Multifractal Solar Euv Intensity Fluctuations and Their Implications for Coronal Heating Models

Abstract

We investigate the scaling properties of the long-range temporal evolution and intermittency of Atmospheric Imaging Assembly/Solar Dynamics Observatoryintensity observations in four solar environments: anactive region core, a weak emission region, and two core loops. We use two approaches: the probability distribution function (PDF) of time series incrementsand multifractal detrended fluctuation analysis (MF-DFA). Noise taints the results, so we focus on the 171 Å waveband, which has the highest signal-to-noise ratio. The lags between pairs of wavebands distinguish between coronal versus transition region (TR) emission. In all physical regions studied, scaling in the range of 15-45 minutes is multifractal, and the time series are anti-persistent on average. The degree of anti-correlation in the TR time series is greater than that for coronal emission. The multifractality stems from long-term correlations in the data rather than the wide distribution of intensities. Observations in the 335 Å waveband can be described in terms of a multifractal with added noise. The multiscaling of the extreme-ultraviolet data agrees qualitatively with the radiance from a phenomenological model of impulsive bursts plus noise, and also from ohmic dissipation in a reduced magnetohydrodynamic model for coronal loop heating. The parameter space must be further explored to seek quantitative agreement. Thus, the observational "signatures" obtained by the combined tests of the PDF of increments and the MF-DFA offer strong constraints thatcan systematically discriminate among models for coronal heating.

Multifractal analysis of the interstellar medium: first application to Hi-GAL observations

“…in studying turbulent flows). In astrophysics, it has been used, for example, in the study of the distribution of galaxies (Mandelbrot 1989;Borgani et al 1993;Pan & Coles 2000;de La Fuente Marcos & de La Fuente Marcos 2006), gamma-ray burst time series (Meredith et al 1995), and solar activity (Wu et al 2015;Cadavid et al 2016;Maruyama et al 2017).…”

Comparison of the Scaling Properties of EUV Intensity Fluctuations in Coronal Hole and Quiet-Sun Regions

“…This introduces correlations in the signals, which is at the center of what our analysis has uncovered. A more complex model based on impulsive heating by Pauluhn & Solanki (2007) was used to interpret the multiscaling properties of intensity fluctuations of the AIA 171 Å signals in an active region core and coronal loops (Cadavid et al 2016). In this case the intensity time series result from a sequence of "nanoflares" (exponential impulses as described above), which occur at each observational time step with a certain probability P f , a time scale T , and an amplitude E sampled from a power law distribution with scaling exponent α E > 2.…”

“…exponents for some turbulence models via a relation with the second-order structure function H = ξ(2)/2 (e.g.,Davies et al 1994). Some examples are: 0.33 (Kolmogorov), 0.35 (She-Leveque), 0.37 (Müller-Biskamp) Cadavid et al (2016). found that 171 Å emission in two hot coronal loops in an active region core had generalized Hurst exponents of 1.34 and 1.41 (H = 0.34, 0.41), which together with other diagnoses suggested a turbulent process.…”

Lagrangian Perspectives on the Small-scale Structure of Alfvénic Turbulence and Stochastic Models for the Dispersion of Fluid Particles and Magnetic Field Lines in the Solar Wind

“…Nevertheless, they are designed for providing an astute fitting scheme to turbulence data, and they all have indeed been successfully adapted and applied to solar wind turbulence (Bruno 2019). The multifractal phenomenology can also be applied for studying the radiation fields emitted by multiscale astrophysical objects observed at high resolution (Yahia et al 2021), including light emitted by the Sun in different energy ranges (Cadavid et al 2016). It is equally fruitful to use it in a Lagrangian perspective, in order to study the structure of the Lagrangian fields: the Eulerian fields evaluated along fluid particle trajectories.…”