Tibor Torok

The magnetic fields that make up the internal structure of coronal mass ejections (CMEs) are thought to be organized in a flux rope configuration, consisting of twisted magnetic fields that wind about a central axis. Remote-sensing observations of CMEs show a wide range of morphologies, dynamics, and evolution, including rotation, nonuniform expansion, deflection, and interaction with the ambient solar wind. In situ measurements, however, typically consist of a single 1D spacecraft trajectory through a large 3D structure (or a few at best), restricting our ability to determine how CME magnetic structure varies in space and time. In this work, we analyze the magnetic configuration of two idealized CMEs during their early evolution in the range of 1–30 R _⊙ using the Magnetohydrodynamic Algorithm Outside a Sphere code. The initial flux ropes differ only in their orientation with respect to the global dipole and erupt from a bipolar active region below the streamer belt in a simplified coronal environment. We deploy a fleet of synthetic spacecraft throughout the CMEs’ paths at different combinations of latitudes, longitudes, and heliocentric distances. We identify and examine flux rope signatures in the synthetic in situ profiles to characterize radial variations as well as latitudinal/longitudinal ones. We find that, even in a simplified CME erupting under solar minimum–like conditions, the sampling location significantly affects the global structure that would be deduced from common flux rope reconstruction and analysis techniques used for in situ measurements. Additionally, we consider possible in situ signatures that may serve as indicators of the source region’s topology.

We study the relationship between the speed of coronal mass ejections (CMEs) and the height profile of the ambient magnetic field, quantified by its decay index, n ( h ). Our sample is composed of 15 very fast CMEs ( V _CME ≥ 1500 kms ^–1 ; all halo CMEs) and 22 halo CMEs below this speed limit from Solar Cycle 23. The very fast CMEs yield a high correlation of 0.81 between V _CME and the slope of n ( h ) in a height range above the onset height of the torus instability if one extremely fast outlier, which closely followed another very fast CME, is excluded. This is consistent with the hypothesis that the torus instability plays a decisive role in CME acceleration. The whole sample yields a weaker correlation, which is still significant if events with a broad torus-stable dip in n ( h ) are excluded. A parametric simulation study of flux-rope eruptions from quadrupolar and two-scale bipolar source regions confirms the decelerating effect of such dips. Very fast, moderate-velocity, and confined eruptions are found.

The energy source for major solar eruptions, such as flares and coronal mass ejections (CMEs), is recognized to be the free magnetic energy (energy above the potential field state) stored in the solar magnetic field prior to eruption. A key question for both predicting future eruptions and estimating their possible magnitude is, what is the bound to this energy?The Aly-Sturrock theorem states that the energy of a fully force-free field cannot exceed the energy of the so-called open field. If the theorem holds, this places an upper limit on the amount of free energy that can be stored. This is not a practical limit, as even the largest CMEs open only a portion of the coronal magnetic field. The energy of a closely related field, the partially open field (POF), is believed to provide the corresponding limit for a localized region, such as an active region. We have developed practical methods for estimating the POF energy (POFE). The estimates are based on potential-field like solves that can be computed rapidly. We test our estimation methods by comparing them with the maximum energy storage achieved in MHD simulations of three solar eruptions: July 14, 2000, October 1, 2011, and March 7, 2012. We discuss the practicality of applying POFE estimates routinely to solar active regions. Research supported by NASA and NSF.

Large-scale solar eruptions, which are observed as flares, erupting prominences/filaments, and coronal mass ejections (CMEs), are powered by the free (excess) magnetic energy that is stored prior to eruption in current-carrying (sheared/twisted) magnetic fields. During an eruption, some of this magnetic energy is released and converted into kinetic energy in the form of thermal/non-thermal particle energy and bulk flow energy. It is well established that magnetic reconnection is the key driver of this energy release and conversion. However, the detailed physical conditions that determine the partitioning and distribution of the released energy are not yet well understood. Following the seminal work by Birn et al. (2009), we employ magnetohydrodynamic (MHD) simulations to study the energy conversion and transport due to reconnection in a flare current sheet, using an adiabatic energy equation. We extend the work by Birn et al. in three different ways. First, we consider a model in which the flare current layer is self-consistently formed by the eruption of a magnetic flux rope that evolves into a CME. Second, we incorporate the effect of reconnection between the legs of the flux rope. Third, we extend the analysis of the energy transport (and plasma heating) to the CME. In this presentation we summarize our main results and briefly discuss the next step, which will be the extension of our model to thermodynamic MHD.

We generalize a magnetogram-matching Biot–Savart law (BSl) from planar to spherical geometry. For a given coronal current density J , this law determines the magnetic field B ˜ whose radial component vanishes at the surface. The superposition of B ˜ with a potential field defined by a given surface radial field, B _r , provides the entire configuration where B _r remains unchanged by the currents. Using this approach, we (1) upgrade our regularized BSls for constructing coronal magnetic flux ropes (MFRs) and (2) propose a new method for decomposing a measured photospheric magnetic field as B = B pot + B T + B S ˜ , where the potential, B _pot, toroidal, B _T , and poloidal, B S ˜ , fields are determined by B _r , J _r , and the surface divergence of B – B _pot, respectively, all derived from magnetic data. Our B _T is identical to the one in the alternative Gaussian decomposition by P. W. Schuck et al., while B _pot and B S ˜ are different from their poloidal fields B P < and B P > , which are potential in the infinitesimal proximity to the upper and lower side of the surface, respectively. In contrast, our B S ˜ has no such constraints and, as B _pot and B _T , refers to the same upper side of the surface. In spite of these differences, for a continuous J distribution across the surface, B _pot and B S ˜ are linear combinations of B P < and B P > . We demonstrate that, similar to the Gaussian method, our decomposition allows one to identify the footprints and projected surface-location of MFRs in the solar corona, as well as the direction and connectivity of their currents.

