applied to balance life and work in such a demanding world as operations for human space flight. The stress and tensions between the different Operators that could generate a negative atmosphere was converted into a positive vibe of opportunities and advantages for everybody. The paper presents the applied human resource strategy which relies, on one hand, on the conversion of a working constraint into flexibility for the people depending on their needs, and on the other hand, on a team composed on purpose of heterogeneous profiles and with very different lifestyles. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA.

Large-scale solar eruptions, known as coronal mass ejections (CMEs), are regarded as the main drivers of space weather. The exact trigger mechanism of these violent events is still not completely clear; however, the solar magnetic field indisputably plays a crucial role in the onset of CMEs. The strength and morphology of the solar magnetic field are expected to have a decisive effect on CME properties, such as size and speed. This study aims to investigate the evolution of a magnetic configuration when driven by the emergence of new magnetic flux in order to get a better insight into the onset of CMEs and their magnetic structure. The three-dimensional, time-dependent equations for ideal magnetohydrodynamics are numerically solved on a spherical mesh. New flux emergence in a bipolar active region causes destabilisation of the initial stationary structure, finally resulting in an eruption. The initial magnetic topology is suitable for the ‘breakout’ CME scenario to work. Although no magnetic flux rope structure is present in the initial condition, highly twisted magnetic field lines are formed during the evolution of the system as a result of internal reconnection due to the interaction of the active region magnetic field with the ambient field. The magnetic energy built up in the system and the final speed of the CME depend on the strength of the overlying magnetic field, the flux emergence rate, and the total amount of emerged flux. The interaction with the global coronal field makes the eruption a large-scale event, involving distant parts of the solar surface.

Coronal mass ejections (CMEs) play a key role in space weather. The mathematical modelling of these violent solar phenomena can contribute to a better understanding of their origin and evolution and as such improve space weather predictions. We review the state-of-the-art in CME simulations, including a brief overview of current models for the background solar wind as it has been shown that the background solar wind affects the onset and initial evolution of CMEs quite substantially. We mainly focus on the attempt to retrieve the initiation and propagation of CMEs in the framework of computational magnetofluid dynamics (CMFD). Advanced numerical techniques and large computer resources are indispensable when attempting to reconstruct an event from Sun to Earth. Especially the simulations developed in dedicated event studies yield very realistic results, comparable with the observations. However, there are still a lot of free parameters in these models and ad hoc source terms are often added to the equations, mimicking the physics that is not really understood yet in detail. (C) 2010 Elsevier Ltd. All rights reserved. ispartof: Journal of Atmospheric and Solar-terrestrial Physics vol:73 issue:10 pages:1148-1155 status: published

In the context of space weather forecasting, an automated detection of coronal mass ejections (CMEs) becomes more and more important for efficiently handling a large data flow which is expected from recently-launched and future solar missions. In this paper we validate the detection software package "CACTus" by applying the program to synthetic data from our 3D time-dependent CME simulations instead of observational data. The main strength of this study is that we know in advance what should be detected. We describe the sensitivities and strengths of automated detection, more specific for the CACTus program, resulting in a better understanding of CME detection on one hand and the calibration of the CACTus software on the other hand, suggesting possible improvements of the package. In addition, the simulation is an ideal tool to investigate projection effects on CME velocity measurements. ispartof: Solar Physics vol:270 issue:1 pages:253-272 status: published

Over the last few years coronagraphic and spectroscopic observations have demonstrated that small-scale eruptions, such as "jets," "narrow coronal mass ejections (CMEs)," "mini CMEs," "streamer puffs," "streamer detachments," and others, occur ubiquitously on the Sun. Nevertheless, the origin of small-scale eruptive events and how these are interrelated with larger scale CMEs have been poorly investigated so far. In this work, we study a series of small-scale side eruptions that occurred during and after a large-scale CME. Observations show that a CME can be associated not only with a single reconnection process, leading to the large-scale phenomenon, but also with many other side reconnections occurring at different locations and times around the main flux rope, possibly induced by the CME expansion in the surrounding corona. White light and EUV observations of a slow CME acquired by the SOHO/LASCO and SOHO/UVCS instruments are analyzed here to characterize the locations of side reconnections induced by the CME. The magnetic reconnection rate M has been estimated from the UVCS data from the ratio between the inflows and outflows observed around the reconnection region, and from the LASCO data from the observed aperture angles between the slow mode shocks (SMSs) associated with the reconnection. It turns out that M 0.05 at the heliocentric distance of 1.8 R , while between ~2.5 and 5.5 R , M values progressively decrease with time/altitude from M ~ 1 down to M ~ 0.3. Such large values of M are theoretically acceptable only if flux pile-up reconnection is envisaged. The observed occurrence of multiple reconnections associated with a CME is verified by numerical simulations of an eruption occurring within multiple helmet streamers. The simulations confirm that small side reconnections are a consequence of CME expansion against the surrounding coronal streamers. The simulated and observed evolution of aperture angles between the SMSs are in good agreement as well. These results demonstrate the effect of the global coronal magnetic field in the occurrence of small-scale eruptions due to lateral reconnection in a preceding CME event. ispartof: Astrophysical Journal vol:718 issue:1 pages:251-265 status: published

