Propagation and Energy Dissipation of Shock Waves in the Solar Chromosphere

TL;DR

This work investigates how chromospheric shocks, excited by subsurface convection, propagate through the lower solar atmosphere using coordinated SST, IRIS, and SDO observations. It shows that shocks form in the chromosphere and persist as they ascend, leaving signatures in both chromospheric lines and transition-region channels, with some evidence of coronal signatures. By combining multi-height spectroscopy with STiC inversions, the authors estimate the shock energy flux and compare it to chromospheric radiative losses, finding that shocks can contribute significantly to energy deposition though not sole heating. The findings highlight the role of magnetic-field topology in wave propagation and energy transport, and they point to the need for high-resolution future observations to fully understand chromospheric heating processes.

Abstract

The solar atmosphere is permeated by various types of waves that originate from subsurface convection. As these waves propagate upward, they encounter they encounter a steep decrease in the density of the medium, leading to their steepening into shock waves. These shock waves typically exhibit a characteristic sawtooth pattern in wavelength-time ($λ$-t) plots of various chromospheric spectral lines, viz., H$α$, Ca II 8542 Å to name a few. In this study, we investigate the propagation of shock waves in the lower solar atmosphere using coordinated observations from the Swedish 1-meter Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO). Our analysis reveals that after forming in the chromosphere, these shock waves travel upward through the solar atmosphere, with their signatures detectable not only in the transition region but also in low coronal passbands. These shock waves dissipate their energy into the chromosphere as they propagate. In certain cases, the energy deposited by these waves is comparable to the radiative losses of the chromosphere, highlighting their potential role in chromospheric heating. Our findings reported here provide crucial insights into wave dynamics in the lower solar atmosphere and their contribution to the energy transport process in the chromosphere.

Figures (11)

• Figure 1: Panels (a) and (b) represent the blue wing and line center filtergrams of H$\alpha$, while panels (c) and (d) correspond to the blue wing and line center filtergrams of Ca II IR. Panels (e) and (f) illustrate the near-simultaneous appearance of the coordinated transition region and corona.
• Figure 2: The right panel displays six columns of $\lambda$-t plots, each corresponding to a different location marked by colored X symbols in the left panel. Each column represents coordinated chromospheric observations, with the top row showing the Stokes I parameter of H$\alpha$, followed by the Stokes I and Stokes V parameters of the Ca II 8542 Å spectral line. The left panel consists of two columns: the first shows the average chromospheric appearance in the blue wing of H$\alpha$ (H$\alpha$ - 0.8 Å), the average HMI magnetogram, and the coronal structure from the SDO/AIA 171 Å channel, while the second provides a zoomed-in view (cyan box) highlighting shock wave locations. The LOS magnetic field strength at each studied point is indicated atop the respective $\lambda$-t plot. Notably, when the photospheric field exceeds 100 G, shock waves are detected in both Stokes I and Stokes V parameters, whereas weaker fields (<30 G) lack a clear Stokes V signature, as seen in location (e) which was expected.
• Figure 3: Panel (a) shows the average appearance of the chromosphere in the blue wing of Ca II 8542 Å (Ca II 8542 Å - 0.8 Å), with 50 selected shock wave locations marked by colored X symbols. Panels (b) and (c) show histograms of the average magnetic field strength and inclination in the photosphere, comparing the distributions at the identified shock wave locations with those across the entire FoV. These 50 shock waves are shown in Figure \ref{['FigA1']}.
• Figure 4: Five rows of $\lambda$-t plots for five selected locations ((g)--(k)), showing different atmospheric layers from left to right: the middle chromosphere (Ca II 8542 Å), upper chromosphere (Mg II K 2796 Å), and transition region (C II 1336 Å, Si IV 1394 Å, and Si IV 1403 Å). The detection of shock wave signatures in transition region lines indicates their upward propagation through the solar atmosphere.
• Figure 5: Light curves from the mid chromosphere (H$\alpha$ and Ca II 8542 Å line centers), upper chromosphere (Mg II K 2796 Å) and the transition region (Si IV 1400 Å) for three selected locations. These locations, marked by X and labeled as (a), (b), and (e) in the left panel of Figure \ref{['Fig2']}, correspond to locations [0], [1], and [4] in panel (a) of Figure \ref{['Fig3']}.