![\"Coronae](\"https:\/\/cdn.sci.news\/images\/enlarge13\/image_14586e-Coronae.jpg\")
<\/a><\/p>\nCoronae glow on the tips of spruce needles, induced by charged metal plates in a laboratory. Image credit: William Brune.<\/p>\n
For as long as thunderstorms have rolled across the planet\u2019s forests, cloud-to-ground lightning has commanded attention: splitting trunks, igniting wildfires and briefly turning night into day.<\/p>\n
But scientists are now focusing on a far subtler electrical phenomenon that forms on the tips of leaves during thunderstorms.<\/p>\n
Unlike lightning, which superheats the air to tens of thousands of degrees, coronae are weak electrical discharges, with temperatures only slightly above the surrounding air.<\/p>\n
Yet these understated sparks produce extreme amounts of hydroxyl, the atmosphere\u2019s main oxidizer, damage tree leaves, and potentially contribute charged particles to the thunderstorm cloud base.<\/p>\n
\u201cThese things actually happen; we\u2019ve seen them; we know they exist now,\u201d said Dr. Patrick McFarland, a meteorologist at the Pennsylvania State University.<\/p>\n
\u201cTo finally have concrete evidence of that\u2026is what I think is the most fun.\u201d<\/p>\n
\u201cIn the laboratory, if you turn off all the lights, close the door and block the windows, you can just barely see the coronae. They look like a blue glow,\u201d he added.<\/p>\n
For their research, Dr. McFarland and his colleagues developed a multi-component mobile instrument capable of measuring coronae on treetops and atmospheric properties that can influence their formation.<\/p>\n
The main component was a 25-cm diameter telescope that focuses the UV radiation onto a solar-blind UV camera sensitive to wavelengths between 255 and 273 nm.<\/p>\n
The scientists were able to observe coronae on sweetgum and pine trees during a thunderstorm in North Carolina.<\/p>\n
\u201cCoronae hopped among leaves and sometimes followed a branch as it swayed in the wind,\u201d they noted.<\/p>\n
The authors made similar observations on other tree species under four other thunderstorms from Florida to Pennsylvania.<\/p>\n
\u201cOur observations indicate that corona shimmer on the swath of trees beneath a thunderstorm,\u201d they said.<\/p>\n
\u201cThese coronae can alter air quality in forests, subtly damage leaves, and possibly give charge to overhead thunderstorms.\u201d<\/p>\n