No abstract

Observations have been made in Ha of the vertical velocity distribution in a sunspot. Over the umbra the pattern consists of structures of scale-size 2-3". The velocity distribution undergoes oscillations with a period of about 165 s and typical amplitude • km s 1, but the pattern breaks down after one or two cycles because the period of oscillation varies typically by • 20 s from place to place. Transverse waves develop in the outer 0.1 of the umbral radius and propagate outwards with a velocity of about 20 km s -j, becoming gradually invisible by or before the outer penumbral boundary; the amplitude is about • 1 km s -1 at the umbra-penumbra border.The penumbral waves are believed to be basically of the Alfv6n type, with 0 ~ 3 • 10 -s g cm-L The umbral oscillations presumably represent gravity waves. In both cases the fluxes are inadequate by two orders of magnitude to account for the sunspot energy deficit.

Magnetograms in lines originating high in the solar atmosphere show, away from disk center, diffuse fringes of reverse polarity on the limbward side and diffuse centerwards extensions of normal polarity wherever the field is strong. Analysis of a Mg b2 magnetogram reveals that, in active regions (and, hence, wherever the magnetic network is well developed) fields cover associated supergranules completely at heights mostly below 500-600 km (zero height is at zsoo0 = 1) but possibly up to 700-800 km at great distances (e.g. >104km) from the network. These lie much lower than previously believed, mostly around the solar average temperature minimum. Near plagettes, the low-lying field has been measured out to -6000-7000 kin. One consequence is that in active regions and plagettes, the chromosphere-corona transition region probably penetrates below 600 km; another is that potential theory is inapplicable at coronal heights below about 15 000 km.A more accurate analysis requires a specific atmospheric model for magnetic regions. Attention is drawn to the need for studying the consequences for acoustic wave propagation, reflection and dissipation in regions of strong network fields.

No abstract