Dynamics of Solar Mesogranulation
Abstract
Using a 45.5-h time series of photospheric flow fields generated from a set of high-resolution continuum images (SOHO/MDI) we analyse the dynamics of solar mesogranule features. The series was prepared by Shine et al. (2000) applying a local correlation tracking algorithm with a 4.8 arcsec FWHM window. By computing 1-h running means in time steps of 10 minutes we generate 267 averaged divergence maps which are then segmented to obtain binary maps. A tracking algorithm then determines lifetimes and barycentre coordinates of regions of positive divergence defined as mesogranules (MGs). If we analyse features of lifetimes ≥1 h and areas ≥5 Mm2 we find a mean drift velocity of 304 ms, a mean travel distance of 2.5 Mm, a mean lifetime of 2.6 h, and a 1/e decay time of 1.6 h for a total of 2022 MGs. The advective motion of MGs within supergranules, which was found by Muller et al. (1992) and confirmed by Shine et al. (2000), is seen for half to two-thirds of the long-lived (≥4 h) MGs while the short-lived ones move irregularly. The results prove to be nearly independent of the divergence segmentation level.
- Publication:
-
Hvar Observatory Bulletin
- Pub Date:
- 2005
- Bibcode:
- 2005HvaOB..29...49L
- Keywords:
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- Convection;
- granulation;
- photosphere