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Peer-reviewedCC BY 4.0The Astrophysical Journal

A New Understanding of the Formation Phases of Fast Coronal Mass Ejections and Their Role in Shock Formation and Particle Acceleration

  • Laura A. Balmaceda1,2
  • Angelos Vourlidas3
  • Laura Rodríguez-García4,5
  • Christian Palmroos6
  • Nina Dresing6
6 affiliations
  1. 1NASA Goddard Space Flight Center
  2. 2George Mason University
  3. 3The Johns Hopkins University Applied Physics Laboratory
  4. 4European Space Agency (ESA)
  5. 5Universidad de Alcalá
  6. 6University of Turku
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Abstract

We uncover a new pattern in the formation of fast coronal mass ejections (CMEs), consisting of three phases: a rapid lateral expansion ( hyperinflation ) lasting <10 minutes, followed by a slower but still asymmetric expansion, which lasts up to 50 minutes (both phases comprising the overexpansion ) and ending in the familiar self-similar expansion phase. The result is based on the analysis of 20 CMEs associated with flares and solar energetic particles (SEPs), which were comprehensively observed from multiple viewpoints at high cadence. To understand the role of the early expansion phase of CMEs in the formation of coronal shocks and consequent SEP acceleration, we studied the temporal relationship with other solar phenomena, including X-ray flares and radio emission. We find that (1) all events exhibit the three-stage formation sequence; (2) the overexpansion phase drives the shock and extreme-UV (EUV) wave, and explains why metric type II sources tend to form at CME flanks; (3) the hyperinflation phase is cotemporal to the flare impulsive phase, suggesting a common origin that is likely the addition of poloidal flux in the forming magnetic flux rope (MFR). Finally, we find that near-relativistic ∼53–105 keV) electrons are released first, near the flare peak and the onset of Type II. Note that ∼25 MeV protons are released later, toward the end of CME overexpansion, when shocks have formed. Our results clarify long-standing questions in the field and will contribute toward improved particle radiation forecasting schemes.

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Cite

BibTeXRIS
BibTeX
@article{balmaceda2026understanding,
  title = {{A New Understanding of the Formation Phases of Fast Coronal Mass Ejections and Their Role in Shock Formation and Particle Acceleration}},
  author = {Laura A. Balmaceda and Angelos Vourlidas and Laura Rodríguez-García and Christian Palmroos and Nina Dresing},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea083},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea083},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - A New Understanding of the Formation Phases of Fast Coronal Mass Ejections and Their Role in Shock Formation and Particle Acceleration
AU  - Laura A. Balmaceda
AU  - Angelos Vourlidas
AU  - Laura Rodríguez-García
AU  - Christian Palmroos
AU  - Nina Dresing
PY  - 2026
DA  - 2026/10/09
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea083
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea083
AB  - We uncover a new pattern in the formation of fast coronal mass ejections (CMEs), consisting of three phases: a rapid lateral expansion ( hyperinflation ) lasting <10 minutes, followed by a slower but still asymmetric expansion, which lasts up to 50 minutes (both phases comprising the overexpansion ) and ending in the familiar self-similar expansion phase. The result is based on the analysis of 20 CMEs associated with flares and solar energetic particles (SEPs), which were comprehensively observed from multiple viewpoints at high cadence. To understand the role of the early expansion phase of CMEs in the formation of coronal shocks and consequent SEP acceleration, we studied the temporal relationship with other solar phenomena, including X-ray flares and radio emission. We find that (1) all events exhibit the three-stage formation sequence; (2) the overexpansion phase drives the shock and extreme-UV (EUV) wave, and explains why metric type II sources tend to form at CME flanks; (3) the hyperinflation phase is cotemporal to the flare impulsive phase, suggesting a common origin that is likely the addition of poloidal flux in the forming magnetic flux rope (MFR). Finally, we find that near-relativistic ∼53–105 keV) electrons are released first, near the flare peak and the onset of Type II. Note that ∼25 MeV protons are released later, toward the end of CME overexpansion, when shocks have formed. Our results clarify long-standing questions in the field and will contribute toward improved particle radiation forecasting schemes.
SN  - 0004-637X
SN  - 1538-4357
ER  -