Up­side-down light­ning

Popular Science - - HEAD TRIP -

EV­ERY­ONE LOVES A LIGHT­NING SHOW: big bolts of elec­tric­ity head­ing to Earth. But there’s an en­tire dis­play above those bil­low­ing masses that you are prob­a­bly miss­ing.

In 2001, re­searchers scan­ning the sky with a low-light cam­era at Puerto Rico’s Arecibo Ob­ser­va­tory no­ticed some­thing bizarre: Light­ning ex­plod­ing from a cloud’s top and head­ing straight for space. The tra­jec­tory was baf­fling. Thun­der­bolts form when a neg­a­tive elec­tri­cal charge—gath­ered from an in­com­ing storm— builds up near the bot­tom of a cloud. If enough en­ergy ac­cu­mu­lates, it breaks free, send­ing the clas­sic bolt to Earth. More of­ten, how­ever, the elec­trons stay in the cloud, trav­el­ing up­ward un­til they hit the pos­i­tively charged top, where they can­cel out. Ex­cept in this case.

Cli­ma­tol­o­gists think un­usu­ally high wind is shov­ing all those plus signs out of the cloud, al­low­ing the flash to break free. Once loose, this back­ward light­ning—now called gi­gan­tic jets— trav­els un­til it hits the at­mos­phere’s near­est pro­ton-filled ob­ject: the iono­sphere, sit­u­ated at the edge of space about 50 miles up.

Sci­en­tists spot gi­gan­tic jets most of­ten in the trop­ics, per­haps be­cause those storms are taller with more-vi­o­lent winds. In the­ory, the jets grow slowly enough that a smart­phone cam­era can snap them. But act quickly: They last a mere sec­ond; two if you’re lucky.

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