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Early Evolution of Earth-Directed Coronal Mass Ejections in the Vicinity of Coronal Holes

This study analyzes 49 Earth-directed coronal mass ejections from 2010 to 2020 to demonstrate that coronal holes significantly influence their deflection and rotation in the low corona via magnetic forces, though this effect diminishes with distance and is inversely correlated with CME velocity.

Original authors: Suresh Karuppiah, Mateja Dumbović, Karmen Martinić, Manuela Temmer, Stephan G. Heinemann, Bojan Vršnak

Published 2026-04-30

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CC BY 4.0

Original authors: Suresh Karuppiah, Mateja Dumbović, Karmen Martinić, Manuela Temmer, Stephan G. Heinemann, Bojan Vršnak

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Sun as a giant, fiery factory that constantly shoots out massive bubbles of superheated gas and magnetic fields. These bubbles are called Coronal Mass Ejections (CMEs). Sometimes, these bubbles head straight for Earth, and if they hit us, they can cause "space weather" like auroras or even disrupt our power grids and satellites.

Scientists have long wondered: Do these bubbles travel in a straight line, or do they get pushed around on their way to Earth?

This paper investigates whether Coronal Holes (CHs)—which are like giant, open "windows" in the Sun's magnetic atmosphere where gas escapes very fast—act like invisible walls or magnets that push these bubbles off course.

Here is the story of their findings, explained simply:

1. The Setup: Tracking 49 Space Bubbles

The researchers acted like cosmic detectives. They looked back at 49 specific events between 2010 and 2020 where these solar bubbles were heading toward Earth.

To see exactly where these bubbles were going, they used a special 3D modeling tool (called the GCS model) that works like a digital wireframe. Imagine trying to guess the shape of a moving cloud by looking at it from two different windows (spacecraft) at the same time. By combining these views, they could build a 3D model of the bubble and track its path step-by-step as it flew away from the Sun.

2. The Suspects: Coronal Holes

On the Sun, there are dark, cooler patches called Coronal Holes. Think of these as "open doors" in the Sun's magnetic fence. Because the fence is open there, the solar wind (the Sun's constant breeze) rushes out much faster than elsewhere.

The scientists wanted to know: If a solar bubble flies near one of these "open doors," does the magnetic force from the hole push the bubble sideways or spin it around?

To measure this "push," they invented a score called CHIP (Coronal Hole Influence Parameter).

The Analogy: Imagine the Coronal Hole is a giant magnet. The CHIP score is a calculation of how strong that magnet is (based on its size and magnetic power) and how close the solar bubble is to it. The closer and stronger the magnet, the higher the CHIP score.

3. The Investigation: What Happened?

The team tracked the bubbles from the moment they left the Sun's surface (the "low corona") all the way out into space. They looked for two things:

Deflection: Did the bubble change its direction (like a car swerving)?
Rotation: Did the bubble spin around its own axis (like a rolling pin)?

The Key Findings:

The "Low Corona" is the Critical Zone: The study found that the "push" from the Coronal Holes (the CHIP score) only really matters when the bubble is very close to the Sun (within about 10 times the Sun's radius).
- Analogy: Think of a sailboat leaving a harbor. The wind from the shore (the Coronal Hole) can push the boat hard while it's still near the dock. But once the boat is out in the open ocean, that specific wind from the shore doesn't matter anymore; the boat just sails on its own momentum.
- Result: The researchers found a strong statistical link between a high CHIP score (a strong nearby magnetic push) and the bubble changing direction early in its journey. Once the bubble got far away, the Coronal Holes stopped having a noticeable effect.
Speed Matters: They discovered a funny relationship with speed. Faster bubbles were harder to push.
- Analogy: Imagine trying to push a shopping cart. If the cart is empty and moving slowly, it's easy to knock it off course. But if the cart is zooming by at full speed, it's very hard to make it swerve.
- Result: The faster the solar bubble was traveling, the less it got deflected by the Coronal Holes.
Spinning vs. Swerving: While the bubbles did change direction (swerve), the "push" from the holes didn't seem to be the main reason they started spinning. The spinning seemed to be caused by other things happening right at the moment the bubble erupted from the Sun.

4. The Conclusion

The paper concludes that Coronal Holes are like traffic cops in the early stages of a solar storm. They can definitely tell a solar bubble to "swerve" left or right if the bubble is slow and the hole is strong and close by.

However, this influence is short-lived. Once the bubble gets far enough away from the Sun, the Coronal Holes lose their grip, and the bubble continues on its path, largely unaffected by those specific magnetic holes.

In short: If you want to predict if a solar storm will hit Earth, you need to check if there are any "open windows" (Coronal Holes) nearby at the very moment the storm leaves the Sun. If the storm is fast, it might ignore them anyway. But if it's slow and the hole is close, the storm might get pushed off course, potentially missing Earth or hitting us harder than expected.

1. Problem Statement

Coronal Mass Ejections (CMEs) are primary drivers of severe space weather and geomagnetic storms. A critical challenge in space weather forecasting is predicting the trajectory of Earth-directed CMEs, as their geoeffectiveness depends heavily on their arrival direction and magnetic configuration. Previous studies indicate that CMEs often undergo non-radial propagation, exhibiting deflection (change in latitude/longitude) and rotation (change in tilt) due to background magnetic fields and solar wind structures.