We discuss features of coronal mass ejections (CMEs) that are specific to heliospheric observations at large elongation angles. Our analysis is focused on a series of two eruptions that occurred on 2007 January 24-25, which were tracked by the Heliospheric Imagers (HIs) onboard STEREO. Using a three-dimensional (3-D) magneto-hydrodynamic simulation of these ejections with the Space Weather Modeling Framework (SWMF), we illustrate how the combination of the 3-D nature of CMEs, solar rotation, and geometry associated with the Thomson sphere results in complex effects in the brightness observed by the HIs. Our results demonstrate that these effects make any in-depth analysis of CME observations without 3-D simulations challenging. In particular, the association of bright features seen by the HIs with fronts of CME-driven shocks is far from trivial. In this Letter, we argue that, on 2007 January 26, the HIs observed not only two CMEs, but also a dense corotating stream compressed by the CME-driven shocks., Comment: 5 pages, 2 figures, accepted for ApJ Letter

We consider an expanding three-dimensional (3-D) piston as a driver of an MHD shock wave. It is assumed that the source-region surface accelerates over a certain time interval to achieve a particular maximum velocity. Such an expansion creates a large-amplitude wave in the ambient plasma. Owing to the nonlinear evolution of the wavefront, its profile steepens and after a certain time and distance a discontinuity forms, marking the onset of the shock formation. We investigate how the formation time and distance depend on the acceleration phase duration, the maximum expansion velocity (defining also acceleration), the Alfvén velocity (defining also Mach number), and the initial size of the piston. The model differs from the 1-D case, since in the 3-D evolution, a decrease of the wave amplitude with distance must be taken into account. We present basic results, focusing on the timing of the shock formation in the low- and high-plasma-beta environment. We find that the shockformation time and the shock-formation distance are (1) approximately proportional to the acceleration phase duration ; (2) shorter for a higher expansion velocity ; (3) larger in a higher Alfvén speed environment ; (4) only weakly dependent on the initial source size ; (5) shorter for a stronger acceleration ; and (6) shorter for a larger Alfvén Mach number of the source surface expansion. To create a shock causing a high-frequency type II burst and the Moreton wave, the source region expansion should, according to our results, achieve a velocity on the order of 1000 km s− 1 within a few minutes, in a low Alfvén velocity environment.

The CMS Data Acquisition (DAQ) System relies on a purely software driven High Level Trigger (HLT) to reduce the full Level-1 accept rate of 100 kHz to approximately 100 Hz for archiving and later offline analysis. The HLT operates on the full information of events assembled by an event builder collecting detector data from the CMS front-end systems. The HLT software consists of a sequence of reconstruction and filtering modules executed on a farm of 0(1000) CPUs built from commodity hardware. This paper presents the architecture of the CMS HLT, which integrates the CMS reconstruction framework in the online environment. The mechanisms to configure, control, and monitor the Filter Farm and the procedures to validate the filtering code within the DAQ environment are described.

The initiation and evolution of coronal mass ejections (CMEs) is studied by means of the breakout model embedded in a 2.5D axisymmetric solar wind in the framework of numerical magnetohydrodynamics (MHD). The initial, steady equilibrium contains a pre-eruptive region consisting of three arcades with alternating magnetic flux polarity and with correspondingly three neutral lines on the photosphere. The magnetic tension of the overlying closed magnetic field of the helmet streamer keeps this structure in place. The most crucial part of the initial breakout topology is the existence of an X-point on the leading edge of the central arcade. By shearing part of this arcade, the reconnection with the overlying streamer field is turned on. The initial phase of the erupting arcade then closely follows the original breakout scenario. The breakout reconnection opens the overlying field in an energetically efficient way leading to an ever faster eruption. However, from a certain moment two new reconnections set in on the sides of the erupting central arcade and the breakout reconnection stops. The consequence of this change in reconnection location is twofold: (1) the lack of breakout reconnection so that the breakout plasmoid fails to become a fast CME; and (2) an eventual disconnection of the large helmet top resulting in a slow CME.

