Helioseismic Probing of Giant-Cell Flows Nicholas Featherstone Deborah Haber Brad Hindman Juri Toomre JILA / APS University of Colorado at Boulder

Searching for Giant Cells Convection on many scales: Granulation (~1 Mm, 1 km s -1 ) Mesogranulation (~5 Mm, 60 m s -1 ) Supergranulation (~30 Mm, 400 m s -1 ) Theory, simulations suggest another scale spanning solar CZ. SimulationsObservations Schou et al. 1998Miesch, et al (IP)

Mid CZ Upper CZ VrVr

Giant Cells: Possible Signatures VV Weak alignment of small-scale flows (Lisle et al. 2004) Large-scale longitudinal Variation of V 

Flow Field Analysis MDI Dynamics Program data from CR 1922MDI Dynamics Program data from CR 1922 Standard dense pack, tracked at Snodgrass rate.Standard dense pack, tracked at Snodgrass rate. 60 degrees in latitude centered about the solar equator.60 degrees in latitude centered about the solar equator. 4  x4  overlapping tiles with centers separated by 4  x4  overlapping tiles with centers separated by  Horizontal flow velocities calculated for each tile using f mode time-distance.Horizontal flow velocities calculated for each tile using f mode time-distance. Autocorrelation Time-DistanceAutocorrelation Time-Distance Spatial Separation (Mm) Time Lag (Min) Spatial Separation (Mm) Spatial Separation (Mm)

Horizontal Divergence Smoothed Divergence Maps Smoothing Scale: None Carrington Longitude (deg) Latitude (deg) Weak north-south alignment visible at smallest scales.Weak north-south alignment visible at smallest scales. Alignment becomes much more prominent at larger scalesAlignment becomes much more prominent at larger scales

Horizontal Divergence Smoothed Divergence Maps Smoothing Scale: 3  Carrington Longitude (deg) Latitude (deg) Weak north-south alignment visible at smallest scales.Weak north-south alignment visible at smallest scales. Alignment becomes much more prominent at larger scalesAlignment becomes much more prominent at larger scales

Horizontal Divergence Smoothed Divergence Maps Smoothing Scale: 5  Carrington Longitude (deg) Latitude (deg) Weak north-south alignment visible at smallest scales.Weak north-south alignment visible at smallest scales. Alignment becomes much more prominent at larger scalesAlignment becomes much more prominent at larger scales

Horizontal Divergence Smoothed Divergence Maps Smoothing Scale: 7  Carrington Longitude (deg) Latitude (deg) Weak north-south alignment visible at smallest scales.Weak north-south alignment visible at smallest scales. Alignment becomes much more prominent at larger scalesAlignment becomes much more prominent at larger scales

Measuring Alignment Longitudinal Avg Degrees Divergence Latitudinal Avg  lat = 1.4  lon = 0.89

128 0 Time Lag (min) Time Lag (min) Frame Rate Averaging Longitude (Deg) Day Prograde Strongly Prograde Strongly Retrograde

Variation with Frame Rate Carrington Longitude 210 : 270Carrington Longitude 270 :  lat Equatorial Frame Rate ( m s -1 ) Carrington Longitude 90 : 150 Carrington Longitude 170 : Equatorial Frame Rate ( m s -1 ) Equatorial Frame Rate ( m s -1 )  lat

Spatial Average Equatorial Frame Rate ( m s -1 )  lat

Conclusions Weak north-south alignment in horizontal divergence.Weak north-south alignment in horizontal divergence. Alignment persists at larger scales.Alignment persists at larger scales. Divergence features generally exhibit strongest north-south alignment with prograde tracking rates.Divergence features generally exhibit strongest north-south alignment with prograde tracking rates. We may be sensing the weak surface signal of giant-cell flows.We may be sensing the weak surface signal of giant-cell flows.

Peak Absent in  lonPeak Absent in  lon Tracking Velocity ( m s -1 )  lon