Measure of Solar surface velocities from granule tracking: Coherent Structure Tracking (CST) algorithm

Author : Thierry Roudier (IRAP)

Contacts: thierry.roudier/at/, martine.chane-yook/at/

  • Purpose:

We propose a set of codes written in IDL and Fortran, computing the horizontal velocity field on the Sun surface by using solar granules as tracers. CST codes take as input HMI/SDO intensity images with a time step of 45s. We use also the HMI/SDO Dopplergrams.

  • More informations:

- Roudier, 2012, A&A, 540, A88

- Svanda, 2013, the Astrophysical Journal, 771:32

- Roudier, 2013, A&A, 552, A113

- Rincon, 2017, A&A, 599, A69

- Roudier, 2018, A&A, 611, A92

More references about small velocity fields:

- Roudier, 1999, Astron. Astrophys., 349, 301-311

- Rieutord, 2001, A&A, 377, L14-L17

- Rieutord, 2007, A&A, 471, 687-694

- Tkaczuk, 2007, A&A, 471, 695-703

  • Fortran files and documentations:

CST codes were successfully tested on clusters running linux with ifort compiler and SSWIDL. The source codes are available here : CST_V1.0. For running the code, see the QUICKSTART guide. For more details on the codes, see the documentation.

  • Output files (test case):

- image of the full Sun (October 21, 2010) : Solar segmented granules that are followed in time to get the horizontal velocities on all the Sun surface.

- image of the disc center (October 21, 2010) : Solar segmented granules visible at the disc center of Sun at high resolution

- image of the limb (October 21, 2010) : Solar segmented granules visible at the limb of Sun at high resolution. A Sunspot location is visible in the top left part of the image.

A workshop is dedicated to the training and use of the Coherent Structure Tracking (CST) software. It will take place on March 3-4, 2020 at IAS in Orsay, France. This workshop is open to all researchers and students of the international solar community, and is free but registration is mandatory before February, 29, 2020.

- Workshop website:

- Presentation by Thierry Roudier

- Limbshift, Beckers & Nelson, Solar Physics, Vol 58, Issue 2, pp. 243-261, 1978

- References on different methods of measuring surface movements

- Presentation by Martine Chane-Yook



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