Context. The shocks and magnetic clouds related to Coronal Mass Ejections (CMEs) in the solar corona and interplanetary space (IP) play an important role in the study of space weather. In order to study the evolution of these IP shocks, numerical simulations of a simplified CME model were performed. Aims. In an earlier study, the effect of the background wind on the evolution of interplanetary shock waves was investigated, where the computations were carried out under the assumption of axial symmetry. The assumption of axial symmetry might be a good approach for the solar corona under conditions of solar minimum, but for the study of CMEs this assumption is definitely no longer valid as CMEs possess clearly a fully three dimensional (3D) structure. From this perspective, the previous simulations were repeated, but now in a three dimensional set-up in order to point out the differences between the 2.5D and 3D simulations and to check the quality and reliability of the 2.5D simulations. Methods. The computations were performed in the framework of ideal magnetohydrodynamics (MHD) and to advance the ideal MHD equations in time a parallel finite volume code with explicit upwind solver was used. The shock waves are generated in a similar way in both the 3D and 2.5D simulations, namely by a simple density-blob model. The 3D and 2.5D simulations are all performed with the same numerical methods and on comparable grids, such that the differences between the simulations are purely due to the dimensionality of the problem, and/or the initial parameters for the CME generation. Results. Three different axisymmetric simulations of CME propagation are compared with the fully three dimensional computation. The 2.5D simulations differ from each other in the parameters used for CME initiation. In a first simulation, the same initial parameters as for the 3D case were taken, in a second simulation the initial amount of mass in the 2.5D and 3D CME was the same, and in a third simulation they had a comparable amount of momentum. It turned out that the latter one compared best with the 3D results. Conclusions. As 2.5D computations are computationally much cheaper than 3D computations, we conclude that the 2.5D simulations of the CME evolution are a good first approach and resemble well the 3D result, provided that the appropriate initiation parameters are chosen.

We report on numerical simulations of the evolution of two-dimensional detonation waves that are expanded from a small channel to a larger one. In accordance with experimental data, the simulations predict three different types of evolution, namely, supercritical, critical and subcritical detonations. In a supercritical detonation, the reaction zone remains always attached to the precursor shock, whereas in a critical one it temporarily detaches and then re-attaches to the front. In the subcritical type, the extinction is permanent, i.e., the detonation quenches. The effects of the fuel's activation energy and the channel-width ratio are studied via a parametric study. It is found that sufficiently large values of these two parameters can result to flows of the critical and even the subcritical type. Finally, three-dimensional simulations have also been performed and are briefly discussed herein. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Context. Photospheric motions and a sheared configuration of the magnetic field are often considered as precursors of violent solar phenomena such as flares and Coronal Mass Ejections (CMEs). Therefore, in many numerical CME initiation studies shearing of the magnetic foot points is used as a mechanism to make the magnetic field unstable and to trigger the CME event. Aims. From that point of view we decided to do a parameter study that investigates the effect of the different initiation parameters, in particular the effect of the shear flow velocity. Moreover, the simulations were performed on three different background solar wind models. In this way, both effects of the background wind and the initiation parameters on the CME evolution are quantified. Methods. The results are obtained by means of a finite volume, explicit solver to advance the equations of ideal magnetohydrodynamics. All simulations involve the same numerical grid, the same numerical technique and similar boundary conditions, so that the results can be compared in an unequivocal way. Results. The foot points of the magnetic field lines are sheared by introducing an extra longitudinal flow profile on the solar surface with a maximum velocity ranging from 3 km s -1 to 9 km s -1 . The temporal evolution of the magnetic energy, the velocity of the flux rope, and the magnetic helicity show a dependence on the maximum shear velocity as well as on the background wind model.

Simulations of Coronal Mass Ejections (CMEs) evolving in the interplanetary (IP) space from the Sun up to 1 AU are performed in the framework of ideal magnetohydrodynamics (MHD) by the means of a finite volume, explicit solver. The aim is to quantify the effect of the initiation parameters, such as the initial magnetic polarity, on the evolution and on the geo-effectiveness of CMEs. The CMEs are simulated by means of a very simple model: a high density and high pressure magnetized plasma blob is superposed on a background steady state solar wind model with an initial velocity and launch direction. The simulations show that the initial magnetic polarity substantially affects the IP evolution of the CMEs influencing the propagation velocity, the shape, the trajectory and even the geo-effectiveness. We also tried to reproduce the physical values (density, velocity, and magnetic field) observed by the ACE spacecraft after the halo CME event that occurred on April 4, 2000.

