麻豆传媒

News — A researcher at Los Alamos National Laboratory has detected two world-record lightning “megaflashes.” The longest-distance flash was detected in the southern United States on April 29, 2020 and spanned more than 477 miles from Mississippi to Texas. The longest-duration lightning strike was detected over Uruguay on June 18, 2020 and lasted 17.1 seconds.

“We are now at a place where we have excellent lightning measurements, which allows us to discover surprising new aspects of its behavior,” said lead author Michael Peterson, of the Space and Remote Sensing group at Los Alamos. “Now that we have a robust record of these massive flashes, we can better understand how they occur and the impact that they have.”

These megaflashes are incredibly rare events. In order to record one from the ground, or from an aircraft or satellite in a low orbit, the sensor has to be exactly in the right place at the right time, which is very unlikely.

Now, researchers are using the National Oceanic and Atmospheric Administration’s Geostationary Lightning Mapper and other similar instruments that can map flash size from space and—more importantly— provide continuous coverage over a large portion of the Earth. No matter how rare these megaflashes are or where they occur across the instrument’s vast field of view, GLM can detect them and measure their dimensions. The Laboratory’s software, which identified the megaflashes, is also used for national security purposes.

“The increasing number of large flashes that we are seeing now compared to a few years ago, and the increasing extreme sizes and durations of these flashes are simply due to the recent monumental improvements in our ability to record these monsters,” Peterson said.

The megaflashes were verified by an evaluation committee organized by the World Meteorological Organization. The findings were published in the Bulletin of the American Meteorological Society.

The new record for the longest megaflash distance is 37 miles longer than the previous record, and the new record for duration is .37 seconds more than the previous record megaflash. The were identified by the same Los Alamos scientists in 2019.

Megaflashes do not occur in ordinary thunderstorms. They require expansive electrified clouds that discharge at sufficiently low rates in order to enable single horizontal flashes spanning extraordinary distances. These new record strikes occurred in hotspots for Mesoscale Convective System thunderstorms, the dynamics of which permit extraordinary megaflashes to occur, primarily in the Great Plains in North America and the La Plata basin in South America.

Researchers expect that these records are not the final word on lightning extremes. By continuously monitoring the satellite data, even greater lightning extremes may be identified in the future.

This research was funded by Los Alamos’ Laboratory Directed Research & Development program.
'LA-UR-22-20384'