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The Missing Mechanism: Picoflare Heating in the Solar Corona

Olena Podladchikova

TL;DR

The paper addresses the missing mechanism in coronal heating by leveraging Solar Orbiter observations that reveal picoflares spanning $3×10^{20}$–$10^{24}$ erg, below the traditional nanoflare floor. It develops a dual-mechanism framework: looptop tearing-mode reconnection (Population A) and footpoint anomalous resistivity (Population B), with energy transfer mediated by reconnection-generated electric fields and chromospheric transport mechanisms. Key contributions include a bimodal energy distribution with slopes $α ≈ 2.32$ and $α ≈ 2.82$, a clear spatial separation (looptops at 2.5–5 Mm vs footpoints at 1–2.5 Mm), and a coherent energy budget that converges at the low-energy end, implying that numerous small picoflares dominate coronal heating. This framework resolves the long-standing EUV nanoflare location debate, bridges photospheric energy injection to coronal thermalization, and provides a concrete path for future Solar Orbiter campaigns to refine the energy-partition picture.

Abstract

The coronal heating problem has been explored through wave heating and impulsive nanoflare paradigms. Solar Orbiter observations reveal picoflares (10^20-10^24 erg) extending below the Parker-Aschwanden minimal coronal nanoflare limit. These events involve two distinct mechanisms: short-duration looptop tearing-mode reconnection and long-duration footpoint anomalous resistivity. This dual-mechanism framework resolves the long-standing energy partition paradox and bridges photospheric energy injection with coronal thermalization.

The Missing Mechanism: Picoflare Heating in the Solar Corona

TL;DR

The paper addresses the missing mechanism in coronal heating by leveraging Solar Orbiter observations that reveal picoflares spanning – erg, below the traditional nanoflare floor. It develops a dual-mechanism framework: looptop tearing-mode reconnection (Population A) and footpoint anomalous resistivity (Population B), with energy transfer mediated by reconnection-generated electric fields and chromospheric transport mechanisms. Key contributions include a bimodal energy distribution with slopes and , a clear spatial separation (looptops at 2.5–5 Mm vs footpoints at 1–2.5 Mm), and a coherent energy budget that converges at the low-energy end, implying that numerous small picoflares dominate coronal heating. This framework resolves the long-standing EUV nanoflare location debate, bridges photospheric energy injection to coronal thermalization, and provides a concrete path for future Solar Orbiter campaigns to refine the energy-partition picture.

Abstract

The coronal heating problem has been explored through wave heating and impulsive nanoflare paradigms. Solar Orbiter observations reveal picoflares (10^20-10^24 erg) extending below the Parker-Aschwanden minimal coronal nanoflare limit. These events involve two distinct mechanisms: short-duration looptop tearing-mode reconnection and long-duration footpoint anomalous resistivity. This dual-mechanism framework resolves the long-standing energy partition paradox and bridges photospheric energy injection with coronal thermalization.
Paper Structure (12 sections, 8 equations, 3 figures, 1 table)

This paper contains 12 sections, 8 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observational Basis: Two Populations of Picoflares
  3. Population A: Looptop Events
  4. Population B: Footpoint Events
  5. Theoretical Framework: From Parker's Nanoflares to Picoflares
  6. Parker's Nanoflare Model and Its Limitations
  7. Aschwanden's Scaling and the Coronal Nanoflare Limit
  8. The Priest School: Tearing-Mode Instability and Current Sheet Formation
  9. Anomalous Resistivity: The Missing Mechanism for Low-Energy Picoflares
  10. Reconnection-Generated Electric Fields and Footpoint Heating
  11. Chromospheric Electric Field Transport Mechanisms
  12. Conclusion

Figures (3)

  • Figure 1: The quiet-Sun corona as seen by Solar Orbiter/EUI, revealing the resolved structure of "campfires" Berghmans2021. These impulsive brightenings are fundamental drivers of coronal heating. See the supplementary https://drive.google.com/file/d/1Kmn8mrvktAV210Adx7phBkb5TNJ98TMY/view?usp=sharing.
  • Figure 2: Picoflare events resolved by Solar Orbiter/EUI from 0.5 AU, confirming what was inferred statistically Benz1998Aschwanden2000. (Left) Population A: looptop brightening from tearing-mode reconnection ($3.2 \times 10^{23}$ erg) https://drive.google.com/file/d/1f9sU5JUjBubawXHbnpR3pCITFFmruOr7/view?usp=sharing. (Middle) Population B: footpoint heating from anomalous resistivity ($1.7 \times 10^{22}$ erg) https://drive.google.com/file/d/1NAMaxNvxBawTGt8mCNMUY8RkARi2y7a-/view?usp=sharing. (Right) Coupled A-B Event: Looptop reconnection driving footpoint dissipation https://drive.google.com/file/d/1NAMaxNvxBawTGt8mCNMUY8RkARi2y7a-/view?usp=sharing.
  • Figure 3: Schematic of atmospheric energy transfer: photospheric twisting (1-2) leads to loop-top reconnection (3, Population A) and footpoint heating (4-5, Population B), with characteristic timescales.