The shocks and magnetic clouds caused by Coronal Mass Ejections (CMEs) in the solar corona and interplanetary (IP) space play an important role in the study of space weather. In the present paper, numerical simulations of some simple CME models were performed by means of a finite volume, explicit solver to advance the equations of ideal magnetohydrodynamics. The aim is to quantify here both the effect of the background wind model and of the initial polarity on the evolution of the IP CMEs and the corresponding shocks. To simulate the CMEs, a high density-pressure plasma blob is superposed on different steady state solar wind models. The evolution of an initially non-magnetized plasma blob is compared with that of two magnetized ones (with both normal and inverse polarity) and the differences are analysed and quantified. Depending on the launch angle of the CME and the polarity of the initial flux rope, the velocity of the shock front and magnetic cloud is decreased or increased. Also the spread angle of the CME and the evolution path of the CME in the background solar wind is substantially different for the different CME models and the different wind models. A quantitative comparison of these simulations shows that these effects can be quite substantial and can clearly affect the geo-effectiveness and the arrival time of the events.

The propagating shock waves in the solar corona and interplanetary (IP) space caused by fast Coronal Mass Ejections (CMEs) are simulated numerically and their structure and evolution is studied in the framework of ideal magnetohydrodynamics (MHD). Due to the presence of three characteristic velocities and the anisotropy induced by the magnetic field, the CME shocks generated in the lower corona can have a complex structure and topology including secondary shock fronts, over-compressive and compound shocks, etc. The evolution of these CME shocks is followed during their propagation in IP space up to r = 30 R� . Here, particular attention is given to the effect of the background solar wind on the evolution parameters of the fast CME shocks, i.e. shock speed, deformation of the leading shock front and the CME plasma, stand-off distance of the leading shock front, direction, spread angle, etc. First, different "frequently used" solar wind models are reconstructed with the same numerical code, the same numerical technique on exactly the same numerical grid (and thus the same numerical dissipation), the same boundary conditions, and the same normalization. Then, a simple CME model is superposed on three different solar wind models, again using exactly the same initial conditions. The result is a fair comparison and thus an objective study of the effect of the background wind on the CME shock evolution. This effect is surprisingly substantial and can be quantified due to the uniformity of the normalization of the used models and simulation techniques.

© J. Pomoell et al., Published by EDP Sciences 2015. We have developed a new version of a model that combines a two-dimensional Sun-to-Earth magnetohydrodynamic (MHD) simulation of the propagation of a CME-driven shock and a simulation of the transport of particles along the interplanetary magnetic field (IMF) line connecting the shock front and the observer. We assume that the shock-accelerated particles are injected at the point along the shock front that intersects this IMF line, i.e. at the cobpoint. Novel features of the model are an improved solar wind model and an enhanced fully automated algorithm to extract the necessary plasma characteristics from the shock simulation. In this work, the new algorithms have been employed to simulate the 2000 April 4 and the 2006 December 13 SEP events. In addition to quantifying the performance of the new model with respect to results obtained using previous versions of the shock-and-particle model, we investigate the semi-empirical relation between the injection rate of shock-accelerated particles, Q, and the jump in speed across the shock, VR, known as the Q(VR) relation. Our results show that while the magnetic field and density compression at the shock front is markedly different than in our previous modeling, the evolution of VR remains largely similar. As a result, we confirm that a simple relation can still be established between Q and VR, which enables the computation of synthetic intensity-time profiles at any location in interplanetary space. Furthermore, the new shock extraction tool is found to yield improved results being in general more robust. These results are important not only with regard to efforts to develop coupled magnetohydrodynamic and particle simulation models, but also to improve space weather related software tools that aim to predict the peak intensities, fluences and proton intensity-time profiles of SEP events (such as the SOLPENCO tool). ispartof: Journal of Space Weather and Space Climate vol:5 status: published

The Solar Monitoring Observatory (SOLAR) is a payload of the European Space Agency (ESA) mounted on the zenith-pointing external platform of the Columbus module of the International Space Station (ISS) and is designed to track the Sun in order to perform quasi-continuous measurements of the solar irradiance. SOLAR is operational and returning science since February 2008 and its mission is supported until February 2017. This paper presents the “SOLAR Predictor", a web-based knowledge management tool. The tool has been developed by the operator team at the Belgian User Support and Operations Centre (B.USOC) in 2012 to support the operations of SOLAR within the team and it was further fine-tuned in 2013. The SOLAR Predictor aims to collect and combine all the latest information relevant to SOLAR operations at a single location, in order to support and facilitate routine operator tasks The SOLAR Predictor tool automatically fetches and parses information from a series of sources relevant to SOLAR Operations, like real-time planning, attitude timeline and vehicle traffic, orbitrelated data and of course the SOLAR telemetry data. The tool also links to a database containing SOLAR specific command schedules. These command scripts are used onboard to execute the science activities. The implementation in the Predictor is as such that it provides a means of configuration control, on-board file management, and support for file uplink and transfer. The algorithms implemented in the Predictor tool process the data feed in order to provide predictions of Sun observation conditions and operations constraints based on the latest available information. The information is graphically visualised, highlighting possible conflicts in the planning, allowing the operators to easily fine-tune the planning. The tool facilitates the long-term planning and real-time rescheduling of the science activities, based on the input from the science teams. At the time of activity execution, the operator is warned through an audible alarm. The daily timeline reviews are supported by automatically checking the differences between the desired planning and the published Onboard Short Term Plan data, and by automatically generating the input files for the various operational counterparts. Finally, the tool automatically creates detailed and accurate Daily Operations Reports, which are distributed to the SOLAR stakeholders. The SOLAR Predictor tool helps maximizing the scientific return of operations within the existing

