Quantifying CME arrival time uncertainty with mega ensembles

The current progression toward solar maximum provides a unique opportunity to use multi-perspective spacecraft observations together with numerical models to better understand the evolution and propagation of coronal mass ejections (CMEs). Of interest to both the scientific and forecasting communities are the Earth-directed “halo” CMEs, since they typically produce the most geoeffective events. However, determining the actual initial geometries of halo CMEs is a challenge due to the plane-of-sky projection effects. Thus the recent 15 February 2011 halo CME event has been selected for this study. During this event the Solar TErrestrial RElations Observatory (STEREO) A and B spacecraft were fortuitously located ∼ 90° away from the Sun–Earth line such that the CME was viewed as a limb event from these two spacecraft, thereby providing a more reliable constraint on the initial CME geometry. These multi-perspective observations were utilized to provide a simple geometrical description that assumes a cone shape for a CME to calculate its angular width and central position. The event was simulated using the coupled Wang–Sheeley–Arge (WSA)-Enlil 3D numerical solar corona-solar wind model. Daily updated global photospheric magnetic field maps were used to drive the background solar wind. To improve our modeling techniques, the sensitivity of the modeled CME arrival times to the initial input CME geometry was assessed by creating an ensemble of numerical simulations based on multiple sets of cone parameters for this event. It was found that the accuracy of the modeled arrival times not only depends on the initial input CME geometry, but also on the accuracy of the modeled solar wind background, which is driven by the input maps of the photospheric field. To improve the modeling of the background solar wind, the recently developed data-assimilated magnetic field synoptic maps produced by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model were used. The ADAPT maps provide a more instantaneous snapshot of the global photospheric field distribution than that provided by traditional daily updated synoptic maps. Using ADAPT to drive the background solar wind, an ensemble set of eight different CME arrival times was generated, where the spread in the predictions was ∼ 13 hours and was nearly centered on the observed CME shock arrival time.

Observations of interplanetary scintillation (IPS) provide a set of data that is used in estimating the solar wind parameters with reasonably good accuracy. Various tomography techniques have been developed to deconvolve the line‐of‐sight integration effects ingrained in observations of IPS to improve the accuracy of solar wind reconstructions. Among those, the time‐dependent tomography developed at the University of California, San Diego (UCSD) is well known for its remarkable accuracy in reproducing the solar wind speed and density at Earth by iteratively fitting a kinematic solar wind model to observations of IPS and near‐Earth spacecraft measurements. However, the kinematic model gradually breaks down as the distance from the Sun increases beyond the orbit of Earth. Therefore, it would be appropriate to use a more sophisticated model, such as a magnetohydrodynamics (MHD) model, to extend the kinematic solar wind reconstruction beyond the Earth's orbit and to the outer heliosphere. To test the suitability of this approach, we use boundary conditions provided by the UCSD time‐dependent tomography to propagate the solar wind outward in a MHD model and compare the simulation results with in situ measurements and also with the corresponding kinematic solution. Interestingly, we find notable differences in proton radial velocity and number density at Earth and various locations in the inner heliosphere between the MHD results and both the in situ data and the kinematic solution. For example, at 1 AU, the MHD velocities are generally larger than the spacecraft data by up to 150 km s−1, and the amplitude of density fluctuations is also markedly larger in the MHD solution. We show that the MHD model can deliver more reasonable results at Earth with an ad hoc adjustment of the inner boundary values. However, we conclude that the MHD model using the inner boundary conditions derived from kinematic simulations has little chance to match IPS and in situ data as well as the kinematic model does unless it too is iteratively fit to the observational data and measurements.

