Ranadeep Sarkar

Accurate prediction of the magnetic structure of interplanetary coronal mass ejections (ICMEs) remains a key challenge in space weather forecasting. Despite several efforts using global MHD modeling, it remains difficult to deduce a flux-rope solution that can accurately and reliably reproduce the magnetic structure of a CME. We present the Flux Rope embedded in the Solar Magnetic Field (FROST), a new flux-rope model implementation within the European Heliospheric Forecast Information Asset (EUHFORIA), featuring an initially force-free toroidal flux rope embedded in the low-coronal magnetic field. FROST employs a novel embedding technique that self-consistently generates a draping magnetic field around the flux rope, ensuring continuity of the normal magnetic field component at the CME boundary. The dynamics of the flux rope in the low and middle corona is solved by a nonuniform advection constrained by the observed kinematics of the event. This results in a global, nontoroidal, stretched loop-like magnetic structure. At heliospheric distances, the evolution is modeled as an MHD process using EUHFORIA. We validate the FROST model implementation by simulating the CME event of 2013 April 11 and comparing the results with in situ magnetic field measurements at 1 au. The modeled magnetic field profiles of the flux rope exhibit strong agreement with the observations, with correlation coefficients ranging from 0.64–0.93 for B _x , 0.92–0.95 for B _y , and 0.82–0.87 for B _z component of the magnetic field. These results demonstrate the capability of the proposed flux-rope model to significantly improve ICME magnetic field prediction, highlighting its strong potential for advancing space-weather forecasting capabilities.

While flare-associated coronal mass ejections (CMEs) generally show a strong association between flare X-ray flux and CME kinematics, their volumetric evolution and its link to both kinematics and flare activity remain less explored. In this study, we investigate the volumetric and kinematic coevolution of 10 Earth-directed, flare-associated CMEs using multiviewpoint observations from Solar TErrestrial RElations Observatory (STEREO)-A, STEREO-B, and SOlar and Heliospheric Observatory. We perform 3D reconstructions of the CME flux ropes with the graduated cylindrical shell model and derive their geometrical parameters. We find that the total CME volume follows a power-law dependence on the leading edge height and that different structural components expand at different rates, with the ellipsoidal front expanding faster than the conical legs. Furthermore, the volumetric evolution follows a multiphase pattern: initial overexpansion, a gradual reduction in the expansion rate, and finally saturation at a higher heliocentric distance. This is similar to the well-established three-phase evolution of the CME kinematics. Notably, the second-order derivative of volume with time shows a strong temporal correlation with both CME acceleration and the GOES soft X-ray flux of the associated flare. This is the first study to report such a correspondence between volumetric evolution and flare timing, highlighting the role of flare energy release in governing CME expansion dynamics. Our findings motivate further studies into the coupling between magnetic reconnection and CME volumetric evolution in the corona.

Coronal mass ejections (CMEs) are powerful drivers of space weather, with magnetic flux ropes (MFRs) widely regarded as their primary precursors. However, the variation in the reconnection (RC) flux during the evolution of MFRs during CME eruptions remains poorly understood. In this paper, we develop a 3D magnetohydrodynamic (MHD) model that we use to explore the temporal evolution of the RC flux during the MFR evolution using both numerical simulations and observational data. Our initial coronal configuration features an isothermal atmosphere and a potential arcade magnetic field beneath which an MFR emerges at the lower boundary. As the MFR rises, we observe significant stretching and compression of the overlying magnetic field beneath it. Magnetic RC begins with the gradual formation of a current sheet, eventually culminating with the impulsive expulsion of the flux rope. We analyze the temporal evolution of RC fluxes during two successive MFR eruptions while continuously emerging the twisted flux rope through the lower boundary. We also conduct a similar analysis using observational data from the Helioseismic and Magnetic Imager and the Atmospheric Imaging Assembly for an eruptive event. Comparing our MHD simulation with observational data, we find that RC flux play a crucial role in the determination of CME kinematics. From the onset to the eruption, the rate of RC shows a monotonic variation with the acceleration. This simulation of a solar eruption provides important insights into the complex dynamics of CME initiation and progression.

