Unusually intense continuing current in lightning produces delayed mesospheric breakdown

Ultra low frequency magnetic field measurements made 500-2000 km from posit ive lightning discharges show a signature that is consistent with unusually high amplitude cloud-to-ground continuing lightning current. The magnitude of this nearly constant current moment is as large as 60 kA km and can las t at half this amplitude for longer than 150 ms, thereby moving 640 C or mo re (assuming a 7 km vertical channel length) to the ground after the return stroke. This total charge transfer is more than an order of magnitude grea ter than most previously reported continuing currents in positive discharge s. Three cases analyzed show this strong continuing current flows before, d uring, and after sprites that initiate more than 40 ms after the return str oke. Accounting for this continuing current, quantitative analysis shows th at the total vertical lightning charge moment changes are large enough to p roduce mesospheric electrical breakdown and long-delayed sprites.