THE SUNSPOT AS A SELF-EXCITED DYNAMO

Observations show that there is downflow in and around sunspots. Follo wing Henoux and Somov, Heyvaerts and Hagyard, Hirayama, and Lorrain an d Koutchmy, we show that sunspots are self-excited magnetic-flux-tube dynamos run by the downflowing plasma. The azimuthal current results f rom an azimuthal upsilon x B field generated by the radial inflow of t he plasma. Comparison between various observations on sunspots with th e fields of various coils seems to indicate that the azimuthal current is distributed nearly uniformly over the umbra and penumbra, with a s light excess near the axis. The resulting ohmic power density is negli gible. The flux tube radius, at depth, is inversely proportional to th e fourth root of the ambient pressure. The Standard Solar Model of Bah call and Pinsonneau provides the pressure as a function of depth below -36 Mm.