Browsing by Subject "CMES"

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  • Ala-Lahti, Matti; Kilpua, Emilia K. J.; Soucek, Jan; Pulkkinen, Tuija; Dimmock, Andrew P. (2019)
    We report on a statistical analysis of the occurrence and properties of Alfven ion cyclotron (AIC) waves in sheath regions driven by interplanetary coronal mass ejections (ICMEs). We have developed an automated algorithm to identify AIC wave events from magnetic field data and apply it to investigate 91 ICME sheath regions recorded by the Wind spacecraft. Our analysis focuses on waves generated by the ion cyclotron instability. AIC waves are observed to be frequent structures in ICME-driven sheaths, and their occurrence is the highest in the vicinity of the shock. Together with previous studies, our results imply that the shock compression has a crucial role in generating wave activity in ICME sheaths. AIC waves tend to have their frequency below the ion cyclotron frequency, and, in general, occur in plasma that is stable with respect to the ion cyclotron instability and has lower ion beta(parallel to) than mirror modes. The results suggest that the ion beta anisotropy beta(perpendicular to)/beta(parallel to) > 1 appearing in ICME sheaths is regulated by both ion cyclotron and mirror instabilities.
  • Scolini, C.; Chané, E.; Pomoell, J.; Rodriguez, L.; Poedts, S. (2020)
    Predictions of the impact of coronal mass ejections (CMEs) in the heliosphere mostly rely on cone CME models, whose performances are optimized for locations in the ecliptic plane and at 1 AU (e.g., at Earth). Progresses in the exploration of the inner heliosphere, however, advocate the need to assess their performances at both higher latitudes and smaller heliocentric distances. In this work, we perform 3-D magnetohydrodynamics simulations of artificial cone CMEs using the EUropean Heliospheric FORecasting Information Asset (EUHFORIA), investigating the performances of cone models in the case of CMEs launched at high latitudes. We compare results obtained initializing CMEs using a commonly applied approximated (Euclidean) distance relation and using a proper (great circle) distance relation. Results show that initializing high-latitude CMEs using the Euclidean approximation results in a teardrop-shaped CME cross section at the model inner boundary that fails in reproducing the initial shape of high-latitude cone CMEs as a circular cross section. Modeling errors arising from the use of an inappropriate distance relation at the inner boundary eventually propagate to the heliospheric domain. Errors are most prominent in simulations of high-latitude CMEs and at the location of spacecraft at high latitudes and/or small distances from the Sun, with locations impacted by the CME flanks being the most error sensitive. This work shows that the low-latitude approximations commonly employed in cone models, if not corrected, may significantly affect CME predictions at various locations compatible with the orbit of space missions such as Parker Solar Probe, Ulysses, and Solar Orbiter.
  • Lynch, Benjamin J.; Palmerio, Erika; DeVore, C. Richard; Kazachenko, Maria D.; Dahlin, Joel T.; Pomoell, Jens; Kilpua, Emilia K. J. (2021)
    We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a large-scale, high-latitude filament eruption observed by the Solar Dynamics Observatory. We analyze the 2015 July 9-10 filament eruption and the evolution of the resulting coronal mass ejection (CME) through the solar corona. The slow streamer-blowout CME leaves behind an elongated post-eruption arcade above the extended polarity inversion line that is only poorly visible in extreme ultraviolet (EUV) disk observations and does not resemble a typical bright flare-loop system. Magnetohydrodynamic (MHD) simulation results from our data-inspired modeling of this eruption compare favorably with the EUV and white-light coronagraph observations. We estimate the reconnection flux from the simulation's flare-arcade growth and examine the magnetic-field orientation and evolution of the erupting prominence, highlighting the transition from an erupting sheared-arcade filament channel into a streamer-blowout flux-rope CME. Our results represent the first numerical modeling of a global-scale filament eruption where multiple ambiguous and complex observational signatures in EUV and white light can be fully understood and explained with the MHD simulation. In this context, our findings also suggest that the so-called stealth CME classification, as a driver of unexpected or "problem" geomagnetic storms, belongs more to a continuum of observable/nonobservable signatures than to separate or distinct eruption processes.
