Global Magnetic Extrapolation Based on the Synoptic Map of MDI/SOHO

We use a potential-field method to reconstruct the 3-D global coronal magnetic fields based on a Green's function solution. The related sources for the magnetic field are the observed photospheric field and the opened field at the source surface 2.6R⊙ above the photosphere. The photospheric data are the high resolution synoptic maps of the MDI/SOHO (2"/pix,1 frame/96mins).We apply this extrapolation method to analyze possible triggers for major events in large scale. As an example, the extrapolated coronal field of the active region NOAA 9077 is demonstrated.We find a good correlation between the reconstructed morphology and that of the EIT/SOHO observation.Combined with the full-disk Hα evolution we infer that a shock wave, which originated from the AR 9082 and propagated along an extrapolated loop system directly to the place of the flare,should be the direct trigger of the large event on July 14,2000.