Abstract
Remote sensing of coronal and heliospheric periodicities can provide vital insight into the local conditions and dynamics of the solar atmosphere. We seek to trace long (one hour or longer) periodic oscillatory signatures (previously identified above the limb in the corona by, e.g., Telloni et al. in Astrophys. J.767, 138, 2013) from their origin at the solar surface out into the heliosphere. To do this, we combined on-disk measurements taken by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and concurrent extreme ultra-violet (EUV) and coronagraph data from one of the Solar Terrestrial Relations Observatory (STEREO) spacecraft to study the evolution of two active regions in the vicinity of an equatorial coronal hole over several days in early 2011. Fourier and wavelet analysis of signals were performed. Applying white-noise-based confidence levels to the power spectra associated with detrended intensity time series yields detections of oscillatory signatures with periods from 6 – 13 hours in both AIA and STEREO data. As was found by Telloni et al. (2013), these signatures are aligned with local magnetic structures. However, typical spectral power densities all vary substantially as a function of period, indicating spectra dominated by red (rather than white) noise. Contrary to the white-noise-based results, applying global confidence levels based on a generic background-noise model (allowing a combination of white noise, red noise, and transients following Auchère et al. in Astrophys. J.825, 110, 2016) without detrending the time series uncovers only sporadic, spatially uncorrelated evidence of periodic signatures in either instrument. Automating this method to individual pixels in the STEREO/COR coronagraph field of view is non-trivial. Efforts to identify and implement a more robust automatic background noise model fitting procedure are needed.
Highlights
The solar corona hosts a variety of dynamic phenomena that generate periodic and aperiodic variations in light intensity
What causes the variations in power-law index in neighbouring regions? If a “hump” is identified in the power model, can its appearance be attributed to a specific feature? Transient features have been shown to trigger kink oscillations in coronal loops: would these be identifiable above confidence or masked by the inclusion of the hump in background power? Our analysis suggests that deriving alternative noise models and parameter regimes may be necessary when studying different target regions or using different instruments
This study aimed to examine periodicities in intensity data using a multi-instrumental survey of magnetic structures associated with a specific active region extending out from the corona into the inner heliosphere
Summary
The solar corona hosts a variety of dynamic phenomena that generate periodic and aperiodic variations in light intensity. These signals are vital clues in our efforts to unlock the secrets of this enigmatic region of the Sun, providing insight into how dynamic phenomena contribute to both the coronal heating problem Signatures have been inferred across an enormous range of timescales, from the longest (and perhaps most famous) 11-year solar cycle variations down to periods of the order of minutes or even seconds (determined by current instrumental limits). The Solar Dynamics Observatory (SDO: Pesnell, Thompson, and Chamberlin, 2012) allows for continuous high-resolution and high-cadence measurements across a suite of instruments; this observatory has contributed significantly to studies of long-period oscillatory features in recent years. Examples include Smirnova et al (2013), who uncovered evidence of threeto seven-hour oscillatory periods using the Heliospheric and Magnetic Imager (HMI: Scherrer et al, 2012) onboard SDO, while Froment et al (2015) found four- to nine-hour periodic signatures using the Atmospheric Imaging Assembly (AIA: Lemen et al, 2012)
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