One of the major challenges in space weather forecasting is the reliable prediction of the magnetic structure of interplanetary coronal mass ejections (ICMEs) in near-Earth space. This challenge becomes even more pronounced when a CME interacts with high-speed streams (HSSs) or other CMEs during its interplanetary evolution. Within the framework of global MHD modeling, several efforts have been made to simulate the CME magnetic field from the Sun to Earth. However, it remains difficult to deduce a flux-rope solution that can robustly reproduce the magnetic structure of CMEs. Moreover, a comprehensive understanding of how CME–HSS interactions lead to enhanced space weather impacts of CMEs and their associated sheath regions is still lacking.In this work, we implement a new flux-rope model in the European Heliospheric Forecast Information Asset (EUHFORIA), featuring an initially force-free toroidal flux rope embedded in the low-coronal magnetic field. The novel embedding technique self-consistently generates a draping field around the flux rope, preserving the normal component of the magnetic field at the flux-rope boundary. The flux-rope dynamics in the low and middle corona are solved using a non-uniform advection constrained by the observed kinematics of the CME. This produces a global, non-toroidal, stretched loop-like magnetic structure, in which the lower half of the torus remains below the inner boundary of the heliospheric model. At heliospheric distances, the subsequent evolution is modeled as an MHD process using EUHFORIA, yielding a classical flux-rope geometry consistent with observations of bi-directional electrons.We further investigate CME–HSS interactions using this modeling framework by constructing synthetic high-speed streams and studying their interaction with CMEs of varying kinematics. Our results show that CME–HSS interactions lead to significant deformation of the CME magnetic structure. We find that the relative speed between the CME and the HSS plays a decisive role in determining the degree of ICME compression and the resulting enhancement of its space weather impact.

One of the major challenges in space weather forecasting is to reliably predict the magnetic structure of interplanetary coronal mass ejections (ICMEs) in the near-Earth space. In the framework of global MHD modelling, several efforts have been made to model the CME magnetic field from Sun to Earth. However, it remains challenging to deduce a flux-rope solution that can reliably model the magnetic structure of a CME. Aiming to improve the space-weather forecasting capability, we implement a new flux-rope model in “European heliospheric forecasting information asset” (EUHFORIA). Our flux-rope model includes an initially force-free toroidal flux-rope that is embedded in the low-coronal magnetic field. The embedding technique adds a significant novelty to the state-of-the-art as it preserves the continuity condition of the magnetic field at the flux-rope boundary and maintains the force-free solution of the flux rope. The dynamics of the flux rope in the low and middle corona are solved by a non-uniform advection constrained by the observed kinematics of the event. This results in a global non-toroidal loop-like magnetic structure that locally manifests as a cylindrical structure. At heliospheric distances, the evolution is modeled as a MHD process using EUHFORIA. We assess our model results on several ICMEs, including cases of interacting events. Comparing the model results with the in-situ magnetic field configuration of the ICME at 1 au, we find that the simulated magnetic field profiles of the flux-rope are in very good agreement with the in-situ observations. Therefore, the framework of toroidal model implementation as developed in this study could prove to be a major step-forward in forecasting the geo-effectiveness of CMEs.

One of the major challenges in space weather forecasting is to reliably predict the magnetic structure of interplanetary coronal mass ejections (ICMEs) in the near-Earth space. In the framework of global MHD modelling, several efforts have been made to model the CME magnetic field from Sun to Earth. However, it remains challenging to deduce a flux-rope solution that can reliably model the magnetic structure of a CME. Spheromaks are one of the models that are widely used to characterize the internal magnetic structure of a CME. However, recent studies show that spheromaks are prone to experience a large rotation when injected in the heliospheric domain which may affect the prediction efficacy of CME magnetic fields at 1 AU. Moreover, the fully inserted spheromaks do not have any legs attached to the Sun. In addition, due to the inherent topology of the spheromak, the in-situ signature may exhibit a double flux-rope-like profile not reproduced by standard locally cylindrical flux rope models. Aiming to study the dynamics of CMEs exhibiting different magnetic topologies, we implement a new flux-rope model in “European heliospheric forecasting information asset” (EUHFORIA). Our flux-rope model includes an initially force-free toroidal flux-rope that is embedded in the low-coronal magnetic field. The dynamics of the flux rope in the low and middle corona is solved by a non-uniform advection constrained by the observed kinematics of the event. This results in a global non-toroidal loop-like magnetic structure that locally manifests as a cylindrical structure. At heliospheric distances, the evolution is modeled as a MHD process using EUHFORIA. As proof of concept, we use this tool to two CME events. Comparing the model results with the in-situ magnetic field configuration of the ICME at 1 au, we find that the simulated magnetic field profiles of the flux-rope are in very good agreement with the in-situ observations. Therefore, the framework of toroidal model implementation as developed in this study could prove to be a major step-forward in forecasting the geo-effectiveness of CMEs.

