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Time evolution of flare-/CME-related parameters, in comparison to the deduced CME kinematics. a) Distance-, b) velocity-and acceleration-time profile of the CME. c) Reconnected magnetic flux deduced from dimming pixels (211Å211Å) and d) from flare ribbon pixels covering areas of positive (blue) and negative (red) magnetic polarity. Local reconnection rate deduced along different directions of ribbon motion, normal to the local polarity inversion line, from the e) Northern and f) Southern flare ribbon. g) GOES soft X-ray flux (black) and its time derivative (green). Yellow vertical dashed lines mark distinct times within the flare process, including the nominal flare start, peak ("MAX"), and end time. Gray vertical dashed lines mark different phases during the filament eruption.
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... From this model, we derive a 3D height and speed that should represent the true height and speed within the limitations of the idealised model assumptions. A number of researchers have used this GCS model in analysing the Earthdirected CMEs Temmer et al., 2017Suresh, Gopalswamy, and Shanmugaraju, 2022). We also consider the time period of data availability of the Atmospheric Imaging Assembly (AIA: Lemen et al., 2012) EUV telescope onboard the Solar Dynamics Observatory (SDO: Pesnell, Thompson, and Chamberlin, 2012) to observe and analyse CME low coronal signatures (Hudson and Cliver, 2001) and CHs at high resolution. ...
We investigate the deflection and rotation behaviour of 49 Earth-directed coronal mass ejections (CMEs) spanning the period from 2010 to 2020 aiming to understand the potential influence of coronal holes (CHs) on their trajectories. Our analysis incorporates data from coronagraphic observations captured from multiple vantage points, as well as extreme ultraviolet (EUV) observations utilised to identify associated coronal signatures such as solar flares and filament eruptions. For each CME, we perform a 3D reconstruction using the Graduated Cylindrical Shell (GCS) model. We perform the GCS reconstruction in multiple time steps, from the time at which the CME enters the field of view (FOV) of the coronagraphs to the time it exits. We analyse the difference in the longitude, latitude, and inclination between the first and last GCS reconstructions as possible signatures of deflection/rotation. Furthermore, we examine the presence of nearby CHs at the time of eruption and employ the Collection of Analysis Tools for Coronal Holes (CATCH) to estimate relevant CH parameters, including magnetic-field strength, centre of mass, and area. To assess the potential influence of CHs on the deflection and rotation of CMEs, we calculate the Coronal Hole Influence Parameter (CHIP) for each event and analyse its relationship with their trajectories. A statistically significant difference is observed between CHIP force and the overall change in a CME’s direction in the lower corona. The overall change in a CME’s direction accounts cumulatively for the change in latitude, longitude, and rotation. This suggests that the CHIP force in the low corona has a significant influence on the overall change in the direction of Earth-directed CMEs. However, as the CME evolves outward, the CHIP force becomes less effective in causing deflection or rotation at greater distances. Additionally, we observe a negative correlation between the deflection rate of the CMEs and their velocity, suggesting that higher velocities are associated with lower deflection rates. Hence, the velocity of a CME, along with the magnetic field from CHs, appears to play a significant role in the deflection of CMEs. By conducting this comprehensive analysis, we aim to enhance our understanding of the complex interplay between CHs, CME trajectories, and relevant factors such as velocity and magnetic-field strength.
Based on the new mechanism, the Forbush decrease characteristics are calculated for eight magnetic cloud types. It is shown that the Forbush decrease amplitude does not depend on the magnetic cloud type, while the anisotropy strongly does. The Forbush decrease spectrum for (2–150 GV) rigidities is calculated for the first time. The Forbush decrease amplitude for low rigidities is ∼100%, which can be explained by a large number of forbidden particle trajectories. The Forbush decrease amplitude rapidly decreases for high rigidities due to the geometric condition. Comparing the calculated Forbush decrease characteristics with measurements for two events shows that the Forbush decrease amplitudes agree with the measurements quantitatively, and the anisotropies do qualitatively.
Coronal Mass Ejections (CMEs) are the key drivers of strong to extreme space weather storms at the Earth that can have drastic consequences for technological systems in space and on ground. The ability of a CME to drive geomagnetic disturbances depends crucially on the magnetic structure of the embedded flux rope, which is thus essential to predict. The current capabilities in forecasting in advance (at least half a day before) the geoeffectiveness of a given CME is however severely hampered by the lack of remote-sensing measurements of the magnetic field in the corona and adequate tools to predict how CMEs deform, rotate, and deflect during their travel through the coronal and interplanetary space as they interact with the ambient solar wind and other CMEs. These problems can lead not only to overestimation or underestimation of the severity of a storm, but also to forecasting “misses” and “false alarms” that are particularly difficult for the end-users. In this paper, we discuss the current status and future challenges and prospects related to forecasting of the magnetic structure and orientation of CMEs. We focus both on observational- and modeling-based (first principle and semiempirical) approaches and discuss the space- and ground-based observations that would be the most optimal for making accurate space weather predictions. We also cover the gaps in our current understanding related to the formation and eruption of the CME flux rope and physical processes that govern its evolution in the variable ambient solar wind background that complicate the forecasting.
Coronal mass ejections (CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere into the solar wind. When these high-speed magnetized plasmas along with the energetic particles arrive at the Earth, they may interact with the magnetosphere and ionosphere, and seriously affect the safety of human high-tech activities in outer space. The travel time of a CME to 1 AU is about 1–3 days, while energetic particles from the eruptions arrive even earlier. An efficient forecast of these phenomena therefore requires a clear detection of CMEs/flares at the stage as early as possible. To estimate the possibility of an eruption leading to a CME/flare, we need to elucidate some fundamental but elusive processes including in particular the origin and structures of CMEs/flares. Understanding these processes can not only improve the prediction of the occurrence of CMEs/flares and their effects on geospace and the heliosphere but also help understand the mass ejections and flares on other solar-type stars. The main purpose of this review is to address the origin and early structures of CMEs/flares, from multi-wavelength observational perspective. First of all, we start with the ongoing debate of whether the pre-eruptive configuration, i.e., a helical magnetic flux rope (MFR), of CMEs/flares exists before the eruption and then emphatically introduce observational manifestations of the MFR. Secondly, we elaborate on the possible formation mechanisms of the MFR through distinct ways. Thirdly, we discuss the initiation of the MFR and associated dynamics during its evolution toward the CME/flare. Finally, we come to some conclusions and put forward some prospects in the future.