Context . As an unmagnetized planet, Venus lacks an intrinsic magnetic field, leading to the direct interaction with the solar wind, which results in differences in physical processes within its magnetosphere–ionosphere (MI) system compared to Earth. With intense solar wind disturbances, it has been suggested that interplanetary coronal mass ejections (ICMEs) have a pronounced effect on Venus. Aims . This study aims to investigate the responses of the Venusian plasma environment to ICMEs. A simulation driven by a real ICME event that occurred on 5 November 2011, was conducted to systematically and quantitatively analyze the plasma processes in Venusian magnetosphere. During this event, the solar wind dynamic pressure at the model input increased by a factor of up to 4.8, while the interplanetary magnetic field (IMF) strength was enhanced by a factor of 1.9. Methods . The numerical simulation for Venusian plasma environment uses a multi-fluid global magnetohydrodynamics (MHD) model, coupled with the uniform neutral atmosphere. Utilizing the upstream magnetic field data from VEX and idealized solar wind plasma parameters as model inputs, we examine the response of Venusian plasma environment after the ICME arrival. Results . Venusian plasma environment and boundaries respond rapidly on the order of minutes. During the ICME, the subsolar bow shock location exhibits an inverse-linear proportionality to the fast magnetosonic Mach number. Meanwhile, the variation in boundaries’ locations demonstrates that high solar wind dynamic pressure and an enhanced IMF display compressive and expanding effects, respectively. The total integral of the ions’ escape rate shows that under ICME passage, the O + escape rate of Venus exhibits a sustained increase, from 6.0 × 10 24 s −1 to 3.0 × 10 25 s −1 . Both solar wind dynamic pressure and IMF strength enhance ion escape, with dynamic pressure dominating this process. Conclusions . The simulation driven by a real ICME event demonstrates severe, rapid, and complex responses of Venusian plasma environments, accompanied by an order-of-magnitude enhancement O + escape rate. These results could advance the understanding of the long-term evolution of terrestrial planets and provides references for the scientific targets of future missions.

In our previous paper we reported the results of modeling of 14 selected well‐observed strong halo coronal mass ejection (CME) events using the WSA‐ENLIL cone model combination. Cone model input parameters were obtained from white light coronagraph images of the CME events using the analytical method developed by Xie et al. (2004). This work verified that coronagraph input gives reasonably good results for the CME arrival time prediction. In contrast to Taktakishvili et al. (2009), where we started the analysis by looking for clear CME signatures in the data and then proceeded to model the interplanetary consequences at 1 AU, in the present paper we start by generating a list of observed geomagnetic storm events and then work our way back to remote solar observations and carry out the corresponding CME modeling. The approach used in this study is addressing space weather forecasting and operational needs. We analyzed 36 particularly strong geomagnetic storms, then tried to associate them with particular CMEs using SOHO/LASCO catalogue, and finally modeled these CMEs using WSA‐ENLIL cone model. Recently, Pulkkinen et al. (2010) developed a novel method for automatic determination of cone model parameters. We employed both analytical and automatic methods to determine cone model input parameters. We examined the CME arrival times and magnitude of impact at 1 AU for both techniques. The results of the simulations are compared with the ACE satellite observations. This comparison demonstrated that WSA‐ENLIL model combination with coronagraph input gives reasonably good results for the CME arrival times for this set of “geoeffective” CME events as well.

Using in situ measurements and remote-sensing observations, we study two coronal mass ejections (CMEs) that left the Sun on 2012 June 13–14 and impacted both Venus and Earth while the planets were in close radial alignment. The two CMEs generate multiple fronts in Solar Terrestrial Relations Observatory (STEREO)/Heliospheric Imager (HI) images, which can also be observed in the “J-map” as bifurcated features. We present the “ghost front” model to combine remote observations from STEREO/SECCHI and in situ observations from the Wind and Venus Express (VEX) spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the observations of multiple fronts to a kinematically evolving flux rope model and assuming the CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson scattered light returned from the flank and nose of a single front for each CME. An interaction takes place between CME-1 and CME-2 that can be observed in the HI-1 field of view (FOV) before CME-1 encounters Venus. The multipoint in situ observations of the shock–CME interaction event serve as further evidence of the interaction between CMEs. The arrival times calculated from the ghost front model are within 2.5 hr of those observed at VEX and Wind. Our analysis indicates that ghost fronts could provide information about the longitudinally extended shape of the CME in the FOV of HI-1, which can be used to improve the forecast of interplanetary CME arrival time at Earth.

