83. Observing and modeling the poloidal and toroidal fields of the solar dynamo

Contributed by Robert Cameron. Posted on January 14, 2018

Cameron, R. H., Duvall , T. L, Jr., Schüssler, M., & Schunker, H.
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077, Göttingen, Germany

The solar dynamo is a cycle where in one phase motions acting on poloidal magnetic flux generates toroidal flux, and in a subsequent phase motions act on the toroidal field to reverse the poloidal field. In Ref. 1, we determined the (azimuthally averaged) toroidal magnetic field at the solar surface using SOHO/MDI and WSO data using the method described in Ref. 2. We showed that the surface toroidal field corresponded to the presence of horizontal field in the photosphere during the emergence of active regions and ephemeral regions. The surface toroidal field can therefore be considered as a good proxy for the subsurface toroidal field of the global solar dynamo. Together with the observed surface poloidal field, which corresponds to the poloidal field relevant for the solar dynamo3, we then have observations of both the poloidal and toroidal fields relevant for the global solar dynamo for four solar cycles. Figure 1 shows the observed magnetic butterfly diagrams.

Figure 1| The top panel shows the a magnetic butterfly diagram based on KPNSO/VT and SOLIS data. The bottom panel shows the surface toroidal field based on WSO data.

The basic features of the observations, over four cycles of both the poloidal and toroidal fields, can be reproduced by the updated Babcock-Leighton model1,4.


[1] R. H. Cameron, T. L. Duvall Jr., M. Schüssler, H. Schunker, 2018, A&A, 609, A56
[2] Duvall, Jr., T. L., Scherrer, P. H., Svalgaard, L., Wilcox, J. M. 1979, Sol. Phys., 61, 233
[3] R. H. Cameron, M. Schüssler, 2015, Science, 347, 1333
[4] R. H. Cameron, M. Schüssler, 2017, A&A, 559, A52

5 comments on “Observing and modeling the poloidal and toroidal fields of the solar dynamo

    1. Robert Cameron

      The two figures are compatible. In nugget 58 the color red is explicitly stated in the caption to be for negative leading polarity (i.e. positive toroidal field). This is also indicated by the arrows drawn in the figure (with an arrow to the right indicating positive toroidal field). In nugget 83, blue is used for positive toroidal field (as shown by the color bar). Hence in figure 58 red is used for positive toroidal field and in nugget 83 blue is used for positive toroidal field. Apart from this arbitrary difference in the choice of col tables, the figures are compatible.

      1. Leif Svalgaard

        No, the Title of nugget 58 states clearly that what is plotted is “WSO toroidial field” which is an observed quantity. Futhermore “red and blue being negative and positive, respectively”. The unambigous interpretation is that this refers to the observed toroidal field. That the colors also match the inferred leading polarity is irrelevant and just says something about the leading polarity, not about the observed toroidal field.

        1. Robert Cameron

          The full sentence from nugget 58 that you partially quote is:
          ‘The color coding matches the inferred leading polarity fields with red and blue being negative and positive, respectively.’ I agree the title is ‘WSO toroidal field’. Are you really claiming that the *unambiguous* interpretation interpretation is the exact opposite of what the sentence explicitly states?

          Note I am not arguing that the caption and title in nugget 58 could not have been much more clearly formulated, just that the two figures are actually consistent (given the explicit explanation of the color table in nugget 58).


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