Automated Detection of Chromospheric Swirls Based on Their Morphological Characteristics

Dakanalis, Ioannis; Tsiropoula, G.; Tziotziou, K.; Koutroumbas, Konstantinos

doi:10.1007/s11207-020-01748-3

Cited by 9 publications

(9 citation statements)

References 43 publications

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“…The derivation of high point density areas formed by highly-curved features was recently implemented in a solar physical context by Dakanalis et al. ( 2021 ). They developed an automated chromospheric swirl detection method to exploit the spiral-like observational signatures of plasma motions in the higher layers of the solar atmosphere (e.g., observations in the spectral line core of and Ca ii 8542 Å).…”

Section: Detection Methodsmentioning

confidence: 99%

Vortex Motions in the Solar Atmosphere

et al. 2023

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Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in $\text{H}\alpha $ H α , innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions.

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Section: Detection Methodsmentioning

confidence: 99%

Vortex Motions in the Solar Atmosphere

et al. 2023

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“…In this paper, we attempt to detect the existing swirls in the entire FoV in a time series of highresolution, high-cadence Hα observations and extract statistical information for a number of critical physical parameters of these structures. The detection was performed via an automated detection method of chromospheric swirls presented by Dakanalis et al (2021) (hereafter Paper I) which exploits the morphological characteristics of the observational signature of swirling motions in the layer of the chromosphere. The rest of the paper is organized as follows: in Section 2, the set of observations used in the present analysis is described.…”

Section: Introductionmentioning

confidence: 99%

Chromospheric swirls

Dakanalis

Tsiropoula

Tziotziou

et al. 2022

A&A

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Context. Chromospheric swirls are related to convectively driven vortex flows and considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties. Aims. We aim to detect and track chromospheric swirls both in space and time by applying a newly developed novel automated method on high quality time series of Hα observations and to conduct a statistical analysis to determine their properties. Methods. We applied a recently developed automated chromospheric swirl detection method to time-series observations of a quiet region of the solar chromosphere obtained in the Hα-0.2 Å wavelength of the Hα spectral line by the CRISP instrument at the Swedish 1-m Solar Telescope. The algorithm exploits the morphological characteristics of swirling events in high contrast chromospheric observations and results in the detection of these structures in each frame of the time series and their tracking over time. We conducted a statistical analysis to determine their various properties, including a survival analysis for deriving the mean lifetime. Results. A mean number of 146 ± 9 swirls was detected within the Hα-0.2 Å field of view at any given time. The mean surface density is found equal to ∼0.08 swirls Mm −2 and the occurrence rate is ∼10 −2 swirls Mm −2 min −1 . These values are much higher than those previously reported from chromospheric observations. The radii of the detected swirls range between 0.5 and 2.5 Mm, with a mean value equal to 1.3 ± 0.3 Mm, which is slightly higher than previous reports. The lifetimes range between 1.5 min and 33.7 min (equal to the duration of the observations) with an arithmetic mean value of ∼8.5 min. A survival analysis of the lifetimes, however, using the Kaplan-Meier estimator in combination with a parametric model results in a mean lifetime of 10.3 ± 0.6 min. Conclusions. Swirls are ubiquitous in the solar chromosphere. An automated method sheds more light on their abundance than visual inspection, while higher cadence, higher resolution observations will most probably result in the detection of a higher number of such features on smaller scales and with shorter lifetimes.

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“…Each cluster represents a vortex, for which one can compute different properties. A similar approach has been adopted by Dakanalis et al (2021) to automatically identify vortices from clusters of curved streamlines.…”

Section: Clustering Methodsmentioning

confidence: 99%

“…Silva et al (2018) presented a comparison between the swirling strength, the Γ functions, and the LAVD criteria on horizontal velocity fields extracted from observations. An alternative approach has been put forward by Dakanalis et al (2021) as they identify vortices directly from chromospheric filtergrams using the morphological winding-angle method.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the identification of the vortex center and boundaries, which is needed for a proper study of vortex dynamics and interaction, can be obtained with the Γ functions and the LAVD/IVD methods only. In principle, the morphological method presented by Dakanalis et al (2021) should be the preferred method because it takes the large-scale properties of the flow into account, but it is not well-suited for the analysis of numerical simulations.…”

Section: Introductionmentioning

confidence: 99%

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Innovative and automated method for vortex identification

Cuissa

Steiner

2022

A&A

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Context. A universally accepted definition of what a vortex is has not yet been reached. Therefore, we lack an unambiguous and rigorous method for the identification of vortices in fluid flows. Such a method would be necessary to conduct robust statistical studies on vortices in highly dynamical and turbulent systems, such as the solar atmosphere. Aims. We aim to develop an innovative and robust automated methodology for the identification of vortices based on local and global characteristics of the flow. Moreover, the use of a threshold that could potentially prevent the detection of weak vortices in the identification process should be avoided. Methods. We present a new method that combines the rigor of mathematical criteria with the global perspective of morphological techniques. The core of the method consists in the estimation of the center of rotation for every point of the flow that presents some degree of curvature in its neighborhood. For that, we employ the Rortex criterion and combine it with morphological considerations of the velocity field. We then identify coherent vortical structures by clusters of estimated centers of rotation. Results. We demonstrate that the Rortex is a more reliable criterion than are the swirling strength and the vorticity for the extraction of physical information from vortical flows, because it measures the rigid-body rotational part of the flow alone and is not biased by the presence of pure or intrinsic shears. We show that the method performs well on a simplistic test case composed of two Lamb-Oseen vortices. We combine the proposed method with a state of the art clustering algorithm to build an automated vortex identification algorithm. The algorithm is applied to an artificial flow composed of multiple Lamb-Oseen vortices with a random noisy background and to the turbulent flow of a simulated magneto-hydrodynamical Orszag-Tang vortex test. The results demonstrate the reliability and accuracy of the method. A Python implementation of the algorithm is publicly available. Conclusions. The present automated vortex identification method can be considered a new tool for the detection and study of vortices in dynamical and turbulent (magneto-)hydrodynamical flows. By applying the implemented algorithm to numerical simulations and observational data, and by comparing it to existing detection methods, we seek to successively improve the reliability of the detections and, ultimately, our knowledge on swirling motions in the solar, stellar, and planetary atmospheres.

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Automated Detection of Chromospheric Swirls Based on Their Morphological Characteristics

Cited by 9 publications

References 43 publications

Vortex Motions in the Solar Atmosphere

Vortex Motions in the Solar Atmosphere

Chromospheric swirls

Innovative and automated method for vortex identification

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