The data acquisition system for the CMS experiment at the Large Hadron Collider (LHC) will require a large and high performance event building network. Several switch technologies are currently being evaluated in order to compare different architectures for the event builder. One candidate is Myrinet. This paper describes the demonstrator which has been setup to study a small-scale (16×16) event builder based on PCs running Linux connected to Myrinet and Ethernet switches. A detailed study of the Myrinet switch performance has been performed for various traffic conditions, including the behaviour of composite switches. Results from event building studies are presented, including measurements on throughput, overhead and scaling. Traffic shaping techniques have been implemented and the effect on the event building performance has been investigated. The paper reports on performances and maximum event rate obtainable using custom software, not described, for the Myrinet control program and the low-level communication layer, implemented in a driver for Linux. A high performance sender is emulated by creating a dummy buffer that remains resident in the network interface and moving from the host only the first 64 bytes used by the event building protocol. An approximate scaling in N is presented assuming a balanced system where each source sends on average data to all destinations with the same rate.

A recent study by Cid et al. (2012) showed that full halo coronal mass ejections (CMEs) coming from the limb can disturb the terrestrial environment. Although this result seems to rise some controversies with the well established theories, the fact is that the study encourages the scientific community to perform careful multidisciplinary analysis along the Sunto- Earth chain to fully understand which are the solar triggers of terrestrial disturbances. This paper aims to clarify some of the polemical issues arisen by that paper. © 2013 International Astronomical Union. Fil:Mandrini, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

High-energy charged particles in the van Allen radiation belts and in solar energetic particle events can damage satellites on orbit leading to malfunctions and loss of satellite service. Here we describe some recent results from the SPACECAST project on modelling and forecasting the radiation belts, and modelling solar energetic particle events. We describe the SPACECAST forecasting system that uses physical models that include wave-particle interactions to forecast the electron radiation belts up to 3 h ahead. We show that the forecasts were able to reproduce the >2 MeV electron flux at GOES 13 during the moderate storm of 7-8 October 2012, and the period following a fast solar wind stream on 25-26 October 2012 to within a factor of 5 or so. At lower energies of 10 - a few 100 keV we show that the electron flux at geostationary orbit depends sensitively on the high-energy tail of the source distribution near 10 R E on the nightside of the Earth, and that the source is best represented by a kappa distribution. We present a new model of whistler mode chorus determined from multiple satellite measurements which shows that the effects of wave-particle interactions beyond geostationary orbit are likely to be very significant. We also present radial diffusion coefficients calculated from satellite data at geostationary orbit which vary with K p by over four orders of magnitude. We describe a new automated method to determine the position at the shock that is magnetically connected to the Earth for modelling solar energetic particle events and which takes into account entropy, and predict the form of the mean free path in the foreshock, and particle injection efficiency at the shock from analytical theory which can be tested in simulations. © R.B. Horne et al., Published by EDP Sciences 2013. ispartof: Journal of Space Weather and Space Climate vol:3 status: published

[1] The probability for a halo coronal mass ejection (CME) to be geoeffective is assumed to be higher the closer the CME launch site is located to the solar central meridian. However, events far from the central meridian may produce severe geomagnetic storms, like the case in April 2000. In this work, we study the possible geoeffectiveness of full halo CMEs with the source region situated at solar limb. For this task, we select all limb full halo (LFH) CMEs that occurred during solar cycle 23, and we search for signatures of geoeffectiveness between 1 and 5 days after the first appearance of each CME in the LASCO C2 field of view. When signatures of geomagnetic activity are observed in the selected time window, interplanetary data are carefully analyzed in order to look for the cause of the geomagnetic disturbance. Finally, a possible association between geoeffective interplanetary signatures and every LFH CME in solar cycle 23 is checked in order to decide on the CME's geoeffectiveness. After a detailed analysis of solar, interplanetary, and geomagnetic data, we conclude that of the 25 investigated events, there are only four geoeffective LFH CMEs, all coming from the west limb. The geoeffectiveness of these events seems to be moderate, turning to intense in two of them as a result of cumulative effects from previous mass ejections. We conclude that ejections from solar locations close to the west limb should be considered in space weather, at least as sources of moderate disturbances.

