FLUX EMERGENCE AND UMBRA FORMATION AFTER THE X-9 FLARE OF 1991 MARCH 22

Solar flares are generally believed to be caused by the magnetic reconnections at the sheared magnetic neutral lines. So, the study of magnetic field configuration near the flare sites would help us to understand the physics of solar flares. In a separate study, Wang & Ewell (1993) found that in NOAA region 6555, the photospheric shear in the neutral line in the delta spot was a mere 20-degrees before the flare but increased by nearly 40-degrees immediately after the X-9 flare on 1991 March 22. A new study of the evolution of spot and magnetic structure of the 1991 March 22 region reveals that a pair of new umbrae emerged suddenly on either side of the neutral line coinciding with the shear increase immediately after the flare. The umbral area increase is about 2 x 10(7) km2, with a minimum total flux of 2 x 10(20) Mx.