Abstract
Abstract We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca ii 8542 Å and Hα lines as well as in the photospheric Fe i line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca ii and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave.
Highlights
Solar tornadoes have been observed in the solar atmosphere for nearly a century
This study focuses on small-scale chromospheric swirls (Wedemeyer-Böhm & Rouppe van der Voort 2009) that have heights between 2 and 3 Mm and diameters between 1 and 3 Mm
Instruments such as the CRisp Imaging Spectro-Polarimeter (CRISP; Scharmer et al 2008) on the Swedish 1 m Solar Telescope (SST; Scharmer et al 2003) equipped with adaptive optics have advanced to the extent that it has become routinely possible to observe vortices on much smaller scales ( 1 Mm wide), and their evolution is close to the telescope’s diffraction limit
Summary
Solar tornadoes have been observed in the solar atmosphere for nearly a century. Their importance lies in how they act as energy channels between different layers of the solar atmosphere (Zöllner 1869; Hale 1908a, 1908b; Parker 1983; Simon & Weiss 1997; Brown et al 2003; Wedemeyer-Böhm et al 2012, and references therein). Spatial resolutions can be achieved that are below the mean free path of photons, which, in the solar photosphere and chromosphere, is typically between 70 and 120 km. At such scales, one can study the evolution of photospheric granules and magnetic. Wedemeyer-Böhm et al (2012) observed chromospheric swirls in Ca II (8542 Å) They found Doppler velocities of 4 km s−1 and evidence of an increase in swirl cross section with height, implying a “magnetic tornado.”.
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