On 2009 September 21, a filament eruption and the associated Coronal Mass Ejection (CME) was observed by the STEREO spacecraft. The CME originated from the southern hemisphere and showed a deflection of about 15° towards the heliospheric current sheet (HCS) during its propagation in the COR1 field-of-view (FOV). The aim of this paper is to provide a physical explanation for the strong deflection of the CME. We first use the STEREO observations in order to reconstruct the three dimensional (3D) trajectory of the CME. Starting from a magnetic configuration that closely resembles the potential field extrapolation for that date, we performed numerical magneto-hydrodynamics (MHD) simulations. By applying localized shearing motions, a CME is initiated in the simulation, showing a similar non-radial evolution, structure, and velocity as the observed event. The CME gets deflected towards the current sheet of the larger northern helmet streamer, due to an imbalance in the magnetic pressure and tension forces and finally it gets into the streamer and propagates along the heliospheric current sheet. © 2012 International Astronomical Union. ispartof: pages:134-138 ispartof: Comparative Magnetic Minima: characterizing quiet times in the Sun and stars vol:286 issue:286 pages:134-138 ispartof: IAU Symposium No. 286, 2011 location:ARGENTINA, Mendoza date:3 Oct - 7 Oct 2011 status: published

The solar wind fills the heliosphere and is the background medium in which coronal mass ejections propagate. A realistic modelling of the solar wind is therefore essential for space weather research and for reliable predictions. Although the solar wind is highly anisotropic, magnetohydrodynamic (MHD) models are able to reproduce the global, average solar wind characteristics rather well. The modern computer power makes it possible to perform full three dimensional (3D) simulations in domains extending beyond the Earth's orbit, to include observationally driven boundary conditions, and to implement even more realistic physics in the equations. In general, MHD models for the solar wind often make use of additional source and sink terms in order to mimic the observed solar wind parameters and/or they hide the not-explicitly modelled physical processes in a reduced or variable adiabatic index. Even the models that try to take as much as possible physics into account, still need additional source terms and fine tuning of the parameters in order to produce realistic results. In this paper we present a new and simple polytropic model for the solar wind, incorporating data from the ACE spacecraft to set the model parameters. This approach allows to reproduce the different types of solar wind, where the simulated plasma variables are in good correspondence with the observed solar wind plasma near 1 AU. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. ispartof: Advances in Space Research vol:48 issue:12 pages:1958-1966 status: published

In this study, we test the flux rope paradigm by performing a "blind" reconstruction of the magnetic field structure of a simulated interplanetary coronal mass ejection (ICME). The ICME is the result of a magnetohydrodynamic numerical simulation and does not exhibit much magnetic twist, but appears to have some characteristics of a magnetic cloud, due to a writhe in the magnetic field lines. We use the Grad-Shafranov technique with simulated spacecraft measurements at two different distances and compare the reconstructed magnetic field with that of the ICME in the simulation. While the reconstructed magnetic field is similar to the simulated one as seen in two dimensions, it yields a helically twisted magnetic field in three dimensions. To further verify the results, we perform the reconstruction at three different position angles at every distance point, and all results are found to be in agreement. This work demonstrates that the current paradigm of associating magnetic clouds with flux ropes may have to be revised. ispartof: The Astrophysical Journal. Letters vol:738 issue:2 status: published

The discipline of "Space Weather" is built on the scientific foundation of solar-terrestrial physics but with a strong orientation toward applied research. Models describing the solar-terrestrial environment are therefore at the heart of this discipline, for both physical understanding of the processes involved and establishing predictive capabilities of the consequences of these processes. Depending on the requirements, purely physical models, semi-empirical or empirical models are considered to be the most appropriate. This review focuses on the interaction of solar wind disturbances with geospace. We cover interplanetary space, the Earth's magnetosphere (with the exception of radiation belt physics), the ionosphere (with the exception of radio science), the neutral atmosphere and the ground (via electromagnetic induction fields). Space weather relevant state-of-the-art physical and semi-empirical models of the various regions are reviewed. They include models for interplanetary space, its quiet state and the evolution of recurrent and transient solar perturbations (corotating interaction regions, coronal mass ejections, their interplanetary remnants, and solar energetic particle fluxes). Models of coupled large-scale solar wind-magnetosphere-ionosphere processes (global magnetohydrodynamic descriptions) and of inner magnetosphere processes (ring current dynamics) are discussed. Achievements in modeling the coupling between magnetospheric processes and the neutral and ionized upper and middle atmospheres are described. Finally we mention efforts to compile comprehensive and flexible models from selections of existing modules applicable to particular regions and conditions in interplanetary space and geospace. ispartof: Space Science Reviews vol:147 issue:3 pages:233-270 status: published