Coronal mass ejections (CMEs) are the main drivers of disturbances in the solar heliosphere because they propagate and interact with the magnetic field of the solar wind. It is crucial to investigate the evolution of CMEs and their deformation for understanding the interaction between the solar wind and CMEs. We quantify the effect of the dynamic solar wind on the propagation of a CME in the heliosphere with a hydrodynamic plasma cloud-cone model and a linear force-free spheromak model at various locations in the heliosphere. We chose a CME event that launched on SOL2021-09-23T04:39:45 and was observed by multiple spacecraft, namely BepiColombo, Parker Solar Probe, Solar Orbiter, Stereo A and ACE. The solar wind was modelled in the steady and dynamic regimes in the Icarus model. The CME parameters were approximated for the selected event, and two CME models (spheromak and cone) were launched from the inner heliosphere boundary. The obtained synthetic in situ measurements were compared to the observed in situ measurements at all spacecraft. The internal magnetic field of the flux rope was better reconstructed by the spheromak model than by the cone CME model. The cone CME model maintained a nearly constant longitudinal angular extension while somewhat contracting in the radial direction. In contrast, the spheromak model contracted in the longitudinal direction while expanding in the radial direction. The CME sheath and magnetic cloud signatures were better reproduced at the four spacecraft clustered around the CME nose by the spheromak CME model. The dynamic solar wind caused a greater deceleration of the modelled CME than the steady-state solar wind solution. Because the background was homogeneous, the modelled CME properties were only mildly affected by the solar wind regime, however.

Coronal mass ejections (CMEs) are one of the main drivers of strong space weather disturbances. The interaction between CMEs and the Earth’s magnetic field can cause a wide range of phenomena and the magnetic configuration and orientation are key factors in determining the geo-effectiveness of this type of events. Modeling these events accurately is an ongoing challenge, and data-driven simulations are a valuable operational and research tool, widely used by the community.Using the 3D data-driven MagnetoHydroDynamical (MHD) heliospheric solar wind and CME evolution model EUHFORIA (European Heliospheric FORecasting Information Asset), our aim is to model CME events that can impact the Earth. Forthcoming missions, developed by ASI (Italian Space Agency), aims to improve space weather forecasting capabilities, particularly for CMEs, solar energetic particles (SEPs), and other interplanetary disturbances.In particular SEPs events are of huge importance for Space Weather risks. It is well established that particle acceleration at shocks is linked to the turbulence characterizing the environment in which particles are propagating. Consequently, understanding the role of turbulence is of fundamental importance for the propagation, acceleration and characterization of SEP events. To account for these processes, we aim to integrate the effects of both large-scale structures and turbulence in the simulations, either by using 3D EUHFORIA outputs or thorough 2.5 MHD simulation performed with MPI-ArmVAC, thereby enhancing the diagnostic capabilities of virtual spacecraft.As a case study, we analyse the event of 3 November 2021, observed by both ACE and Solar Orbiter (SolO), which were nearly co-located in latitude and longitude, with a radial separation of ~22 million km. Comparing EUHFORIA simulations with in situ data from both spacecraft provides valuable insight into the new mission’s potential performance once operational. This study was carried out within the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under Contract Grant Nos. 2024-5-E.0-CUP and I53D24000060005.

We present a qualitative and quantitative comparison of a single coronal mass ejection (CME) as observed by LASCO on 5 October 1996 with the results of a two-dimensional magnetohydrodynamic (MHD) model. This event was selected as a clear example of a CME that is not caused by the disruption of a helmet streamer. This CME occurs against the background of multiple bright streamers on the west limb. The CME is first seen as a brightening of the entire west limb. The CME has a bright, sharp front that moves outward with no significant change in shape. The CME moves outward with roughly constant velocity that is approximately twice as fast at high latitude as near the streamer. The measured CME mass is 1.2×1016 g. There are two parts to the MHD model. The pre-event corona was calculated using a 2-dimensional bi-modal model. The CME is simulated using a time dependent perturbation at the base of the corona. The model successfully reproduces the observed morphology, velocity profiles, and change in coronal mass. The observed velocity asymmetry is a natural consequence of the structure of the pre-event corona. Animations have been generated from both the data and model to illustrate the good agreement between the observations and simulation. These animations can be found on the CD-ROM which accompanies this volume.

