Exploring mutual information between IRIS spectral lines. I. Correlations between spectral lines during solar flares and within the quiet Sun

Abstract

Spectral lines allow us to probe the thermodynamics of the solar atmosphere, but the shape of a single spectral line may be similar for different thermodynamic solutions. Multiline analyses are therefore crucial, but computationally cumbersome. We investigate correlations between several chromospheric and transition region lines to restrain the thermodynamic solutions of the solar atmosphere during flares. We used machine-learning methods to capture the statistical dependencies between 6 spectral lines sourced from 21 large solar flares observed by NASA's Interface Region Imaging Spectrograph (IRIS). The techniques are based on an information-theoretic quantity called mutual information (MI), which captures both linear and nonlinear correlations between spectral lines. The MI is estimated using both a categorical and numeric method, and performed separately for a collection of quiet Sun and flaring observations. Both approaches return consistent results, indicating weak correlations between spectral lines under quiet Sun conditions, and substantially enhanced correlations under flaring conditions, with some line-pairs such as Mg II and C II having a normalized MI score as high as 0.5. We find that certain spectral lines couple more readily than others, indicating a coherence in the solar atmosphere over many scale heights during flares, and that all line-pairs are correlated to the GOES derivative, indicating a positive relationship between correlation strength and energy input. Our methods provide a highly stable and flexible framework for quantifying dependencies between the physical quantities of the solar atmosphere, allowing us to obtain a three-dimensional picture of its state.

References in corpus (20)

• The Interface Region Imaging Spectrograph (IRIS)
• An Observational Overview of Solar Flares
• Equitability, mutual information, and the maximal information coefficient
• The formation of IRIS diagnostics I. A quintessential model atom of Mg II and general formation properties of the Mg II h&k lines
• Spectral signatures of chromospheric condensation in a major solar flare
• Identifying typical Mg II flare spectra using machine learning
• The formation of IRIS diagnostics V. A quintessential model atom of C II and general formation properties of the C II lines at 133.5 nm
• Si IV Resonance Line Emission During Solar Flares: Non-LTE, Non-equilibrium, Radiation Transfer Simulations
• IRIS Observations of the Mg II h & k Lines During a Solar Flare
• Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
• IRIS observations of short-term variability in moss associated with transient hot coronal loops
• A parameter study for modeling MgII h and k emission during solar flares
• Three-dimensional modeling of chromospheric spectral lines in a simulated active region
• The Formation of IRIS Diagnostics. VII. The Formation of the OI 135.56 nm Line in the Solar Atmosphere
• Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations
• Real-time flare prediction based on distinctions between flaring and non-flaring active region spectra
• Non-LTE inversions of a confined X2.2 flare: I. Vector magnetic field in the photosphere and chromosphere
• The potential of many-line inversions of photospheric spectropolarimetric data in the visible and near UV
• Modeling Mg II during Solar Flares. II. Non-equilibrium Effects
• Statistical Study of Chromospheric Evaporation in Impulsive Phase of Solar Flares

Cited by in corpus (9)

• Solar Flare Ribbon Fronts I: Constraining flare energy deposition with IRIS spectroscopy
• Identifying preflare spectral features using explainable artificial intelligence
• Occurrence and Statistics of IRIS Bursts
• Exploring mutual information between IRIS spectral lines. II. Calculating the most probable response in all spectral windows
• Using Multiple Instance Learning for Explainable Solar Flare Prediction
• Designing wavelength sampling for Fabry-Pérot observations. Information-based spectral sampling
• Investigating datasets with high IRIS burst prevalence
• IRIS burst properties in active regions
• Specialist Discussion Meeting: 3D structure of the flare chromosphere