Photospheric flux changes and the MHD approximation

It is noted that observations of changes in photospheric magnetic flux present a challenge to the conventional picture of passive emerging flux tubes. This problem is assessed through an examination of the MHD approximation; both the pressure gradient term and the thermoelectric term are considered. It is concluded that, although they may provide seed fields, the two source terms, of themselves, seem unable to explain the observed rates of flux growth. However, observations suggest that regions of rapid growth and decay of flux are connected with velocity shears; it is thus necessary to consider the possibility that these nonaxisymmetric motions may give rise to dynamo action within these local regions.