We present study of the complex event consisting of several solar wind transients detected by Advanced Composition Explorer (ACE) on 4 -- 7 August 2011, that caused a geomagnetic storm with Dst$=-$110 nT. The supposed coronal sources -- three flares and coronal mass ejections (CMEs) occurred on 2 -- 4 August 2011 in the active region (AR) 11261. To investigate the solar origin and formation of these transients we studied kinematic and thermodynamic properties of the expanding coronal structures using the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) EUV images and the differential emission measure (DEM) diagnostics. The Helioseismic and Magnetic Imager (HMI) magnetic field maps were used as the input data for the 3D magnetohydrodynamic (MHD) model to describe the flux rope ejection. We characterize the early phase of the flux rope ejection in the corona, where the usual three-component CME structure formed. The flux rope ejected with a speed of about 200~km~s$^{-1}$ to the height of 0.25~R$_{\odot}$. The kinematics of the modeled CME front agrees well with the Solar Terrestrial Relations Observatory (STEREO) EUV measurements. Using the results of the plasma diagnostics and MHD modeling, we calculated the ion charge ratios of carbon and oxygen as well as the mean charge state of iron ions of the 2 August 2011 CME, taking into account the processes of heating, cooling, expansion, ionization, and recombination of the moving plasma in the corona up to the frozen-in region. We estimated a probable heating rate of the CME plasma in the low corona by matching the calculated ion composition parameters of the CME with those measured in situ for the solar wind transients. We also consider the similarities and discrepancies between the results of the MHD simulation and the observations.

In this study, we simulate the Solar Wind Charge Exchange (SWCX) soft X‐ray emissions at dayside magnetosheath and cusps by using magnetohydrodynamic (MHD) and LAtmos TEst Particle (LaTeP) models. MHD models are unable to resolve the particle kinetic effects, such as the different behaviors of ions with different q/m, or distinguish the magnetospheric plasma from the solar wind plasma. We investigate these effects with the LaTeP model. As the LaTeP model does not self‐compute magnetic and electric field, the magnetic and electric field data obtained from Open Geospace General Circulation Model (OpenGGCM) and Lagrangian version of the piecewise parabolic method (PPMLR) MHD model are used as the input to LaTeP model. The soft X‐ray emissivity maps simulated from pure OpenGGCM and PPMLR MHD approaches and from LaTeP‐OpenGGCM and LaTeP‐PPMLR approaches are presented and compared. The results indicate that the LaTeP model can well resolve the kinetic effects and can be used to investigate the individual spectral characteristics. Therefore, the LaTeP model is a complementary approach for simulating the X‐ray emissions near the dayside magnetopause. We also calculate the ratio of integrated OVII/OVIII line intensities, produced by charge exchange of O7+ ions and O8+ ions, respectively. We find a relatively higher ratio at the bow shock compared to the surrounding areas, suggesting that this ratio can be an effective parameter to identify the bow shock location.

Coronal mass ejections (CMEs) erupting from the host star are expected to affect the atmospheric erosion processes of planets. For planets with a magnetosphere, the embedded magnetic field in the CMEs is thought to be the most important parameter to affect planetary mass-loss. In this work, we investigate the effect of different magnetic field structures of stellar CMEs on the atmosphere of a hot Jupiter with a dipolar magnetosphere. We use a time-dependent 3D radiative magnetohydrodynamic (MHD) atmospheric escape model that self-consistently models the outflow from hot Jupiter’s magnetosphere and its interaction with stellar CMEs. For our study, we consider three configurations of magnetic field embedded in CMEs – (a) northward $B_z$ component, (b) southward $B_z$ component, and (c) radial component. We find that both the CMEs with northward $B_z$ and southward $B_z$ increase the planetary mass-loss rate when the CME arrives from the stellar side, with the mass-loss rate remaining higher for the CME with northward $B_z$ until it arrives on the opposite side. The largest magnetopause is found for the CME with a southward $B_z$ component. During the passage of a CME, the planetary magnetosphere goes through three distinct changes – (1) compressed magnetosphere, (2) enlarged magnetosphere, and (3) relaxed magnetosphere for all three CME configurations. The computed synthetic Ly $\alpha$ transit absorption generally increases when the CME is in interaction with the planet for all magnetic configurations but the maximum Ly $\alpha$ absorption is found for the case of radial CME with the most compressed magnetosphere.

