Above the Noise: The Search for Periodicities in the Inner Heliosphere.

Area of Science:

• Solar Physics
• Heliophysics
• Plasma Physics

Background:

• Remote sensing of solar atmosphere periodicities provides crucial data on local conditions and dynamics.
• Previous studies identified long periodic oscillatory signatures in the solar corona above the limb.

Purpose of the Study:

• To trace long-period (≥1 hour) oscillatory signatures from the solar surface into the heliosphere.
• To investigate the evolution of active regions near an equatorial coronal hole using multi-spacecraft data.

Main Methods:

• Combined on-disk observations from the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA).
• Concurrent extreme ultra-violet (EUV) and coronagraph data from the Solar Terrestrial Relations Observatory (STEREO).
• Fourier and wavelet analysis of intensity time series, with white-noise-based and global background noise models.

Main Results:

• Detections of 6–13 hour oscillatory signatures aligned with local magnetic structures using white-noise confidence levels on detrended data.
• Substantial variation in spectral power densities indicates spectra dominated by red noise.
• Global confidence levels on non-detrended data revealed only sporadic, uncorrelated periodic signatures.

Conclusions:

• Solar surface magnetic structures host long-period oscillations that propagate into the heliosphere.
• The choice of noise model and data detrending significantly impacts the detection of these periodic signatures.
• Developing robust automatic background noise modeling for coronagraph data is essential for future analysis.