Context. Coronal mass ejections (CMEs) are enormous expulsions of magnetic flux and plasma from the solar corona into the interplanetary space. These phenomena release a huge amount of energy. It is generally accepted that both photospheric motions and the emergence of new magnetic flux from below the photosphere can put stress on the system and eventually cause a loss of equilibrium resulting in an eruption. Aims. By means of numerical simulations we investigate both emergence of magnetic flux and shearing motions along the magnetic inversion line as possible driver mechanisms for CMEs. The pre-eruptive region consists of three arcades with alternating magnetic flux polarity, favouring the breakout mechanism. Methods. The equations of ideal magnetohydrodynamics (MHD) were advanced in time by using a finite volume approach and solved in spherical geometry. The simulation domain covers a meridional plane and reaches from the lower solar corona up to 30 . When we applied time-dependent boundary conditions at the inner boundary, the central arcade of the multiflux system expands, leading to the eventual eruption of the top of the helmet streamer. We compare the topological and dynamical evolution of the system when driven by the different boundary conditions. The available free magnetic energy and the possible role of magnetic helicity in the onset of the CME are investigated. Results. In our simulation setup, both driving mechanisms result in a slow CME. Independent of the driving mechanism, the overall evolution of the system is the same: the actual CME is the detatched helmet streamer. However, the evolution of the central arcade is different in the two cases. The central arcade eventually becomes a flux rope in the shearing case, whereas in the flux emergence case there is no formation of a flux rope. Furthermore, we conclude that magnetic helicity is not crucial to a solar eruption. ispartof: Astronomy & astrophysics vol:507 issue:1 pages:441-452 status: published

Eruption of a coronal mass ejection (CME) drags and "opens" the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and the field relaxation by magnetic reconnection. We analyze physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to check if the interpretation of this phenomenon in terms of reconnecting current sheet is consistent with the observations. The study is focused on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of rays indicates that they occur as a consequence of Petschek-like reconnection in the large scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km s$^{-1}$, consistent with the narrow opening-angle of rays, adding up to a few degrees. The density of rays is an order of magnitude larger than in the ambient corona. The density-excess measurements are compared with the results of the analytical model in which the Petschek-like reconnection geometry is applied to the vertical current sheet, taking into account the decrease of the external coronal density and magnetic field with height. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to larger heights by the reconnection outflow.

Context. Coronal mass ejections (CMEs) are enormous expulsions of magnetic flux and plasma from the solar corona. Most scientists agree that a coronal mass ejection is the sudden release of magnetic free energy stored in a strongly stressed field. However, the exact reason for this sudden release is still highly debated. Aims. In an initial multiflux system in steady state equilibrium, containing a pre-eruptive region consisting of three arcades with alternating magnetic flux polarity, we study the initiation and early evolution properties of a sequence of CMEs by shearing a region slightly larger than the central arcade. Methods. We solve the ideal magnetohydrodynamics (MHD) equations in an axisymmetrical domain from the solar surface up to 30 R⊙. The ideal MHD equations are advanced in time over a non uniform grid using a modified version of the Versatile Advection Code (VAC). Results. By applying shearing motions on the solar surface, the magnetic field is energised and multiple eruptions are obtained. Magnetic reconnection first opens the overlying field and two new reconnections sites set in on either side of the central arcade. After the disconnection of the large helmet top, the system starts to restore itself but cannot return to its original configuration as a new arcade has already started to erupt. This process then repeats itself as we continue shearing.Conclusions. The simulations reported in the present paper, demonstrate the ability to obtain a sequence of CMEs by shearing a large region of the central arcade or by shearing a region that is only slightly larger than the central arcade. We show, be it in an axisymmetric configuration, that the breakout model can not only lead to confined eruptions but also to actual coronal mass ejections provided the model includes a realistic solar wind model. © 2009 ESO. ispartof: Astronomy & Astrophysics vol:501 issue:3 pages:1123-1130 status: published

Numerical simulations of Coronal Mass Ejections (CMEs) can provide a deeper insight in the structure and propagation of these impressive solar events. In this work, we present our latest results of numerical simulations of the initial evolution of a fast CME. For this purpose, the equations of ideal MagnetoHydroDynamics (MHD) have been solved on a three-dimensional (3D) mesh by means of an explicit, finite volume solver, where the simulation domain ranges from the lower solar corona up to 30R e. In order to simulate the propagation of a CME throughout the heliosphere, a magnetic flux rope is superposed on top of a stationary background solar (MHD) wind with extra density added to the flux rope. The flux rope is launched by giving it an extra initial velocity in order to get a fast CME forming a 3D shock wave. The magnetic field inside the initial flux rope is described in terms of Bessel functions and possesses a high amount of twist.