During its passage through the high‐latitude heliosphere, Ulysses observed interplanetary coronal mass ejections (ICMEs) bounded by shocks. These forward‐reverse shock pairs have only been observed at high latitude in the fast solar wind. It has been suggested (e.g., Gosling et al., 1995) that these shock pairs are the result of expansion of coronal mass ejections into the ambient solar wind, so‐called “overexpansion”. Here we demonstrate an alternative explanation for forward‐reverse shock pairs by means of a three‐dimensional numerical magnetohydrodynamics (MHD) model of a CME interacting with the solar wind. Our global steady state coronal model possesses fast and slow speed solar wind at high and low latitudes, respectively, reminiscent of near solar minimum conditions. Within this model system, a CME erupts from the coronal streamer belt with an initial speed in excess of 1000 km/s, which naturally drives a forward shock into the ambient solar wind. When the CME is greater than 40 R⊙ from the Sun, we find that a reverse shock forms poleward of the CME as a result of the interaction of the CME with the solar wind. In front of the CME, the slow wind is deflected to higher latitude while behind the CME, fast wind is deflected to low latitude. These deflected streams collide to form a reverse shock. The shock pair formed in this way naturally occurs at high latitude in the fast wind as observed. We will discuss these model results in the context of in situ solar wind data.

We propose a “pileup accident” hypothesis, based on the solar wind data analysis and magnetohydrodynamics modeling, to explain unexpectedly geoeffective solar wind structure which caused the largest magnetic storm so far during the solar cycle 24 on 17 March 2015: First, a fast coronal mass ejection with strong southward magnetic fields both in the sheath and in the ejecta was followed by a high‐speed stream from a nearby coronal hole. This combination resulted in less adiabatic expansion than usual to keep the high speed, strong magnetic field, and high density within the coronal mass ejection. Second, preceding slow and high‐density solar wind was piled up ahead of the coronal mass ejection just before the arrival at the Earth to further enhance its magnetic field and density. Finally, the enhanced solar wind speed, magnetic field, and density worked all together to drive the major magnetic storm.

To study the evolution and propagation of Coronal Mass Ejections (CMEs), the advanced magnetized flux rope CME model, Flux Rope in 3D (FRi3D), has been integrated into the European Heliospheric Forecasting Information Asset (EUHFORIA). Recent updates have been addressing the computational efficiency and numerical stability issues of this CME model. In this work, the latest improvements to the FRi3D model are represented, including optimizations of the integral calculations in the ai.fri3d Python package, an updated CME leg disconnection method, and the introduction of a new datacube injection methodology for time‐efficient FRi3D simulations. Within the datacube injection method, the input values of FRi3D at the inner boundary of EUHFORIA are precomputed, eliminating the need to calculate the FRi3D CME model during the solar wind simulation with superimposed CMEs. The datacube injection method is tested by modeling the CME event of 12 July 2012, and by conducting ensemble runs for this event. The updates to the FRi3D Python package reduced the computation time to , and the datacube methodology achieved a computational time reduction of up to compared to previous FRi3D versions. Numerical stability was significantly improved, and ensemble simulations demonstrated robust ensemble spreads for the thermodynamic and magnetic time profiles on Earth. These updates enhance the efficiency, stability, and accuracy of the FRi3D model, making it highly suitable for predicting both the CME arrival time, magnetic field strength, and velocity. As a result, the advancements contribute significantly to the future operational space weather forecasting capabilities of the FRi3D CME model.

We present a three‐dimensional (3‐D) numerical ideal magnetohydrodynamics (MHD) model describing the time‐dependent expulsion of a coronal mass ejection (CME) from the solar corona propagating to 1 astronomical unit (AU). The simulations are performed using the Block Adaptive Tree Solar‐Wind Roe Upwind Scheme (BATS‐R‐US) code. We begin by developing a global steady‐state model of the corona that possesses high‐latitude coronal holes and a helmet streamer structure with a current sheet at the equator. The Archimedean spiral topology of the interplanetary magnetic field is reproduced along with fast and slow speed solar wind. Within this model system, we drive a CME to erupt by the introduction of a Gibson‐Low magnetic flux rope that is anchored at both ends in the photosphere and embedded in the helmet streamer in an initial state of force imbalance. The flux rope rapidly expands and is ejected from the corona with maximum speeds in excess of 1000 km/s. Physics‐based adaptive mesh refinement (AMR) allows us to capture the structure of the CME focused on a particular Sun‐Earth line with high spatial resolution given to the bow shock ahead of the flux rope as well as to the current sheet behind. The CME produces a large magnetic cloud at 1 AU (>100 R⊙) in which Bz undergoes a full rotation from north to south with an amplitude of 20 nT. In a companion paper, we find that the CME is very effective in generating strong geomagnetic activity at the Earth in two ways. First, through the strong sustained southward Bz (lasting more than 10 hours) and, second, by a pressure increase associated with the CME‐driven shock that compresses the magnetosphere.