A measure of magnetic field discontinuity

In this paper we introduce a measure of magnetic field discontinuity, MAD, defined as Maximum Angular Difference between two adjacent magnetic field v ectors. To examine the characteristics of the MAD, we have considered sever al active region models having a quadrupolar field configuration and comput ed MADs over these active regions by approximating the 3-D magnetic fields as an ensemble of charge potential fields or linear force-free fields. The computed MAD fields are studied in comparison with other flare activity ind icators such as separators. It is found that (1) the region of high level M AD corresponds well with the separator, or practically the intersection of the separator with the plane of measurement, (2) it singles out local disco ntinuities of magnetic fields, and (3) the MAD can also be a measure of the evolutionary status of an active region. An observational test has been made for 2-D MADs, using the Yohkol SXT obse rvation of a Bare in AR 6919 and the vector magnetogram taken at the Mees S olar Observatory during this flare activity. The high level contours of 2-D MAD are found to trace well the observed soft X-ray bright points, which i ndicates that the MAD could serve as a good flare activity indicator.