Super flashes surprise researchers

Extremely strong lightning hangs in the winter and over the sea why is puzzling

Super flashes are a thousand times stronger than normal discharges - and their temporal and spatial distribution are puzzles. © boschettophotography / iStock
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Puzzling Weather Phenomenon: Super flashes are rare, but a thousand times stronger than normal thunderstorm discharges - and surprisingly different, as revealed by the first mapping of this phenomenon. Thus, super flashes occur mainly in winter instead of summer. In addition, they occur primarily over the oceans - hotspots are located in the Mediterranean, off the European Atlantic coast and in the Andes. Why the super flashes show this pattern is still unknown.

Lightning is one of the most spectacular phenomena of our weather. With up to one billion volts, the brightly lit discharges jump between storm clouds or between clouds and the earth's surface. The air heats up to 30, 000 degrees and even gamma rays and antimatter are created. Typically, lightning strikes especially in the summer and accumulates over large, mountainous land masses - special hotspots are Africa, Asia and the American continent. In Germany, the Alpine foothills are a flash hotspot.

Thousand times stronger than normal flashes

But in addition to these classic flashes, there are real mega-discharges: With around one million joules, these super-flashes discharge the thousandfold energy of a normal flash, reaching a current of up to 100, 000 amperes. However, such super flashes are relatively rare: just about every 250, 000. Lightning belongs in this category. Exactly this has made it difficult to determine their time distribution and hotspots.

Only now is this the first time succeeded. Robert Holzworth of the University of Washington and his colleagues evaluated nine years of data from the World Wide Lightning Location Network (WWLLN). This global surveillance network consists of more than 100 stations from the Antarctic to the north of Scandinavia. Among the more than two billion detected flashes, the researchers identified around 8, 000 of the long-sought megablitz. This gave them enough data for the first time to map the distribution.

Most often in winter

The surprising result: Super flashes are distributed both spatially and temporally completely differently than the normal thunderstorm discharges. "Both the when and the where of these super flashes are very unexpected and unusual, " says Woodworth. While the normal flashes are the most common during the summer, the peak season for the super flashes between November and February is in the middle of winter, researchers said. Why they are just so common in winter, is so puzzling. display

It is also striking that the number of super flashes varies greatly from one year to the next, as reported by Holzworth and his team. Thus, these flashes reached a record level in late 2013 and 2014 was a particularly strong super flash year. "We suspect that this could be due to sunspots or cosmic rays, but that needs to be understood in the future, " says Woodworth. Even classic lightning is known to be affected by solar activity.

Screenshot of the interactive Soperblitz map clearly visible in the northeast Atlantic and Mediterranean. Holzworth et al.

Hotspots in the Mediterranean and in front of Europe's coast

Unusual is also the spatial pattern of the super flashes: "The super flashes occur predominantly over water, mostly near the coast. By contrast, 90 percent of normal lightning occurs over land, "reports Holzworth. Although it was already known that the average energy of lightning over water is greater than on land. "But that was only for the typical flashes. We did not expect such a dramatic difference, "says the researcher.

According to the new mapping, global hotspots of super flashes are the Mediterranean, the Northeast Atlantic and the Andes in South America. "In the northeastern Atlantic, the SuperBlitz card clearly shows the coast of Spain and England, " reports Holzworth. Other, weaker hotspots are located east of Japan, south of the tip of Africa and in some tropical marine areas. In the strongholds of classic flashes, however, super flashes are rather rare, as the researchers found.

Where most of the super flashes appear can be traced on an interactive map that the researchers have made available online.

How the super flashes are created and how their educational mechanisms differ from those of classic flashes is as open as the reason for their unusual distribution. "For now, we can only show that this previously unknown pattern exists, " says Holzworth. (Journal of Geophysical Research: Atmospheres, 2019; doi: 10.1029 / 2019JD030975)

Source: University of Washington

- Nadja Podbregar