Previous abstract Next abstract

Session 35 - Solar Magnetic Fields.
Display session, Tuesday, June 11
Tripp Commons,

[35.07] Vector Magnetic Fields and the Evershed Flow in Sunspots

D. C. H. Stanchfield II, J. H. Thomas (U. Rochester), B. W. Lites (HAO/NCAR)

We present results of simultaneous observations of the vector magnetic field and the Evershed effect in two sunspots, made with the Advanced Stokes Polarimeter at the Vacuum Tower Telescope at NSO (Sacramento Peak). The vector magnetic field is determined from the Stokes profiles of the magnetically sensitive line Fe I 630.25, and Doppler velocities are measured in several lines including the weak C I 538.03 line, formed in the deepest layers of the atmosphere. In addition to maps of the vector magnetic field and the line-of-sight Doppler velocity, we present maps of the true flow speed assuming that the flow is everywhere aligned with the magnetic field. The results confirm the recent discovery by Rimmele (1995), that the Evershed flow is generally confined to narrow, elevated channels in the penumbra. In the Fe I 537.96 line (formed at a height of about 230 km) we see isolated, radially elongated channels of Evershed flow in the outer penumbra. These flow channels lie in regions of the penumbra where the magnetic field is most nearly horizontal. In the C I line (formed at a height of about 40 km) the flow pattern shows small, isolated patches of upflow lying at the inner end of the Fe I flow channels, where the magnetic field is more highly inclined to the horizontal. These patches presumably correspond to the upstream footpoints of the arched magnetic flux tubes carrying the Evershed flow. In some cases, along a radial line extending outward from a flow channel, we find isolated patches of downflow in the C I line just outside the penumbra, with magnetic field inclination slightly beyond the horizontal (i.e., magnetic field diving beneath the surface). These patches might well correspond to the downstream footpoints of these flux tubes.

Program listing for Tuesday