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Applying 2D motion magnification to EUV observations of the low-amplitude kink oscillations

This page is online version of my poster on RADIOSUN-5 workshop and Summer school.


We introduce a new approach for the investigation of the low-amplitude transverse oscillations of coronal loops recently discovered in SDO/AIA data. Typical amplitude of these oscillation is found to be about 0.2 Mm, that is less than SDO/AIA pixel size. Measuring parameters of such a small motion is a challenging task. The technique called motion magnification can help here and simplify the analysis. Motion magnification acts like a microscope for low amplitude motions in image sequences (i.e. data cubes). It artificially amplifies small displacements making them much better visible in time-distance plots and animations. This approach is found to give good results for harmonic oscillations, including the modulated signals, such as exponentially decaying, multi-modal and frequency modulated signals. The method was tested on an artificial data set, and using the EUV observations of a non-flaring active region, clearly demonstrating the presence of low-amplitude decay-less oscillations in the majority of coronal loops associated with the active region.

Method description

  1. Input: a sequence of 2D images (data cube)
  2. Compute spatial 2D dual tree complex wavelet transform (DTℂWT) of each image
  3. Calculate slow trend of DTℂWT components phases by smoothing them along the time dimension
  4. Magnify phase variation of DTℂWT components
  5. Reconstruct output images using inverse DTℂWT
  6. Output: a data cube with magnified transverse motions

Testing on an artificial model

The method has been tested on a sequence of artificial images, imitating typical kinds of kink oscillations in a system of four loops.

Loop 1: harmonic oscillation with constant period and amplitude.

Loop 2: decay-less oscillation in an expanding loop. Period is changing in time.

Loop 3: exponentially decaying standing oscillation

Loop 4: coexistence of two harmonics, global mode and third harmonic.

The built-in oscillations are clearly visible in the processed data for all four kinds of the kink oscillatory patterns that are difficult to see in the original data.

Testing on the artificial model

Testing on SDO/AIA data

The developed method was tested on the SDO/AIA 171 Å observations of a coronal loop bundle previously analysed by Nistico, Anfinogentov, and Nakariakov (2014). This set of coronal loops was observed by SDO/AIA on the south-western limb of the Sun on 21 January 2013 and was not associated with any NOAA active region. In the original time-distance plot, the low amplitude oscillations could only be noticed by an experienced eye knowing where and when to look at. But, even a small motion magnification by a factor of 3 makes the oscillatory patterns visible to everyone without difficulty. Larger magnification (×9) allows one to investigate oscillatory profiles in detail, revealing possible amplitude evolution and coexistence of multiple harmonics.

Testing on the SDO/AIA data