HR: 16:15h
AN: SP24A-04 [Abstracts]
TI: Do Supergranules Tend to Align in the North-South Direction?
AU: * Zhao, J
EM: junwei@quake.stanford.edu
AF: Hansen Experimental Physics Laboratory, Stanford University, 455 via Palou, Stanford, CA 94305-4085 United States
AU: Gizon, L
EM: gizon@quake.stanford.edu
AF: Hansen Experimental Physics Laboratory, Stanford University, 455 via Palou, Stanford, CA 94305-4085 United States
AU: Gizon, L
EM: gizon@quake.stanford.edu
AF: MPI Sonnensystemforschung, Max-Planck-Str. 2, Katlenburg-Lindau, 37191 Germany
AB:
We investigate the recent claim by Lisle, Rast, and Toomre (2004, ApJ) that supergranules tend to align preferentially in the north-south direction. We repeat their analysis with
an extensive set of maps of the horizontal divergence of flow fields derived from time-distance helioseismology. We construct temporal averages of the divergence maps for different east-west tracking velocities (vx) and measure the rms values in
the east-west (σx) and north-south (σy) directions from these maps. In agreement with Lisle et al. (2004) we
find that, near the equator, the ratio σx/σy is maximum (and greater than one) for a tracking velocity 120 m/s
above the Carrington velocity. In addition, we find that σx/σy displays a second local maximum at a tracking
rate close
to the Carrington velocity. We argue that the variations of the ratio σx/σy as a function of vx is a direct
consequence and additional evidence of the wavelike power spectrum of
supergranulation observed by Gizon, Duvall, and Schou (2003, Nature). Thus, a north-south alignment of supergranules is not
the only explanation nor a necessary condition for a ratio σx/σy greater than one. Additionally, we also study
the variations of
the ratio σy/σx as a function of north-south velocity
shifts (vy), and find that the ratio σy/σx also has
two maxima of similar amplitude separated by approximately 120 m/s.
DE: 7522 Helioseismology
DE: 7529 Photosphere
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly