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KSO Hα filtergram showing the flare before it reaches its maximum intensity. The polarity inversion line (PIL) is shown as white line, different directions (tracking paths: N1/2 for the northern part and S1/2 for the southern part) along which the ribbon main motion is tracked are shown with yellow rectangles, bright flare pixels cumulated until the time of the image shown (09:38:26 UT) are shown as blue areas (positive polarity) and red areas (negative polarity).
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... shown in Fig. 1, we derive the flare ribbon separation speed from intensity profiles calculated along rectangular slices oriented perpendicularly to the PIL along two directions within each magnetic polarity (tracking paths: N1/2, S1/2). At each time step the intensity profile of each slice is fitted with a Gaussian func- tion leading to a ...
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... rate ( Fig. 6e and f; deduced from the flare ribbon separation velocity and associated magnetic flux; cf. Sect. 2.1) is distributed in a non-uniform way along the flare ribbon (compare the resulting curves along the two tracking paths N1 and N2 for the northern flare ribbon and along S1 and S2 for the southern flare ribbon, and see also Fig. 1) which has been observed also in earlier studies (see e.g., Temmer et al., 2007). The (velocity) acceleration time profile of the CME, as derived from combined EUV and COR1 measurements (cf. Section 2.4), reveals a close relation with the time evolution of (the derivative of) the GOES X-ray flux. The reconnected flux associated with ...
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... −1 , we estimate the ICME to arrive at Earth on 2011 October 5 at 07:37 UT (± 5 h), with an impact speed of 426 km s −1 (± 30 km s −1 ). Comparison with Wind observations allows us to determine the arrival of the CME-associated shock at 07:36 UT, with an impact speed of ∼460 km s −1 and followed by a magnetic structure lasting from ∼10-22 UT (cf. Fig. 10). The ICME caused a moderate geomagnetic storm of Dst=−43 nT ( Richardson and Cane, 2010, "R&C List" 4 ). The modeled and measured results show a quite good match revealing that the CME only marginally decelerated on its way from Sun to ...
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... see top right panel in Fig. 9). Importantly, this result is in accordance with the direction of propagation derived from GCS modeling, so that we can safely use the value of E15 for the conversion of the measured elongation angle to radial distances, and thus, for deriving the (I)CME kinematics, including the speed and acceleration profiles (see Fig. 10a-c and Section 2.4 for details). The CME front as observed in HI1+2 cannot be entirely tracked to the distance of L1, however, inspecting Fig. 10a, we see that a linear extrapolation of the derived kinematics would match well with the arrival of the CME at Wind ...
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... can safely use the value of E15 for the conversion of the measured elongation angle to radial distances, and thus, for deriving the (I)CME kinematics, including the speed and acceleration profiles (see Fig. 10a-c and Section 2.4 for details). The CME front as observed in HI1+2 cannot be entirely tracked to the distance of L1, however, inspecting Fig. 10a, we see that a linear extrapolation of the derived kinematics would match well with the arrival of the CME at Wind ...
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... plasma and magnetic field properties measured in-situ by Wind, covering the time range 2011 October 4 00:00 UT to October 6 24:00 UT, are shown in Fig. 10d-i. They suggest that the CME shock-sheath structure arrived at Earth on October 5 at 07:36 UT (indicated by the blue dashed vertical line). Signatures typical for a MC (Burlaga, 1991) were observed, including (i) a rotating magnetic field vector (between 10:00 UT and 22:00 UT; see Fig. 10e- g), (ii) an enhanced magnetic field strength ...
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... October 4 00:00 UT to October 6 24:00 UT, are shown in Fig. 10d-i. They suggest that the CME shock-sheath structure arrived at Earth on October 5 at 07:36 UT (indicated by the blue dashed vertical line). Signatures typical for a MC (Burlaga, 1991) were observed, including (i) a rotating magnetic field vector (between 10:00 UT and 22:00 UT; see Fig. 10e- g), (ii) an enhanced magnetic field strength (Fig. 10d), and (iii) a temperature below the typical quiet solar wind temperature ( Richardson and Cane, 1995). Applying a Lundquist model to the in situ measured data, we deduce an axial field strength of B 0 =12.1 nT, a radius of the MC of r 0 =1.75·10 12 cm, and a Figure 9. Left: ...
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... in Fig. 10d-i. They suggest that the CME shock-sheath structure arrived at Earth on October 5 at 07:36 UT (indicated by the blue dashed vertical line). Signatures typical for a MC (Burlaga, 1991) were observed, including (i) a rotating magnetic field vector (between 10:00 UT and 22:00 UT; see Fig. 10e- g), (ii) an enhanced magnetic field strength (Fig. 10d), and (iii) a temperature below the typical quiet solar wind temperature ( Richardson and Cane, 1995). Applying a Lundquist model to the in situ measured data, we deduce an axial field strength of B 0 =12.1 nT, a radius of the MC of r 0 =1.75·10 12 cm, and a Figure 9. Left: Interplanetary propagation of the CME under study (red line) ...
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... temmer_revised2.tex; 15 October 2018; 12:13; p. 17 Table 2. In situ characteristics using a cylindrical force free model fit (see Fig. 10). For comparison we list the parameter values as derived from NLFF model results and the solar source region ...
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... Here, H s denotes the helicity sign, which is set to −1, corresponding to the left-handed flux rope deduced from the in situ observed ICME signature (see Fig. 10d-i) and L is the length of the MC that is calculated from the circum- ference of the GCS model result viewed face-on at 1 AU (see Table 1). As a result, we obtain for the MC Φ ax =5.2·10 20 Mx and H=−1.8·10 42 Mx 2 , in basic agreement within a factor of two with the corresponding values derived for its source region on the Sun (summarized ...
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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.