The possible role of magnetic flux emergence in the initiation of coronal mass ejections (CMEs) is investigated in the framework of the breakout model. The ideal MHD equations are solved numerically on a spherical, axisymmetric (2.5-dimensional) domain. An initial multiflux system in steady equilibrium containing a pre-eruptive region consisting of three arcades with alternating magnetic flux polarity is kept in place by the magnetic tension of the overlying closed magnetic field of a helmet streamer. The emergence of new magnetic flux in the central arcade is simulated by means of a time-dependent boundary condition on the vector potential applied at the solar base. Height-time plots of the ejected material, as well as time evolution of the magnetic, kinetic and internal energy in the entire domain as functions of flux emergence rate, are produced. The results show that the emergence of new magnetic flux in the central arcade triggers a CME. The obtained eruption corresponds to a slow CME, and conversion of magnetic energy into kinetic energy is observed. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A. ispartof: Astrophysical Letters vol:689 issue:2 pages:L157-L160 status: published

The data acquisition system of the CMS experiment at the Large Hadron Collider features a two-stage event builder, which combines data from about 500 sources into full events at an aggregate throughput of 100 GB/s. To meet the requirements, several architectures and interconnect technologies have been quantitatively evaluated. Myrinet will be used for the communication from the underground frontend devices to the surface event building system. Gigabit Ethernet is deployed in the surface event building system. Nearly full bi-section throughput can be obtained using a custom software driver for Myrinet based on barrel shifter traffic shaping. This paper discusses the use of Myrinet dual-port network interface cards supporting channel bonding to achieve virtual 5 GBit/s links with adaptive routing to alleviate the throughput limitations associated with wormhole routing. Adaptive routing is not expected to be suitable for high-throughput event builder applications in high-energy physics. To corroborate this claim, results from the CMS event builder preseries installation at CERN are presented and the problems of wormhole routing networks are discussed.

A review is given of some recent results on CME initiation and evolution simulations obtained at the Centre for Plasma Astrophysics (CPA, K.U.Leuven) on the background of the international developments in this very dynamic field

Simulations of coronal mass ejections (CMEs) evolving in the interplanetary (IP) space from the Sun up to 1 AU are performed in the framework of ideal magnetohydrodynamics (MHD) by the means of a finite-volume, explicit solver. The aim is to quantify the effect of the background solar wind and of the CME initiation parameters, such as the initial magnetic polarity, on the evolution and on the geo-effectiveness of CMEs. First, three different solar wind models are reconstructed using the same numerical grid and the same numerical scheme. Then, different CME initiation models are considered: Magnetic foot point shearing and magnetic flux emergence. For the fast CME evolution studies, a very simple CME model is considered: A high-density and high-pressure magnetized plasma blob is superposed on a background steady state solar wind model with an initial velocity and launch direction. The simulations show that the initial magnetic polarity substantially affects the IP evolution of the CMEs influencing the propagation velocity, the shape, the trajectory (and thus, the geo-effectiveness). ispartof: Space science reviews vol:121 issue:1 pages:91-104 status: published

[1] An accurate tide-generating potential series for Mercury has been calculated on the basis of VSOP87 ephemerides for the solar system planets. Due to the 3:2 spin-orbit resonance, the tides on Mercury cannot be divided into the three classically known tidal frequency bands for the Earth: the diurnal, semidiurnal, and long-period tides. Instead, the tides all have periods of the order of one Mercury day, or, equivalently, one Mercury year, and their amplitudes have been calculated with an accuracy of 10−5 m2s−2. Basic Mercury models with varying inner and outer core radii and core sulfur concentration have been constructed in order to test the sensitivity of tides to these parameters. To determine the reaction of Mercury to the tidal forcing, the Love numbers h, l, and k and the gravimetric factor δ were calculated for the interior models. Tidal displacements, gravity variations, and external gravitational potential variations have also been calculated for the models. It is shown that especially the measurement of the external potential variations will be extremely useful for constraining the inner and outer core.

Nine commercial calcium carbonates, plus 3 calcium carbonates which have been synthesized in the laboratory and 2 natural ones, have been γ-ray irradiated at room temperature. From these 14 samples, 11 are pure calcite, 2 are pure aragonite and 1 is a mixture of calcite and aragonite. Important differences in their ESR spectra are observed. A preheating treatment (up to 600°C) was performed in order to standardize the ESR spectra. After a heating treatment at 600°C for 2 h, all the samples are in the calcite phase; 6 of them mainly exhibit, after γ-ray irradiation, a paramagnetic species with g∥ = 2.0024 and gb = 2.0037 (CO3-3?). A k-value of ≈0.1 for two radiolytic species (one at 2.0052 and the other, anisotropic, at 2.0037 and 2.0024) of three commercial samples of calcite is obtained by means of α-particle irradiation with an 241Am source.