Abstract
Supergranule revolution rate and lifetime can be measured by cross-correlating pairs of Doppler-velocity maps that have been filtered (by Hathaway's method) to remove other flows. As a conceptual framework for that analysis, this exploratory paper develops an idealized, phenomenological model of supergranule flows. Assumptions made about supergranule cells on the Sun's photosphere include: random location in space and time, and horizontal flows with circular symmetry and having a Simon–Weiss velocity function. Each supergranule is stable for a time, dies, and after a while, a daughter is born at a nearby position determined by a random walk. The effect on the cross-correlations of changing projection onto the line-of-sight as the Sun rotates is analyzed. The total cross-correlation for strips of constant latitude depends on two generic, slowly-varying projection functions. Effects of differential rotation and time-evolution are also considered. GONG observations of June 1994 show systematic variations in the width and shape of correlation peaks with latitude; our model suggests that projection effects alone can account for these without invoking any intrinsic variations of the supergranules.
Similar content being viewed by others
References
Gibson, E. G.: 1973, The Quiet Sun, NASA SP-303, 226.
Hathaway, D. H.: 1987, Solar Phys. 108, 1.
Hathaway, D. H.: 1988, Solar Phys. 117, 1.
Hathaway, D. H.: 1992, Solar Phys. 137, 15.
Scherrer, P. H., Wilcox, J. M., Svalgaard, L.: 1980, Astrophys. J. 241, 811.
Simon, G. W. and Weiss, N. O.: 1989, Astrophys. J. 345, 1060.
Smith, D.: 1998, J. Undergrad. Res. Phys. 16, 48.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Harman, S., Hrabik, T., Kasher, J. et al. A Simon–Weiss model for supergranule flows and their cross-correlations. Solar Physics 185, 227–254 (1999). https://doi.org/10.1023/A:1005161204481
Issue Date:
DOI: https://doi.org/10.1023/A:1005161204481