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The Dual Nature of Solar Wind Structuring: Resonant Standing Waves and Laval Nozzle Dynamics in Coronal Streamers

Olena Podladchikova

TL;DR

This paper resolves the puzzle of periodic density structures in the solar wind by proposing a dual-mechanism framework for coronal streamers. It combines a magnetohydrodynamic resonator model, where standing slow waves establish global PDS with discrete periods $P_n^{\text{res}} = \frac{2L}{n c_s}$, and a Laval nozzle model, where overexpanded geometry drives local oscillations with periods $P_n^{\text{nozzle}} = \frac{L_{\text{over}}}{v_{\text{SW}}} \cdot k_n$. The work shows that resonant dynamics dominate PDS formation across ~85% of streamers, while nozzle oscillations operate in ~35% to generate shock diamonds and vortices, producing a coherent, hierarchical view of solar wind structuring with implications for astrophysical plasma flows. Overall, the dual-mechanism framework resolves longstanding questions about PDS coherence, persistence to 1 AU with minimal energy loss, and the interplay between global and local flow processes in coronal streamers.

Abstract

Periodic Density Structures (PDS) observed in white-light coronagraphs represent a fundamental challenge to conventional solar wind paradigms. Through systematic analysis of multi-instrument observations and theoretical modeling, we demonstrate that coronal streamers operate as dual-nature systems: magnetohydrodynamic resonators that establish global periodicity through standing waves (122, 61, 41 minutes) and Laval nozzles that generate local flow structures through shock-driven oscillations (93, 47, 31, 23 minutes). The resonant mechanism dominates PDS formation, explaining their universal occurrence across 85\% of streamers, coherence over 10+ cycles, and persistence to 1 AU with only 0.1\% energy loss. Nozzle oscillations, while limited to 35\% of overexpanded streamers and maintaining only 1-2 cycle coherence, play crucial secondary roles in vortex formation and provide the essential converging-diverging geometry for supersonic solar wind acceleration. This dual-mechanism framework resolves longstanding puzzles in solar wind structuring while revealing the hierarchical organization of standing-wave and flow processes in astrophysical plasmas.

The Dual Nature of Solar Wind Structuring: Resonant Standing Waves and Laval Nozzle Dynamics in Coronal Streamers

TL;DR

This paper resolves the puzzle of periodic density structures in the solar wind by proposing a dual-mechanism framework for coronal streamers. It combines a magnetohydrodynamic resonator model, where standing slow waves establish global PDS with discrete periods , and a Laval nozzle model, where overexpanded geometry drives local oscillations with periods . The work shows that resonant dynamics dominate PDS formation across ~85% of streamers, while nozzle oscillations operate in ~35% to generate shock diamonds and vortices, producing a coherent, hierarchical view of solar wind structuring with implications for astrophysical plasma flows. Overall, the dual-mechanism framework resolves longstanding questions about PDS coherence, persistence to 1 AU with minimal energy loss, and the interplay between global and local flow processes in coronal streamers.

Abstract

Periodic Density Structures (PDS) observed in white-light coronagraphs represent a fundamental challenge to conventional solar wind paradigms. Through systematic analysis of multi-instrument observations and theoretical modeling, we demonstrate that coronal streamers operate as dual-nature systems: magnetohydrodynamic resonators that establish global periodicity through standing waves (122, 61, 41 minutes) and Laval nozzles that generate local flow structures through shock-driven oscillations (93, 47, 31, 23 minutes). The resonant mechanism dominates PDS formation, explaining their universal occurrence across 85\% of streamers, coherence over 10+ cycles, and persistence to 1 AU with only 0.1\% energy loss. Nozzle oscillations, while limited to 35\% of overexpanded streamers and maintaining only 1-2 cycle coherence, play crucial secondary roles in vortex formation and provide the essential converging-diverging geometry for supersonic solar wind acceleration. This dual-mechanism framework resolves longstanding puzzles in solar wind structuring while revealing the hierarchical organization of standing-wave and flow processes in astrophysical plasmas.

Paper Structure

This paper contains 10 sections, 5 equations, 3 figures.

Table of Contents

  1. Introduction: The Puzzle of Periodic Structures
  2. The Streamer as a Magnetohydrodynamic Resonator
  3. The Streamer as an Oscillating Laval Nozzle
  4. Natural Formation of Laval Nozzle Geometry
  5. Magnetic Field Structure
  6. Gravitational Influence
  7. Force Balance and Throat Location
  8. Oscillation Mechanism in Overexpanded Regime
  9. Nozzle Oscillation Periods
  10. Observational Signatures and Timing

Figures (3)

  • Figure 1: Streamer resonator mechanism. Standing magnetoacoustic waves create periodic density structures (PDS) at anti-nodes. Three harmonic modes produce observed periods of 122, 61, and 41 minutes.
  • Figure 2: Non-oscillating regimes of coronal streamers as Laval nozzles. (a) Underexpanded regime: Prandtl-Meyer expansion fans (10-20% contrast). (b) Optimally expanded regime: smooth flow. Neither regime supports oscillations.
  • Figure 3: Oscillating regime in coronal streamers: Overexpanded ($P_{\text{exit}} < P_{\infty}$) - the only regime supporting oscillations. Features shock diamonds (standing wave patterns creating 20-40% density enhancements) and vortex formation (quasi-periodic density blobs with 10-20% enhancement from Kelvin-Helmholtz instabilities) due to flow separation. Only $\sim$35% of streamers operate in this regime (Viall2015).