[Loops] Long-period pulsations in EUV loops: Fourier & wavelets analysis & evaporation / condensation cycles

[Frédéric Auchère]

Dear loop enthusiats,

Here are two papers recently published in ApJ that you might find of 
interest:

1. The first paper shows how to take into account the power-law nature 
of the power spectra of most solar intensity time-series in order to 
perform robust Fourier and wavelet analysis. It illustrates how data 
detending can lead to false positive detections. It also demonstrates 
that the white and red noise models built into the widely used wavelet 
code of Torrence & Compo cannot adequately represent the power spectra 
of coronal time series, thus also possibly causing false positives. It 
then gives practical details on how to use the Torrence & Compo code 
with custom pertinent noise models (including power-laws). Finally, we 
derive rigorous confidence levels taking account the total number of 
degrees of freedom in the wavelet spectra.

https://ui.adsabs.harvard.edu/#abs/2016ApJ...825..110A/abstract

2. We recently detected numerous pulsations of long-period (hours) in 
coronal loops (Auchère et al 2014 
https://ui.adsabs.harvard.edu/#abs/2014A&A...563A...8A/abstract). Using 
Fourier and wavelet analysis, we demonstrate that the observed periodic 
signals are not signatures of vibrational modes. Instead, superimposed 
on the power law expected from the stochastic background emission, the 
power spectra of the time series exhibit the discrete harmonics and 
continua expected from periodic trains of pulses of random amplitudes. 
These characteristics reinforce our earlier interpretation of these 
pulsations as being cycles of evaporation / condensation.

https://ui.adsabs.harvard.edu/#abs/2016ApJ...827..152A/abstract

Best regards,

Frédéric Auchère