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Session 17 - Magnetic Fields II.
Oral session, Tuesday, July 01
Ballroom A, Chair: Paul Charbonneau

[17.02] On the Development of a Sunspot Penumbra

K. D. Leka (HAO and ASP, Nat'l Center for Atmos. Res.), A. Skumanich (HAO, Nat'l Center for Atmos. Res.)

Using data from the Advanced Stokes Polarimeter, we follow the development of a rudimentary penumbra around a small pore. A sub-hourly cadence coupled with the full vector spectro-polarimetry and non-linear least-squares inversion algorithm allows us to determine not only the vector magnetic field around the pore, but also thermodynamic parameters and Doppler shifts.

We find that a penumbra forms not by a gradual ``tilting'' of the field lines, but by the initial appearance of weaker fields at all inclinations. The distribution of these fields is sparse, but grows with time to where a fully-populated range of field strengths and inclination angles is present (as is common for fully-developed sunspots). At the same time, the range of Doppler velocities increases in the lower-field-strength areas. This implies that any difference between the start of the Evershed flow and the appearance of more inclined fields is small (less than half-hour).

We will discuss these results and their relation to the flux history of this pore, comparing it to a nearby region in which a penumbra-less pore develops from apparent quiet-sun.

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Program listing for Tuesday