Movie of emergence of an
active region

This movie is shows a sequence of magnetograms taken over 6 days in 1996 July when a particularly impressive active region emerged at the surface of the Sun. The data were obtained by the MDI instrument on the SOHO spacecraft, and consist of line-of-sight magnetic field measurements every 96 minutes. Upgoing magnetic fields are represented by whiter shades, downgoing fields by darker shades, with grey representing weak fields. The display chosen saturates at 500 Gauss. The images have been deprojected and solar rotation has been removed.

This region was remarkable for several things:

  • Most of the flux seems to emerge in the center of the region and then spread out, positive flux to the leading edge of the region and negative flux to the trailing edge of the region.
  • A delta spot (positive and negative fields within the same sunspot penumbra) develops and produces an X-class flare on July 9 (the first flare of this size for several years).
  • Also note how the simple dipole present for days prior to the abrupt onset of emergence is affected: the negative pore is quickly cancelled by newly-emerged positive flux, while the positive pore starts moving rapidly and becomes the leading spot of the region.

    MDI is an optical telescope operated by Stanford University. SOHO is a joint ESA/NASA satellite mission to study the Sun.