SOHO/MDI magnetogram movie can be viewed by clicking Movie .
Figure 1 is the calculated force lines based on linear force free field model. The alpha is -0.033 Mm^-1. The upper right panel is the overall force lines and the other three are the selected force lines with different heights. The boundary magnetic field was extracted from MDI full disk magnetogram taken at 09:36:01 UT on July 14, 2000.
Potential field lines are also calculated (see figure 2 ).
The linear force-free field lines are also calculated using high resolution MDI observation, that enable us to search for the magnetic connections between the tiny magnetic patches that varies quickly and often associate with emerging, cancellation and motion, spacially relating to solar flares. The linear force-free field lines are calculated with alpha = 0.0 Mm^-1 (potential field) , alpha = -0.033 Mm^-1 . The high_res magnetogram was taken at 09:30:01 UT on July 14, 2000.
In alpha = -0.033 Mm^-1 calculated result, we can find highly sheared force lines along the neutral line ( figure 3 ) where obvious magnetic cancellation occurred. We roughly estimate the free energy stored in these magnetic systems by using E = L * I^2 /2., where L is inductance and can be calculated by L = mu0 * l / 4 / PI where l is the length of the loop that can be obtained from calculated force lines. The electric current can be obtained using mu0 * J = alpha * B. The average of the current is 0.002178 A * m^-2. If we assume that the total cross section of these loops are 400 arcsec^2, the free energy is 5.33 * 10 ^30 erg.
The magnetic flux is estimated during the period from July 10 to July 15 (see figure 4 ). The red star represents the negative flux while the green triangle is the positive flux. The black and blue lines are the best fitting of the fluxes in the first two days. The black cross is the total flux. The red, green and black lines show the percentages of the negative, positive and net fluxes. Clearly, the flux is not balanced in this active region. Unbalanced-flux active regions may relate with CMEs because (1) some magnetic flux in unbalanced-flux active regions must connect to other areas or become openned-up (large-scale magnetic field); (2) unbalanced-flux active regions are likely to generate major flares; (3) based on SOHO observation, all x-class flares are associated with CMEs.
Linear increase of the positive and negative fluxes with the same rate in the first two days reflects the balance of the newly emerged magnetic flux and the projection effect. After that the negative flux becomes constant while the positive flux keeps increasing. Both positive and negative fluxes dramatically decrease after 14 July X5.7 flare.