  • Asvestari, Eleanna; Pomoell, Jens; Kilpua, Emilia; Good, Simon; Chatzistergos, Theodosios; Temmer, Manuela; Palmerio, Erika; Poedts, Stefaan; Magdalenic, Jasmina (2021)
    Context. Coronal mass ejections (CMEs) are a manifestation of the Sun's eruptive nature. They can have a great impact on Earth, but also on human activity in space and on the ground. Therefore, modelling their evolution as they propagate through interplanetary space is essential. Aims. EUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a data-driven, physics-based model, tracing the evolution of CMEs through background solar wind conditions. It employs a spheromak flux rope, which provides it with the advantage of reconstructing the internal magnetic field configuration of CMEs. This is something that is not included in the simpler cone CME model used so far for space weather forecasting. This work aims at assessing the spheromak CME model included in EUHFORIA. Methods. We employed the spheromak CME model to reconstruct a well observed CME and compare model output to in situ observations. We focus on an eruption from 6 January 2013 that was encountered by two radially aligned spacecraft, Venus Express and STEREO-A. We first analysed the observed properties of the source of this CME eruption and we extracted the CME properties as it lifted off from the Sun. Using this information, we set up EUHFORIA runs to model the event. Results. The model predicts arrival times from half to a full day ahead of the in situ observed ones, but within errors established from similar studies. In the modelling domain, the CME appears to be propagating primarily southward, which is in accordance with white-light images of the CME eruption close to the Sun. Conclusions. In order to get the observed magnetic field topology, we aimed at selecting a spheromak rotation angle for which the axis of symmetry of the spheromak is perpendicular to the direction of the polarity inversion line (PIL). The modelled magnetic field profiles, their amplitude, arrival times, and sheath region length are all affected by the choice of radius of the modelled spheromak.
  • Scolini, C.; Rodriguez, L.; Mierla, M.; Pomoell, J.; Poedts, S. (2019)
    Context. Coronal mass ejections (CMEs) are the primary source of strong space weather disturbances at Earth. Their geo-effectiveness is largely determined by their dynamic pressure and internal magnetic fields, for which reliable predictions at Earth are not possible with traditional cone CME models. Aims. We study two well-observed Earth-directed CMEs using the EUropean Heliospheric FORecasting Information Asset (EUH-FORIA) model, testing for the first time the predictive capabilities of a linear force-free spheromak CME model initialised using parameters derived from remote-sensing observations. Methods. Using observation-based CME input parameters, we performed magnetohydrodynamic simulations of the events with EU-HFORIA, using the cone and spheromak CME models. Results. Simulations show that spheromak CMEs propagate faster than cone CMEs when initialised with the same kinematic parameters. We interpret these differences as the result of different Lorentz forces acting within cone and spheromak CMEs, which lead to different CME expansions in the heliosphere. Such discrepancies can be mitigated by initialising spheromak CMEs with a reduced speed corresponding to the radial speed only. Results at Earth provide evidence that the spheromak model improves the predictions of B (B-z) by up to 12-60 (22-40) percentage points compared to a cone model. Considering virtual spacecraft located within +/- 10 degrees around Earth, B (Bz) predictions reach 45-70% (58-78%) of the observed peak values. The spheromak model shows inaccurate predictions of the magnetic field parameters at Earth for CMEs propagating away from the Sun-Earth line. Conclusions. The spheromak model successfully predicts the CME properties and arrival time in the case of strictly Earth-directed events, while modelling CMEs propagating away from the Sun-Earth line requires extra care due to limitations related to the assumed spherical shape. The spatial variability of modelling results and the typical uncertainties in the reconstructed CME direction advocate the need to consider predictions at Earth and at virtual spacecraft located around it.
