Horizontal supergranule-scale motions inferred from TRACE ultraviolet observations of the chromosphere

Abstract

We study horizontal supergranule-scale motions revealed by TRACE observation of the chromospheric emission, and investigate the coupling between the chromosphere and the underlying photosphere. A highly efficient feature-tracking technique called balltracking has been applied for the first time to the image sequences obtained by TRACE (Transition Region and Coronal Explorer) in the passband of white light and the three ultraviolet passbands centered at 1700 Å, 1600 Å, and 1550 Å. The resulting velocity fields have been spatially smoothed and temporally averaged in order to reveal horizontal supergranule-scale motions that may exist at the emission heights of these passbands. We find indeed a high correlation between the horizontal velocities derived in the white-light and ultraviolet passbands. The horizontal velocities derived from the chromospheric and photospheric emission are comparable in magnitude. The horizontal motions derived in the UV passbands might indicate the existence of a supergranule-scale magnetoconvection in the chromosphere, which may shed new light on the study of mass and energy supply to the corona and solar wind at the height of the chromosphere. However, it is also possible that the apparent motions reflect the chromospheric brightness evolution as produced by acoustic shocks which might be modulated by the photospheric granular motions in their excitation process, or advected partly by the supergranule-scale flow towards the network while propagating upward from the photosphere. To reach a firm conclusion, it is necessary to investigate the role of granular motions in the excitation of shocks through numerical modeling, and future high-cadence chromospheric magnetograms must be scrutinized.

5 figures, accepted by Astronomy & Astrophysics

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• Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS observations
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• Properties of shock waves in the quiet Sun chromosphere
• Probing the Solar Atmosphere Using Oscillations of Infrared CO Spectral Lines
• Statistics of Photospheric Supergranular Cells Observed by SDO/HMI
• Tracing the magnetic field topology of the quiet corona using propagating disturbances
• Magnetic Influences on the Solar Wind (Ph.D. Dissertation)