AAS 200th meeting, Albuquerque, NM, June 2002
Session 38. Solar Photosphere, Chromosphere and Transition Region
Display, Tuesday, June 4, 2002, 10:00am-6:30pm, SW Exhibit Hall

## [38.05] Mesogranulation from Principal Component Analysis of SVST Photospheric Continuum Images

E. Bell, A. C. Cadavid, J. K. Lawrence (Calfornia State University, Northridge), T. E. Berger (Lockheed Martin Space and Astrophysics Laboratory)

We analyze a sequence of 279 images of the photosphere made with the Swedish Vacuum Solar Telescope on 1997 June 11. The sequence spans 3 hr with cadence 38 s. The images were taken in continuum near 4364 Å, and underwent phase diversity reconstruction. Resolution is ~ 0.2 Mm and field of view 32 X 32 Mm.

We carried out a principal component analysis on sequences of 15 images spaced 6 min apart and covering 1.5 hr. The 15 X 15 correlation matrix of each such set of images was diagonalized, giving 15 eigenimages which are linear combinations of the original 15. The eigenimage corresponding to the largest eigenvalue is the linear combination that best resembles the original set as a whole; those with smaller and smaller eigenvalues resemble the overall set less and less well. Fourier spectra of the eigenimages were calculated separately for several sequences and then averaged together to reduce uncertainties.

Fourier analysis of the leading eigenimage reveals structure at two scales: one for \lambda =1/\nu ~1.5 Mm corresponding to granulation and another for \lambda ~ 4.5 Mm. Because of their scale and because the time span of the sets lies between the lifetimes of granules and mesogranules, we interpret the latter as mesogranules. The subsequent eigenimages do not show the larger structure, but show the granular peak at successively smaller scales. This indicates a spatio-temporal scaling of the granulation with shorter lifetimes for smaller features. For comparison purposes, simulated granulation images (Cattaneo, Lenz and Weiss 2001) were similarly analyzed and give similar results. Work supported in part by grants NSF-ATM-9987305, NASA-NAG5-10880 and the NASA CSUN/JPL PAIR Program.

F. Cattaneo, D. Lenz and N. Weiss 2001, ApJ, 563, L91.