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

Author : Thierry Roudier (IRAP)

Contacts: Thierry Roudier (thierry.roudier/at/ & Martine Chane-Yook (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.

- Version 1.0 (November 2019) : 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.

- Version 1.1 (April 2020) : what is new compared to previous release is that IDL codes from step 3 are combined into one sigle IDL file. Furthermore, input file (param_seq_) and step 1 to 3 describing CST codes are explained in details in the documentation (see section 6 and 3). An automatic way to take HMI data from JSOC is proposed (see section 4 of the documentation) by T. Corbard (OCA). Click on the following links to download the package source file, the QUICKSTART guide and 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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