Interface Region Imaging Spectrograph (IRIS) Observations of the Fractal Dimension in the Solar Atmosphere |
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Markus J. Aschwanden Submitted: 2022-07-21 10:31
While previous work explored the fractality and self-organized criticality
(SOC) of flares and nanoflares in wavelengths emitted in the solar corona (such
as in hard X-rays, soft X-rays, and EUV wavelenghts), we focus here on
impulsive phenomena in the photosphere and transition region, as observed with the
Interface Region Imaging Spectrograph (IRIS) in the temperature range of
Te ≈ 104-106 K. We find the following fractal dimensions (in increasing
order): D_A=1.21 ± 0.07 for photospheric granulation,
D_A=1.29 ± 0.15 for plages in the transition region,
D_A=1.54 ± 0.16 for sunspots in the transition region,
D_A=1.59 ± 0.08 for magnetograms in active regions,
D_A=1.56 ± 0.08 for EUV nanoflares,
D_A=1.76 ± 0.14 for large solar flares, and up to
D_A=1.89 ± 0.05 for the largest X-class flares.
We interpret low values of the fractal dimension
(1.0 ≈ D_A ≈ 1.5)
in terms of sparse curvi-linear flow patterns, while high values
of the fractal dimension (1.5 ≈ D_A ≈ 2.0)
indicate near space-filling transport processes, such as
chromospheric evaporation. Phenomena in the solar transition
region appear to be consistent with SOC models, based on
their size distributions of fractal areas A and (radiative) energies E,
which show power law slopes of α _Aobs=2.51 ± 0.21
(with α _Atheo=2.33 predicted), and α _Eobs=2.03 ± 0.18
(with α _Etheo=1.80 predicted).
Authors: Markus J. Aschwanden and Nived Vilangot Nhalil
Projects: None
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Publication Status: Frontiers in Astronomy and Space Sciences (subm. 2022 Jul 21)
Last Modified: 2022-07-27 10:13
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