  • Good, S.W.; Kilpua, E.K.J.; LaMoury, A.T.; Forsyth, R.J.; Eastwood, J.P.; Möstl, C. (2019)
    Abstract Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation, and the evolution of ICME magnetic field structure during propagation, are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east-west direction with heliocentric distance.
  • Verbeke, C.; Pomoell, J.; Poedts, S. (2019)
    Aims. We introduce a new model for coronal mass ejections (CMEs) that has been implemented in the magnetohydrodynamics (MHD) inner heliosphere model EUHFORIA. Utilising a linear force-free spheromak (LFFS) solution, the model provides an intrinsic magnetic field structure for the CME. As a result, the new model has the potential to predict the magnetic components of CMEs at Earth. In this paper, we present the implementation of the new model and show the capability of the new model. Methods. We present initial validation runs for the new magnetised CME model by considering the same set of events as used in the initial validation run of EUHFORIA that employed the Cone model. In particular, we have focused on modelling the CME that was responsible for creating the largest geomagnetic disturbance (Dst index). Two scenarios are discussed: one where a single magnetised CME is launched and another in which we launch all five Earth-directed CMEs that were observed during the considered time period. Four out of the five CMEs were modelled using the Cone model. Results. In the first run, where the propagation of a single magnetized CME is considered, we find that the magnetic field components at Earth are well reproduced as compared to in-situ spacecraft data. Considering a virtual spacecraft that is separated approximately seven heliographic degrees from the position of Earth, we note that the centre of the magnetic cloud is missing Earth and a considerably larger magnetic field strength can be found when shifting to that location. For the second run, launching four Cone CMEs and one LFFS CME, we notice that the simulated magnetised CME is arriving at the same time as in the corresponding full Cone model run. We find that to achieve this, the speed of the CME needs to be reduced in order to compensate for the expansion of the CME due to the addition of the magnetic field inside the CME. The reduced initial speed of the CME and the added magnetic field structure give rise to a very similar propagation of the CME with approximately the same arrival time at 1 au. In contrast to the Cone model, however, the magnetised CME is able to predict the magnetic field components at Earth. However, due to the interaction between the Cone model CMEs and the magnetised CME, the magnetic field amplitude is significantly lower than for the run using a single magnetised CME. Conclusions. We have presented the LFFS model that is able to simulate and predict the magnetic field components and the propagation of magnetised CMEs in the inner heliosphere and at Earth. We note that shifting towards a virtual spacecraft in the neighbourhood of Earth can give rise to much stronger magnetic field components. This gives the option of adding a grid of virtual spacecrafts to give a range of values for the magnetic field components.
  • Asvestari, Eleanna; Rindlisbacher, Tobias; Pomoell, Jens; Kilpua, Emilia (2022)
    Spheromak-type flux ropes are increasingly used for modeling coronal mass ejections (CMEs). Many models aim at accurately reconstructing the magnetic field topology of CMEs, considering its importance in assessing their impact on modern technology and human activities in space and on the ground. However, so far there is little discussion about how the details of the magnetic structure of a spheromak affect its evolution through the ambient field in the modeling domain and what impact this has on the accuracy of magnetic field topology predictions. If the spheromak has its axis of symmetry (geometric axis) at an angle with respect to the direction of the ambient field, then the spheromak starts rotating so that its symmetry axis finally aligns with the ambient field. When using the spheromak in space weather forecasting models, this tilting can happen already during insertion and significantly affects the results. In this paper, we highlight this issue previously not examined in the field of space weather and we estimate the angle by which the spheromak rotates under different conditions. To do this, we generated simple purely radial ambient magnetic field topologies (weak/strong, positive/negative) and inserted spheromaks with varying initial speed, tilt, and magnetic helicity sign. We employ different physical and geometric criteria to locate the magnetic center of mass and axis of symmetry of the spheromak. We confirm that spheromaks rotate in all investigated conditions and their direction and angle of rotation depend on the spheromak's initial properties and ambient magnetic field strength and orientation.