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Proposing new ways to analyze the resolved shape changes of photospheric bright points as wave drivers

Presentation #328.16 in the session “Solar Physics Division (SPD): Simulations, Magnetic Fields, and Coronal Structure and Heating”.

Published onJun 18, 2021
Proposing new ways to analyze the resolved shape changes of photospheric bright points as wave drivers

Magnetic bright points on the solar photosphere, prominent in the G band but also visible in the continuum, mark the footpoints of kilogauss magnetic flux tubes extending toward the corona. The horizontal motions of these footpoints, driven by convective buffeting, are believed to excite MHD waves which propagate to the corona, where they deposit heat through turbulent dissipation. Measuring these motions observationally can thus constrain MHD-wave energy transport and provide a key lower boundary condition in coronal and heliospheric models. At ~100 km in diameter, most bright points are currently unresolved. Tracking bright-point centroids has been a mainstay analysis technique, and it allows the modeling of kink-mode wave excitation in the overlying flux tubes. First-light images from DKIST have resolved the sizes and shapes of bright points, and the coming science operations will reveal the time evolution of these high-resolution details, which is expected to excite sausage-mode and higher-order flux-tube waves. We propose two complementary ways to take the “next step” beyond centroid tracking and account for these additional wave modes, and we demonstrate these techniques on MURaM simulated images of DKIST-like resolution as a proof-of-concept. In the first technique, we describe each bright point with a centroid location as well as the parameters of an ellipse fitted to the bright point’s shape. We derive expressions for the energy flux of n=0, 1, and 2 wave modes in terms of the evolution of these parameters. In the second approach, we use an off-the-shelf algorithm for computing the earth mover’s distance to infer a horizontal velocity field responsible for shifting a bright point from one shape to the next, under an assumed advective and planar process. Despite the simplicity of this approach, we find some agreement with the “ground truth” plasma velocities in the MURaM simulation. These velocity fields can then be used to estimate energy fluxes. We present estimated wave energy fluxes from both of these approaches. These fluxes are non-negligible, suggesting these wave modes are a worthy target for observational study and motivating further development of these and other techniques, all of which can provide new constraints for wave-based models of coronal heating.

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