To improve our understanding of how space weather affects our near-Earth space environment, magnetic field modelling of solar eruptive structures is essential. In particular, modelling flux ropes in a time-dependent manner to investigate their destabilization in the low corona as well as their morphological evolution and propagation can yield important information about the eruption's impact at Earth. However, finding and tracking the magnetic field lines that pertain to the flux rope in simulation data is a non-trivial task. Therefore, we developed a methodology to extract and track flux ropes in a semi-automatic way, using a combination of some flux rope proxies (like the twist parameter) and mathematical morphology algorithms. This procedure is also wrapped into a graphical user interface (GUI) to increase the user-friendliness of the methodology. We subsequently apply this methodology to time-dependent magnetofrictional method (TMFM) simulations of active regions AR12473 and AR11176. For the former, we chose to simulate a time window which featured an eruption, while for the latter, we model the active region at a time where there was only mild activity. We then analyse the propagation of the flux ropes through the low corona. We find that the eruptive flux rope of AR12473 clearly shows significant changes in the propagation direction with deflection angles peaking at 60 degrees. The AR11176 flux rope appears to be more stable, but still features non-negligible deflections peaking at about 40 degrees.

Solar flares are known to leave imprints on the magnetic field at the photosphere, often manifested as an abrupt and permanent change in the downward-directed Lorentz force in localized areas inside the active region. Our study aims to differentiate eruptive and confined solar flares based on the vertical Lorentz force variations. We select 26 eruptive and 11 confined major solar flares (stronger than the GOES M5 class) observed during 2011-2017. We analyze these flaring regions using SHARP vector-magnetograms obtained from the NASA's Helioseismic and Magnetic Imager (HMI). We also compare data corresponding to 2 synthetic flares from a delta sunspot simulation reported in Chatterjee et al. We estimate the change in the horizontal magnetic field and the total Lorentz force integrated over an area around the polarity inversion line (PIL) that encompasses the location of the flare. Our results indicate a rapid increase of the horizontal magnetic field along the flaring PIL, accompanied by a significant change in the downward-directed Lorentz force in the same vicinity. Notably, we find that all the confined events under study exhibit a total change in Lorentz force of < 1.8 x 10^22 dyne. This threshold plays an important factor in effectively distinguishing eruptive and confined flares. Further, our analysis suggests that the change in total Lorentz force also depends on the reconnection height in the solar corona during the associated flare onset. The results provide significant implications for understanding the flare-related upward impulse transmission for the associated coronal mass ejection.

The INterplanetary Flux ROpe Simulator (INFROS) is an observationally constrained analytical model dedicated to forecasting the strength of the southward component (Bz) of the magnetic field embedded in interplanetary coronal mass ejections (ICMEs). In this work, we validate the model for six ICMEs sequentially observed by two radially aligned spacecraft positioned at different heliocentric distances. The six selected ICMEs in this study comprise cases associated with isolated coronal mass ejection (CME) evolution as well as those interacting with high-speed streams (HSSs) and high-density streams (HDSs). For the isolated CMEs, our results show that the model outputs at both spacecraft are in good agreement with in situ observations. However, for most of the interacting events, the model correctly captures the CME evolution only at the inner spacecraft. Due to the interaction with HSSs and HDSs, which in most cases occurred at heliocentric distances beyond the inner spacecraft, the ICME evolution no longer remains self-similar. Consequently, the model underestimates the field strength at the outer spacecraft. Our findings indicate that constraining the INFROS model with inner-spacecraft observations significantly enhances the prediction accuracy at the outer spacecraft for the three events undergoing self-similar expansion, achieving a 90% correlation between observed and predicted Bz profiles. This work also presents a quantitative estimation of the ICME magnetic field enhancement due to interaction which may lead to severe space weather. We conclude that the assumption of self-similar expansion provides a lower limit to the magnetic field strength estimated at any heliocentric distance, based on the remote-sensing observations.