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Exploring the Substructures of Coronal Mass Ejections (CMEs) and Their Space Weather Impacts
An approach to identify the compressed region of the magnetic cloud (MC) and marking the MC axis
A pictorial representation that describes the three scenarios to identify the compressed region of the MC based on the arrival of the size and axis center (I) No compression, (ii) Compression at the rear portion, and (iii) Compression at the front portion.
Axis_center_mov.movAn animated cartoon which shows the identification of MC axis for N to S rotated MC.
The right panel plot shows that the MC is compressed at the rear portion of both spacecraft; however, compression is more pronounced at STEREO-A. This implies inhomogeneity in the MC even at mesoscales.
The left and right y-axis of the top and bottom panel shows the in situ measured speed and latitude of the MC. The blue, magenta, and green mark the arrival of the size, time, and axis center.
Disparities in MC characteristics even at mesoscales
The left panel figure depicts the total magnetic field and its components at STEREO-A and Wind in blue and red, respectively. The right panel depicts the differences in the magnetic field parameters at both spacecraft in the black solid line, while the black dashed line represents the zero reference to visualize the difference in the magnetic field parameters. The bottom panel shows the cosine similarity (angle between two vectors) between the magnetic field vectors measured at both spacecraft. We note a disparity in the magnetic field parameters at its rear portion even at its mesoscales.
The top and bottom panels represent the hodogram representation at STEREO-A and Wind, respectively. From the plot, we note that at Wind the MC is slightly out of ecliptic plane while for STEREO-A, the MC is in the ecliptic plane.
Non-conventional approach for deriving the radial sizes and instantaneous expansion speeds of CMEs at different instances
Illustration of non-conventional approach for deriving the radial sizes and instantaneous expansion speeds at different instances. For more details, Agarwal and Mishra 2024.
The figure demonstrates the expansion of a CME during its passage over in situ spacecraft. The magenta-colored circle represents the geometry of the CME in the plane of the spacecraft. The blue, green, and maroon vertical line denotes the leading edge (LE), size center, and trailing edge (TE) of the CME, respectively. The top-to-bottom panels represent the arrival of LE (L), center (C), and TE (T) at 1 AU. The location of in situ spacecraft at 1 AU is marked on the horizontal black line with two additional distances: one less than 1 AU and one greater than 1 AU. The subscripts 1, 2, and 3 represent the traits of the CME at the arrival of LE, center, and TE, respectively. The left-right arrow represents the distance traveled by different substructures during any two instances. Our non-conventional approach utilizes the equation of motion to determine the evolution of radial size and instantaneous expansion speed of the CME.
The figure depicts the in situ speed profile of the 2010 April 3 CME. The arrival of CME substructures such as shock, LE, size center, and TE are shown in the red, blue, green, and maroon vertical lines. This figure demonstrates the difference between the time center (in black) and the size center for the CME. Moreover, a greater disparity between both the center is shown by utilizing a highly expanding virtual CME speed profile in yellow.
The left and right y-axis of the right panel shows the in situ measured speed and acceleration of the CME. The blue, green, and maroon represent the thickness of the CME substructures LE, center, and TE for deriving their acceleration when multi-point in situ measurements are not available.
Our non-conventional approach utilizes the constant acceleration of CME substructures to estimate the radial sizes and instantaneous expansion speed of CMEs in different instances. The propagation speed of CME substructures at an instance when their speed is not measured at 1 AU (at in situ spacecraft) is estimated by utilizing the first equation of motion and constant acceleration of the corresponding substructure. The propagation speeds of CME substructures at the same instance are utilized to estimate the instantaneous expansion speed. Since the single point in-situ measurements are unable to provide the constant acceleration of CME substructures. Therefore, we use a certain thickness of the CME substructures to estimate the acceleration from a single point in-situ speed profile. Additionally, the second equation of motion is utilized to estimate the distance traveled by CME substructures during any two instances and the evolution of the radial size of the CME during its passage over the in situ spacecraft.
Evolution of 2010 April 3 CME in the coronagraphs and heliospheric imagers of STEREO-A and STEREO-B.
The figure depicts the evolution of CME substructures, such as leading edge and size center, and radius in the interplanetary medium. The top-to-bottom panels represent the 3D height, speed, and acceleration of the CME substructures and CME radius up to the arrival of CME LE at 1 AU.
The evolution of radial size and expansion speed dependency on the measure of radial dimension with respect to CME increasing distance from the Sun.
The upper and lower panels show the evolution of the radial size and expansion speed of the MC with the height of its LE for three different values of k. The green, orange, and blue denote the k values as 0.25, 0.35, and 0.45, respectively. The black-filled triangle denotes the in situ measured radial size and expansion speed at 1 AU from the conventional analysis approach to in situ observations of the CME. The error bar over each data point is shown with transparent fill areas of the same color as the corresponding data point.
A non-constant profile for the aspect ratio - measure of radial dimension with respect to CME increasing distance.
The top-to-bottom panels show the time evolution of the CME LE height, aspect ratio, radial size, and expansion speed. The red dotted and blue dashed lines denote the evolution of k in the IP medium, with two power laws decreasing the value of k for heights beyond 30 and 70 solar radii, respectively.
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