Time distance helioseismology is a valuable tool for examining near surface flow. It can produce vector maps of flows from the travel time of waves traversing subsurface ray paths. It has been demonstrated that time-distance helioseismology of the surface gravity waves can produce accurate surface maps of supergranulation. These maps average over the two megameters immediately below the surface (Duvall and Gizon, Solar Physics, 2000, in press). The temporal resolution of time-distance flow maps is large compared with the lifetime of small scale convection, but small compared with supergranule lifetimes. Therefore, it is possible to produce a time-series of time-distance flow maps which reveal patterns of supergranulation evolution. We have observed certain modes of supergranulation `birth' and `death' using time-distance helioseismology and have compared these with results from line-of-sight doppler velocities. This work was supported by the SOI-MDI NASA grant at Stanford and by the Solar Physics Branch of the Space Science Division of NASA.
AAS/Solar Physics Division Meeting #31
- Pub Date:
- May 2000