LOS ANGELES (AP) — Southern California athletic director Mike Bohn has resigned. USC confirmed the 62-year-old Bohn’s resignation roughly 3 1/2 years after he succeeded Lynn Swann in the high-profile job. The Trojans’ athletic department experienced a surge of success during Bohn’s tenure. The football team made a dramatic turnaround after the hiring of coach Lincoln Riley last year, while the men’s basketball team has made three straight NCAA Tournament appearances under Andy Enfield. Bohn mentioned “ongoing health challenges” in a statement issued to the Los Angeles Times about his resignation, but provided no clear reason for the surprising move.