Solar Physics

, Volume 88, Issue 1–2, pp 163–177 | Cite as

The stability of coronal loops: Finite-length and pressure-profile limits

  • G. Einaudi
  • G. Van Hoven


Results are described from a quickly converging, necessary-and-sufficient, MHD-stability test for coronal-loop models. The primary stabilizing influence arises from magnetic line tying at the photosphere, and this end conditions requires a series expansion of possible loop excitations. The stability boundary is shown to quickly approach a limit as the number of terms increases, providing a critical length for the loop in proportion to its transverse magnetic scale. Several models of force-free-field profiles are tested and the stability behavior of a localized current channel, embedded in an external current-free region, is shown to be superior to that of other, broader, current profiles. Pressure-gradient effects, leading to increased or decreased stability, are shown to be amplified by line tying. Long loops must either conduct low net current, or exhibit an axial-field reversal coexisting with a low-pressure core. The limits on stability depend on the magnetic aspect ratio, the plasma-to-magnetic pressure ratio, and the field orientation at the loop edge. Applications of these results to the structure of coronal loops are described.


Pressure Ratio Stability Boundary Current Channel Coronal Loop Critical Length 
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Copyright information

© D. Reidel Publishing Company 1983

Authors and Affiliations

  • G. Einaudi
    • 1
    • 2
  • G. Van Hoven
    • 3
  1. 1.Scuola Normale SuperiorePisaItaly
  2. 2.University of CaliforniaIrvineUSA
  3. 3.University of CaliforniaIrvineUSA

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