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Statistical properties of spicules in MURaM-ChE

Sanghita Chandra, Robert Cameron, Damien Przybylski, Sami K. Solanki

TL;DR

This work investigates spicules in a 3D radiative-MHD simulation with chromospheric extension (MURaM-ChE) by identifying off-limb spicule-like features with an Hα proxy and comparing their statistics to Hinode/SOT Ca II H observations. The authors demonstrate self-consistent formation of both type I and type II spicules in the enhanced-network model without ambipolar diffusion, and they quantify lifetimes, speeds, lengths, widths, inclinations, and heights, finding broad agreement with observations for several properties. The study also links spicules to on-disc RBEs and RREs, revealing multi-threaded, bi-directional or cyclical mass flows consistent with complex chromospheric dynamics. Overall, the results validate the modeling approach, provide 3D context for spicule velocities and morphologies, and offer insights into the connection between limb spicules and disc counterparts, with implications for chromospheric heating and mass transport.

Abstract

Numerical simulations of the solar chromosphere have progressed towards reproducing spicules, which are transient features observed at the solar limb using spectral lines such as H$α$, Ca II H&K, or Mg II h&k. Two types of spicules, referred to as types I and II, have been identified in observations and studied in previous numerical works. The statistics of type II spicules in 3D numerical simulations have not yet been studied. We aim to compare the statistics of properties such as lengths, lifetimes, widths, heights, inclinations, and maximum velocities of self-consistently formed spicules in a MURaM-ChE simulation with observations. We employ a H$α$ proxy to identify fine-scale structures at the solar limb resembling spicules in a simulation of an enhanced network region. We track the evolution of 58 such features found in a 21-minute time sequence, and compare their dynamical and morphological properties with those derived from quiet-Sun observations using the Solar Optical Telescope (SOT) onboard the Hinode mission in the Ca II H spectral line. Previous studies have shown that spicules show very similar properties in Ca II H and H$α$. The spicule-like structures found in the simulation have statistical properties which are broadly consistent with those observed with Hinode/SOT. In particular, we find evidence for the self-consistent formation of both type I and type II spicules within the simulation, even in the absence of ambipolar diffusion. We also investigate the properties of rapid blueshifted and redshifted excursions (RBEs and RREs) in the simulation in relation to the spicules.

Statistical properties of spicules in MURaM-ChE

TL;DR

This work investigates spicules in a 3D radiative-MHD simulation with chromospheric extension (MURaM-ChE) by identifying off-limb spicule-like features with an Hα proxy and comparing their statistics to Hinode/SOT Ca II H observations. The authors demonstrate self-consistent formation of both type I and type II spicules in the enhanced-network model without ambipolar diffusion, and they quantify lifetimes, speeds, lengths, widths, inclinations, and heights, finding broad agreement with observations for several properties. The study also links spicules to on-disc RBEs and RREs, revealing multi-threaded, bi-directional or cyclical mass flows consistent with complex chromospheric dynamics. Overall, the results validate the modeling approach, provide 3D context for spicule velocities and morphologies, and offer insights into the connection between limb spicules and disc counterparts, with implications for chromospheric heating and mass transport.

Abstract

Numerical simulations of the solar chromosphere have progressed towards reproducing spicules, which are transient features observed at the solar limb using spectral lines such as H, Ca II H&K, or Mg II h&k. Two types of spicules, referred to as types I and II, have been identified in observations and studied in previous numerical works. The statistics of type II spicules in 3D numerical simulations have not yet been studied. We aim to compare the statistics of properties such as lengths, lifetimes, widths, heights, inclinations, and maximum velocities of self-consistently formed spicules in a MURaM-ChE simulation with observations. We employ a H proxy to identify fine-scale structures at the solar limb resembling spicules in a simulation of an enhanced network region. We track the evolution of 58 such features found in a 21-minute time sequence, and compare their dynamical and morphological properties with those derived from quiet-Sun observations using the Solar Optical Telescope (SOT) onboard the Hinode mission in the Ca II H spectral line. Previous studies have shown that spicules show very similar properties in Ca II H and H. The spicule-like structures found in the simulation have statistical properties which are broadly consistent with those observed with Hinode/SOT. In particular, we find evidence for the self-consistent formation of both type I and type II spicules within the simulation, even in the absence of ambipolar diffusion. We also investigate the properties of rapid blueshifted and redshifted excursions (RBEs and RREs) in the simulation in relation to the spicules.

Paper Structure

This paper contains 10 sections, 4 equations, 9 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Model Atmosphere: Enhanced network model
  3. Spicules in the H$\alpha$ proxy
  4. Prescription of the proxy
  5. Synthetic observations degraded to the resolution of Hinode/SOT
  6. Statistical properties of spicules
  7. Relationship of the properties of spicules with RBEs/RREs in MURaM-EN
  8. Discussion
  9. Conclusion
  10. Spicules seen in the time-distance plots

Figures (9)

  • Figure 1: Spicules at the limb in the MURaM-ChE simulations, identified using the H$\alpha$ proxy from the two horizontal directions x and y respectively. The Doppler velocity ($\mathsf{v}_\mathrm{D}$) is at +37 km/s. The photosphere is marked by 0 on the z axis. A movie showing the evolution of these spicules can be found https://owncloud.gwdg.de/index.php/s/hhLnkNkrlfxoVNW.
  • Figure 2: Comparison with Hinode/SOT-like observation. The simulated features at a Doppler shift of -37 km/s identified with the proxy (left) is degraded with the point spread function of an ideal, spiderless 50 cm telescope (right).
  • Figure 3: Evolution of a feature (after degradation to the resolution of Hinode/SOT) resembling a type-II spicule with a maximum apparent velocity of 66 km/s. The panels starting on the left show the evolution of our feature of interest. The orange arrows point to this feature. The time-distance plot for this feature is shown on the right. The slit for the time-distance plot is placed along the axis of the feature during its evolution. The time t = 0 s marks the first prominent appearance of the feature.
  • Figure 4: Spicules, RBEs and RREs seen at different $\mathsf{V}_\mathrm{{los}}$. Panels (a), (b): H$\alpha$ features viewed at the limb at Doppler velocities of +30 km/s (blue) and -30 km/s (red) in panel (a) and $\pm$40 km/s in panel (b). Panels (c), (d): H$\alpha$ features on the disc at the same velocities as in panels (a), (b). The lighter shades of the colour (red/blue) indicate features with higher opacity. The evolution of the features for the entire time-series can be found https://owncloud.gwdg.de/index.php/s/ugf1BIH2RB8613R.
  • Figure 5: Tracking features at a Doppler velocity of +50 km/s (in the same colour scale as Fig. \ref{['telescope']})
  • ...and 4 more figures