The properties of small magnetic regions on the solar surface and the implications for the solar dynamo(s)

Details The properties of small magnetic regions on the solar surface and the implications for the solar dynamo(s) The properties of small magnetic regions on the solar surface and the implications for the solar dynamo(s)

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh52a0447h&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH52A-0447

Astronomy and Astrophysics

Astrophysics

7500 Solar Physics, Astrophysics, And Astronomy, 7524 Magnetic Fields, 7529 Photosphere, 7536 Solar Activity Cycle (2162)

Scientific paper

We study a combination of previously published work on active regions and large ephemeral regions, complemented with an analysis of the photospheric magnetic field outside active regions, as observed in SOHO/MDI full-disk magnetograms taken from the most recent sunspot minimum in 1996 to about a year after sunspot maximum in 2001. We find that bipolar active regions that emerge onto the Sun's surface are part of a smoothly decreasing frequency distribution that spans almost 4 orders of magnitude in flux and 8 orders of magnitude in frequency. Distributions of emergence latitude and dipole orientation narrow from nearly uniform for the smallest observed ephemeral regions (~ 5x 1018 Mx) up to narrowly distributed about the mean for the largest active regions (close to 1022 Mx), while the emergence frequency increases smoothly and rapidly with decreasing flux. At the low end of the flux spectrum, the cycle variation in emergence frequency is at most a factor of 1.5, in antiphase with the cycle variation of close to an order of magnitude for the large active regions. We discuss a scenario in which the ephemeral regions with fluxes below ~ 30x 1018 Mx have their origin in a turbulent dynamo, largely independent of the global sunspot cycle. We confirm that the ephemeral regions are an important source of flux for the quiet magnetic network, in particular for the smallest scales; the larger scale patterns are dominated by flux dispersing from decaying active regions. A comparison of the flux-emergence rate with the network flux implies an overall mean replacement time for flux in quiet Sun of 8-19 hrs.

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