The Sun’s corona is its tenuous outer atmosphere of hot plasma, which is difficult to observe. Most models of the corona extrapolate its magnetic field from that measured on the photosphere (the Sun’s optical surface) over a full 27-day solar rotational period, providing a time-stationary approximation. We present a model of the corona that evolves continuously in time, by assimilating photospheric magnetic field observations as they become available. This approach reproduces dynamical features that do not appear in time-stationary models. We used the model to predict coronal structure during the total solar eclipse of 8 April 2024 near the maximum of the solar activity cycle. There is better agreement between the model predictions and eclipse observations in coronal regions located above recently assimilated photospheric data.

The spectra of coronal mass ejections (CMEs) in the low corona play a crucial role in understanding their origins and physical mechanisms and enhancing space weather forecasting. However, capturing these spectra faces significant challenges. This paper introduces a scheme of a multislit spectrometer design with five slits, acquiring the global spectra of the solar corona simultaneously with a focus on the spectra of CMEs in the low corona. The chosen wavelength range of the spectrometer (170–180 Å) includes four extreme ultraviolet emission lines (Fe x 174.53 Å, Fe ix 171.07 Å, Fe x 175.26 Å, Fe x 177.24 Å), which provides information on the plasma velocity, density, and temperature. Utilizing a numerical simulation of the global corona for both the on-disk and the off-limb scenarios, we focus on resolving the ambiguity associated with various Doppler velocity components of CMEs, particularly for a fast CME in the low corona. A new application of our decomposition technique is adopted, enabling the successful identification of multiple discrete CME velocity components. Our findings demonstrate a strong correlation between the synthetic model spectra and the inverted results, indicating the robustness of our decomposition method and its significant potential for global monitoring of the solar corona, including CMEs.

The spectra of coronal mass ejections (CMEs) in the low corona play a crucial role in understanding their origins and physical mechanism, and enhancing space weather forecasting. However, capturing these spectra faces significant challenges. This paper introduces a scheme of a multi-slit spectrometer design with five slits, acquiring the global spectra of the solar corona simultaneously with a focus on the spectra of CMEs in the low corona. The chosen wavelength range of the spectrometer (170-180 Å) includes four extreme ultraviolet emission lines (Fe x 174.53 Å, Fe ix 171.07 Å, Fe x 175.26 Å, Fe x 177.24 Å), which provides information of plasma velocity, density and temperature. Utilizing a numerical simulation of the global corona for both the on-disk and the off-limb scenarios, we focus on resolving the ambiguity associated with various Doppler velocity components of CMEs, particularly for a fast CME in the low corona. A new application of our decomposition technique is adopted, enabling the successful identification of multiple discrete CME velocity components. Our findings demonstrate a strong correlation between the synthetic model spectra and the inverted results, indicating the robustness of our decomposition method and its significant potential for global monitoring of the solar corona, including CMEs.

Many proxies for assessing the eruptive activity of solar active regions (ARs) have been suggested, mostly based on measurements of the photospheric magnetic field. Here we test the usefulness of DC/RC (ratio of photospheric direct to return current) for assessing the ability of ARs to produce CMEs, and compare it with the amount of shear along the eruptive section of the polarity inversion line (PIL). We find that all source regions of eruptive flares have DC/RC > 1.63 and PIL shear > 45° (3.2 and 68° on average), tending to be larger for stronger events. Both quantities are on average smaller for source regions of confined flares (2.2 and 46°), albeit with substantial overlap. Many source regions, especially those of eruptive X-class flares, exhibit elongated direct currents (EDCs) bracketing the eruptive PIL segment, typically coinciding with areas of continuous PIL shear > 45°. However, a small subset of confined flares have DC/RC close to unity, very low PIL shear (< 38°), and no clear EDC signatures, rendering such regions less likely to produce a CME. A simple quantitative analysis reveals that DC/RC and PIL shear are almost equally good proxies for assessing CME-productivity, and comparable to other proxies suggested in the literature. We also demonstrate that an inadequate selection of the current-integration area typically yields a substantial underestimation of DC/RC.

NASA's Community Coordinated Modeling Center (CCMC) presents CORHEL-CME, our newest addition to the Runs-On-Request system in the solar and heliospheric modeling domain. CORHEL-CME, developed by Predictive Science Inc., is a highly automated and interactive MHD modeling framework designed to simulate multiple coronal mass ejections within a realistic coronal and heliospheric environment. It combines three key innovations:1. Interactive design of CMEs using a GUI-based web interfaceCORHEL-CME's user interface is designed for non-experts. It offers real-time diagnostics to assist with model settings, guides users through creating full physics-based CME simulations, and provides web-based visualization reports.2. Modeling CMEs originating from complex active regionsCORHEL-CME includes a flux rope model called RBSL (Titov et al., 2018), allowing users to create pre-eruptive flux rope configurations above elongated and curved polarity inversion lines. This feature enables users to realistically simulate CMEs originating from complex active regions.3. Efficient, full physics-based simulations of CMEsUsing the web interface, the users set up simulation runs, including a simplified (zero-beta) MHD model of multiple flux ropes, a quasi-steady-state coronal MHD background model, and a high-fidelity time-dependent CME simulation. All simulation runs are performed on AWS high-performance GPU servers maintained by the CCMC.In this presentation, we will showcase the usage of CORHEL-CME via CCMC's Runs-On-Request system and show an example run based on an event from March 7th, 2012. The new framework is publicly accessible through the CCMC website.