While the influence of Coronal Holes (CHs)—regions of open magnetic field lines and high-speed solar wind—on CME trajectories is known, the specific mechanisms, the altitude at which these interactions occur, and the quantitative relationship between CH properties and CME kinematics remain under-explored. This study aims to systematically analyze the deflection and rotation of Earth-directed CMEs in the vicinity of CHs to determine if CHs act as significant deflectors and to identify the coronal height range where this influence is most dominant.

2. Methodology

The study employs a statistical analysis of 49 Earth-directed CMEs occurring between 2010 and 2020. The methodology integrates multi-viewpoint observations with 3D modeling and magnetic parameterization:

Data Selection:
- CMEs: Selected from the Richardson and Cane (2010) ICME catalog. Events were filtered based on data availability from SDO/AIA (for low coronal signatures), SOHO/LASCO, and STEREO/SECCHI (for stereoscopic coronagraphic data).
- Exclusion Criteria: Events were removed if they lacked sufficient vantage points for 3D reconstruction, had faint signatures, occurred before SDO operations, or involved CME-CME interactions that obscured individual evolution.
3D Reconstruction (GCS Model):
- The Graduated Cylindrical Shell (GCS) model was applied to white-light coronagraph images from multiple viewpoints (SOHO and STEREO-A/B).
- Reconstructions were performed at multiple time steps from the CME's entry into the COR1 field of view (FOV) to its exit from COR2.
- Deflection/Rotation Metrics: Changes in longitude, latitude, and tilt (inclination) were calculated by comparing the first and last GCS reconstructions. Significant changes were defined as those exceeding observational uncertainties (e.g., >11° for longitude, >6° for latitude, >25° for tilt).
Coronal Hole Characterization:
- CHs were identified using SDO/AIA 193 Å images and automated tools (CHIMERA, SPOCA, CATCH).
- Coronal Hole Influence Parameter (CHIP): A force-like parameter was calculated for each event to quantify the CH's influence. The formula is:
  $CHIP = \frac{B \cdot A}{d^2}$
  Where $B$ is the line-of-sight magnetic field strength, $A$ is the CH area, and $d$ is the distance between the CME source and the CH center of mass.
- Temporal Stages: CHIP was calculated at three distinct stages to represent different coronal heights:
  - CHIP1: Distance at the eruption onset (Low Corona).
  - CHIP2: Distance when the CME enters the COR1 FOV (Middle Corona).
  - CHIP3: Distance when the CME reaches the COR2 FOV (High Corona).
Statistical Analysis:
- The study utilized Student's t-tests and the Kolmogorov-Smirnov test to compare distributions of deflection/rotation between events with high and low CHIP values.
- Bootstrapping was used to assess correlations between deflection rates and CME velocities.

3. Key Contributions

Systematic 3D Analysis: Unlike previous studies relying on 2D projections, this work utilizes full 3D GCS reconstructions to accurately determine the true propagation direction and rotation of CMEs.
Height-Dependent Influence: The study introduces a novel approach by calculating CHIP at three distinct evolutionary stages (CHIP1, CHIP2, CHIP3), allowing for the isolation of CH influence in the low, middle, and high corona.
Quantitative Correlation: It provides statistical evidence linking the magnetic properties of CHs (via CHIP) specifically to the overall change in CME direction, rather than just individual components (latitude vs. longitude).

4. Key Results

Deflection and Rotation Statistics:
- Out of 49 events, 1 showed significant longitudinal deflection, 10 showed latitudinal deflection, and 11 showed significant rotation.
- Most latitudinal deflections (8 out of 10) were toward the North.
- Regarding CH interaction, 7 events deflected away from nearby CHs, while 3 deflected toward them.
CHIP and Directional Change:
- Low Corona Dominance: A statistically significant difference ( $p=0.0006$ ) was found between events with and without directional changes specifically for CHIP1 (low corona). No significant correlation was found for CHIP2 or CHIP3.
- Trajectory Evolution: The mean values of CHIP suggest a pattern where CMEs initially move toward the CH (CHIP2 > CHIP1) and subsequently deflect away (CHIP3 < CHIP2).
Deflection/Rotation Rates vs. Height:
- Deflection Rate: High below $10 R_\odot$ (solar radii) and decays significantly beyond this height.
- Rotation Rate: Remains effective up to approximately $15 R_\odot$ before decaying.
Velocity Correlation:
- A significant negative correlation ( $r \approx -0.60$ ) was observed between CME 3D velocity and deflection rate. Faster CMEs experience less deflection, suggesting that high inertia allows them to overcome the magnetic pressure of the CH more effectively.
- No significant correlation was found between rotation rate and velocity.

5. Significance

This research confirms that Coronal Holes play a critical role in the early evolution of Earth-directed CMEs, specifically within the low corona (below ~10 $R_\odot$ ). The findings suggest that:

Magnetic Forces are Primary: The deflection and rotation of CMEs are predominantly driven by magnetic gradients associated with CHs in the low corona, rather than interplanetary forces.
Predictive Value: The CHIP parameter, particularly in the low corona, serves as a viable indicator for predicting whether a CME will undergo a significant change in trajectory.
Velocity Dependence: The speed of a CME is a crucial factor in its susceptibility to deflection; faster CMEs are less likely to be deflected by CHs.

These insights refine space weather models by highlighting the necessity of accounting for low-coronal magnetic structures (specifically CHs) and CME kinematics when forecasting the arrival direction and potential impact of CMEs on Earth.