Learning from Lightning

Boccippio and Goodman work at the National Space Science and Technology Center in Huntsville, Ala., as part of the Lightning Team. Cummins - from Global Atmospherics, Inc. - represents the commercial side of the investigation. The company operates the National Lightning Detection Network (NLDN), a network of about 130 time-of-arrival and magnetic direction finders covering the United States.

The Monthly Weather Review paper is based on four years of observations from OTD and NLDN. The authors feel that while significant research has been dedicated to variations in lightning flash rates, there has been a dearth of research on the relative proportions of intracloud and cloud-to-ground lightning.

NASA At least 130 time-of-arrival and magnetic direction finders, as shown in the image on the left, are positioned all over the U.S. to locate lightning strikes. Each sensor can detect the direction of a strike that's 400+ kilometers away. The strike's location is determined by triangulation.

The ratio of intracloud to cloud-to-ground lightning can help scientists detect and interpret anomalies in severe storms. Intracloud lightning is the most common and appears as channels of light emanating from a central point. Cloud-to-ground lightning is less common but more dangerous. The former type of lightning is weaker and harder to measure over long distances, while the latter is easier to measure from the ground. Global-scale measurement of both types is easier from space.

The ratio between the two types of lightning varies from storm to storm. In the past, it has been difficult to get a baseline for that ratio. As evidenced by this paper, merging satellite and ground measurements establishes an average that enables scientists to identify an anomalous ratio, or "one that is much higher than the garden variety," as Boccippio put it.