Ground Truth: A Positive Cloud-to-Ground Lightning Flash

Abstract

We describe the circumstances and effects of a cloud-to-ground lightning flash that lowered positive charge and struck a residential home near Albany, New York. The characteristics of the flash were detected and recorded by a wide-band magnetic direction-finding system operating along the East Coast. The flash contained one stroke, had an estimated peak current of 70 kA and was apparently the only ground flash in the storm. A 70 mm2 hole in a section of iron roof flashing suggests that the charge transfer may have been between 25 and 150 coulomb, depending upon assumptions. Vertical shear in the horizontal wind at the time of the flash is estimated to have been 3 m s?1 km?1, a value consistent with previous observations of lightning lowering positive charge.