O VI 1032 Å intensity and Doppler shift oscillations above a coronal hole: Magnetosonic waves or quasi-periodic upflows?

Mancuso, Salvatore; Raymond, J. C.; Rubinetti, Sara; Taricco, Carla

doi:10.1051/0004-6361/201628769

Cited by 9 publications

(8 citation statements)

References 22 publications

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“…At heights 1.4 R ⊙ , there have been studies using the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO). Using an O vi line at 1.4 R ⊙ , Mancuso et al (2016) found intensity oscillations with periods of ∼ 20 minutes and amplitudes of ∆I/I ≈ 10% (∆n e /n e ≈ 5%). It is interesting that these large amplitudes, similar to those found near the limb, were found at such large heights as dissipation is expected to reduce acoustic wave amplitudes as the waves propagate (Ofman et al 1999(Ofman et al , 2000.…”

Section: Introductionmentioning

confidence: 98%

Density Fluctuations in a Polar Coronal Hole

Hahn

D’Huys

Savin

2018

ApJ

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We have measured the root-mean-square (RMS) amplitude of intensity fluctuations, ∆I, in plume and interplume regions of a polar coronal hole. These intensity fluctuations correspond to density fluctuations. Using data from the (SWAP) on Project for Onboard Autonomy (Proba2), our results extend up to a height of about 1.35 R ⊙ .One advantage of the RMS analysis is that it does not rely on a detailed evaluation of the power spectrum, which is limited by noise levels to low heights in the corona. The RMS approach can be performed up to larger heights where the noise level is greater, provided that the noise itself can be quantified. At low heights, both the absolute ∆I, and the amplitude relative to the mean intensity, ∆I/I, decrease with height. However, starting at about 1.2 R ⊙ ∆I/I increases, reaching 20-40% by 1.35 R ⊙ . This corresponds to density fluctuations of ∆n e /n e ≈ 10-20%. The increasing relative amplitude implies that the density fluctuations are generated in the corona itself. One possibility is that the density fluctuations are generated by an instability of Alfvén waves. This

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Section: Introductionmentioning

confidence: 98%

Density Fluctuations in a Polar Coronal Hole

Hahn

D’Huys

Savin

2018

ApJ

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“…Over the last few decades, a technique called singular spectral analysis (SSA;Vautard & Ghil 1989) and its multivariate extension (MSSA; Ghil et al 2002) have been widely used in the identification of oscillations in climatic time series (e.g., Taricco et al 2015ab). Recently, this technique has been successfully applied in the analysis of Doppler shift oscillations in the UV corona (Mancuso et al 2015(Mancuso et al , 2016. One of the main advantages of MSSA with respect to classical Fourier methods is its ability to detect common non-sinusoidal oscillations that are modulated both in amplitude and phase so that the original signals are no more simply decomposed into periodic sinusoidal functions but into data-adaptive waves.…”

Section: Analysis and Preliminary Resultsmentioning

confidence: 99%

Multivariate analysis of intermediate periodicities of the green corona

Mancuso¹,

Lee

Taricco

et al. 2018

Proc. IAU

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Solar activity is observed to fluctuate with time, undergoing a wide range of periodicities from minutes up to thousands of years as evinced from proxies based on cosmogenic isotopes. In this work, we apply Multichannel Singular Spectrum Analysis (MSSA), a data-adaptive, multivariate technique that simultaneously exploits the spatial and temporal correlations of the input data to extract common modes of variability to investigate the intermediate quasi-periodicities of the green coronal emission line at 530.3 nm for the period between 1944 and 2008. A preliminary MSSA analysis confirms the presence of significant quasi-biennial oscillations in the data with amplitude varying significantly with time and latitude. On the other hand, a clear North-South asymmetry is observed both in their intensity and period distribution.

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“…The original time-evolving signal is not simply decomposed into periodic sinusoidal functions as in Fourier-like techniques, but broken down into data-adaptive waves that can be modulated both in amplitude and phase. Although not commonly used in astrophysical contexts, this powerful technique has recently been applied to successfully detect Doppler-shift oscillations in the UV corona (Mancuso & Raymond 2015;Mancuso et al 2016), analyze quasi-biennial oscillations of the Fe xiv green coronal emission line at 5303 Å (Mancuso et al 2018), and, more recently, to detect multiple quasi-periodic pulsations observed during the flaring activity of a young, active solar-type star observed by the Kepler mission (Mancuso et al 2020). Its multivariate extension, the so-called multichannel singular spectrum analysis (MSSA), has the additional ability to identify coherent space-time patterns and thus extract common periodic signals, trends and noise from a multivariate dataset (e.g., Taricco et al 2015;Mancuso et al 2018).…”

Section: Multichannel Singular Spectrum Analysismentioning

confidence: 99%

Differential rotation of the solar corona: A new data-adaptive multiwavelength approach

Mancuso

Giordano

Barghini

et al. 2020

A&A

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Context. The characterization of the differential rotation of the extended corona is still lacking conclusive results about the actual rotation rate profiles, and it is also expected to vary along the solar cycle. While some studies supported the quasi-rigidity of coronal rotation, others have found evidence of differential rotation to occur. Aims. For the purpose of investigating the differential rotation of the solar corona, we analyzed ultraviolet (UV) spectral line observations acquired on both the east and west limbs at 1.7 R⊙ by the Ultraviolet Coronagraph Spectrometer (UVCS) on-board the Solar and Heliospheric Observatory during the solar minimum preceding solar cycle 23. To obtain a reliable and statistically robust picture of the rotational profile, we used a set of simultaneous 400 day long spectral line intensities of five different spectral lines: O VI 1032 Å, O VI 1037 Å, Si XII 499 Å, Si XII 521 Å, and H I Lyα 1216 Å, which are routinely observed by UVCS. Methods. The data were analyzed by means of two different techniques: the generalized Lomb-Scargle periodogram and a multivariate data-adaptive technique called multichannel singular spectrum analysis. Among many other positive outcomes, this latter method is unique in its ability to recognize common oscillatory modes between the five time series observed at both limbs. Results. The latitudinal rotation profile obtained in this work emphasizes that the low-latitude region of the UV corona (about ±20° from the solar equator) exhibits differential rotation, while the higher-latitude structures do rotate quasi-rigidly. Moreover, in contrast to previous results obtained using only O VI 1032 Å data over a 365 day time interval during solar minimum activity, the alleged north-south rotational asymmetry of the UV corona, if existent, is much less pronounced. Conclusions. The differential rotation rate of the solar corona as evinced at low-latitudes is consistent with the rotational profile of the near-surface convective zone of the Sun, suggesting that the rotation of the corona at 1.7 R⊙ is linked to intermediate-scale magnetic bipole structures anchored near 0.99 R⊙. The quasi-rigid rotation rate found at mid and high latitudes is instead attributed to the influence of large-scale coronal structures linked to the rigidly rotating coronal holes. We further suggest that the methodology presented in this paper could represent a milestone for future investigations on differential rotation rates when dealing with simultaneous multiwavelength data.

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O VI 1032 Å intensity and Doppler shift oscillations above a coronal hole: Magnetosonic waves or quasi-periodic upflows?

Cited by 9 publications

References 22 publications

Density Fluctuations in a Polar Coronal Hole

Density Fluctuations in a Polar Coronal Hole

Multivariate analysis of intermediate periodicities of the green corona

Differential rotation of the solar corona: A new data-adaptive multiwavelength approach

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